,中国计量大学,浙江省生物计量及检验检疫技术重点实验室,杭州310018Progress on the mechanism of hormones regulating plant flower formation
Liping Zou, Cheng Pan, Mengxin Wang, Lin Cui, Baoyu Han,Zhejiang Provincial Key Laboratory of Biometrology and Inspection & Quarantine, China Jiliang University, Hangzhou 310018, China通讯作者: 韩宝瑜，博士，教授，研究方向：化学生态与分子生物学。E-mail:hanby15@163.com
编委: 李传友
收稿日期:2020-01-13修回日期:2020-03-11网络出版日期:2020-08-20
| 基金资助: |
Received:2020-01-13Revised:2020-03-11Online:2020-08-20
| Fund supported: |
作者简介 About authors
邹礼平,在读硕士研究生,专业方向：生物化学与分子生物学。E-mail:
摘要
开花是植物对环境的适应性表现,是在多种外源和内源信号形成的复杂成花调控网络下完成。植物激素作为最重要的内源信号参与者,在成花进程中扮演着重要角色。近年来,光周期等成花途径和表观遗传调控中激素的作用机理不断被解析。研究发现激素间存在协同和拮抗作用,并证实多种激素参与赤霉素(gibberellins, GA)途径中DELLA蛋白介导的多种成花调控途径。本文主要综述了GA在植物成花中的调控机理,同时探讨了脱落酸(abscisic acid, ABA)、生长素(auxin, IAA)、细胞分裂素(cytokinin, CTK)、水杨酸(salicylic acid, SA)、茉莉酸(jasmonic acid, JA)和乙烯(ethylene, ET)等其他内源激素在成花中的作用及其与DELLA、miRNAs和转录因子(transcription factor, TFs)等通路串联调控,为全面解析激素调控植物成花的网络提供参考。
关键词：
Abstract
Flowering is the adaptability of plants in response to the environment, which is regulated by the complex flowering control network formed by a variety of exogenous and endogenous signals. Plant hormones, the most important endogenous signal participants, play important roles in the process of plant flowering. Recent reports reveal the pivotal roles of hormones in the epigenetic regulation and flowering promotion pathway. In addition, synergistic or antagonistic interaction has been observed among many hormones. Numerous hormones have been found to be involved in the regulation of the multiple flowering development regulation and signaling pathways mediated by DELLA protein in the gibberellin (GA) pathway. In this review, we summarize the recent advances ofthe flowering mechanisms related to GA pathway and discuss the effects of abscisic acid (ABA), auxin (IAA), cytokinin (CTK), salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) on flowering, including their cross-regulation with DELLA, miRNAs, and transcription factor (TFs). This review provides a reference for further comprehensive analysis of the hormone-regulated network of plant flower formation.
Keywords：
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本文引用格式
邹礼平, 潘铖, 王梦馨, 崔林, 韩宝瑜. 激素调控植物成花机理研究进展. 遗传[J], 2020, 42(8): 739-751 doi:10.16288/j.yczz.20-014
Liping Zou.
开花是植物对环境的适应性表现,是植物从营养生长向生殖发育的转变,是决定植物繁殖成功与否的重要环节,本质是茎顶端分生组织(shoot apical meristem, SAM)由营养生长时期分化产生叶片转变为生殖发育时期形成花、果实和种子的过程[1]。植物成花过程可分为花的诱导、花芽分化和花器官的发育3个阶段,此过程与开花时间、开花数量、开花质量和花期长短密切相关,同时还对植物的观赏、食用和药用的经济价值产生直接影响[2]。成花过程是一个复杂的生理过程,该过程受外部和内部因素的共同调控,如光周期、温度以及内源激素介导的多种途径调控[2,3,4]。在过去几十年,通过对拟南芥(Arabidopsis thaliana)的成花生理和分子机制的研究,发现光周期途径、春化途径和环境温度途径主要传递光和温度等外部信号;而自主途径、赤霉素途径和年龄途径在很大程度上以内源信号为主[1,2,5~7]。可见,在自然状态下植物成花是对多种环境和内源信号识别和整合后作出的应答。
植物内源激素(plant endogenous hormones)参与植物的整个生命过程,通过在植物体内构建复杂完整的信号网络,传递外源或内源信号来调控植物的生长发育。因此,激素信号对于成花的影响非常重要[8,9]。在特定的条件下,激素信号的调控往往是将不同激素信号汇集后通过改变关键成花基因的表达水平来实现[10]。赤霉素(gibberllins, GA)作为赤霉素途径中主要的信号因子,在成花过程必然发挥着关键性的作用,但其他激素如脱落酸(abscisic acid, ABA)、生长素(auxin, IAA)、细胞分裂素(cytokinin, CTK)、水杨酸(salicylic acid, SA)、茉莉酸(jasmonic acid, JA)和乙烯(ethylene, ET)等,也是参与激素调控网络不可缺少的部分[3,11]。对于温室种植或精细化管理的作物而言,通过光周期和温度等控制外部信号可实现对成花的调控;但是对于大田种植的作物而言,则存在易被干扰、成本较高和可操作性差等缺点。因此,研究成花过程中激素的调控作用,解析植物体内信号调控网络,可为大田作物生产提供指导借鉴。本文主要对激素调控植物成花的机理研究进行了综述,并总结出部分激素互作通路模式图(图1),以期为更好地研究植物花的诱导、花芽分化和花器官发育中激素作用机理和调控机制提供参考。
图1
新窗口打开|下载原图ZIP|生成PPT图1激素在植物成花中的互作机制
成花途径关键基因用黄色高亮标记,红色和绿色分别代表激素的作用,红色代表促进、绿色代表抑制;虚线箭头代表迁移,→代表正调控,┤代表负调控,双向符号代表互相作用。GA：赤霉素;ABA：脱落酸;IAA：生长素;CTK：细胞分裂素;SA：水杨酸;JA：茉莉酸;ET：乙烯。
Fig.1The interaction mechanism of hormones in plant flower formation
CO: constans; FT: flowering locus T; AP1: apetala 1; SOC1: suppressor of overexpression of constans; LFY: leafy; SPLs: squamosa promoter binding protein-like; BOIs: botrytis susceptible1 interactors; PIFs: phytochrome interacting factor; AREB: ABA responsive element binding protein; ABI: abscisic acid-insensitive; HDA6: histone deacetylase 6; FLC: flowering locus C; SVP: short vegetative phase; MYC: myelocytomatosis proteins; JAZ: jasmonate ZIM-domain protein; MYB33: MYB domain protein 33; TFL: terminal flower。
1 赤霉素途径
GA是一类四环二萜类化合物,在植物生长发育过程中起着重要的调节作用。迄今为此,自然界中发现的GA形态结构超过136种,但是只有GA1、GA3、GA4和GA7少数形态具有生理活性[12]。近年来,随着分子遗传学和功能基因组学的不断发展,GA调控植物生长发育的模式被解析的十分透彻[13,14]。越来越多的研究表明,GA在去抑制和信号转导等方面发挥着重要的作用[14,15]。GA信号转导主要借助于GID1(GA insensitive dwarf 1)、DELLA蛋白和介导DELLA蛋白降解的其他调控因子实现,可见DELLA蛋白是GA合成及其信号转导过程中的核心因子,在GA合成以及其信号转导中发挥着重要作用。1.1 GA与植物成花
赤霉素途径调控成花是最早被发现的4条成花途径之一,拟南芥内源GA合成受阻或者破坏GA在体内的信号转导过程,成花进程均会受到影响[16]。GA信号转导是由活性GA激活的,而GA作为可移动的分子,可通过细胞膜在细胞间进行运输[17]。细胞间GA的动态平衡主要由GA合成途径中关键限速酶基因GA20ox和GA3ox、失活和降解途径中GA2ox氧化酶基因调控。GA信号转导依赖一类核蛋白DELLA的介导[18],DELLA蛋白被认为是植物生长发育和成花的抑制因子。水稻(Oryza sativa L.)中仅存在一个基因编码DELLA蛋白[19,20],而拟南芥存在5个特异性的DELLA基因,包括GAI(GA insensitive)、RGA(repressor of GAL-3)和3个gal-3-like蛋白的抑制基因(RGL1、RGL2和RGL3),这些基因既存在功能的冗余又具有特异性[8,21]。拟南芥突变体ga1-3在短日照下不开花,在长日照下呈现中度晚花现象[22]。该现象揭示赤霉素途径调控低于光周期调控,当光周期调控不起主导作用时,赤霉素途径的重要性被凸显出来。但是近期研究发现,无论光周期调控信号是否存在,GA都具有独特的调控模式促进成花。Porri等[23]发现长日照下GA也可以上调FT(flowering locus T)和TSF(twin sister of FT)蛋白的表达水平促进成花。Galv?o等[24]发现环境温度途径诱导拟南芥成花需要借助GA信号转导,DELLA在长日照下可沉默叶片中miR172和茎尖的MADS基因参与自主途径抑制成花[25],DELLA也下调年龄途径中miR156的靶基因SPLs(squamosa promoter binding protein-like)参与成花[22]。可见GA信号参与年龄、自主和环境温度等途径的调控[22,24,26~28]。FT蛋白的合成部位在叶片,但其被运送至SAM中才发挥作用[11],因此GA调控成花的作用部位分为叶片和SAM。1.2 叶片中的GA调控
众多的研究表明,当植物体内GA含量较低或者GA信号传递受阻的情况下,FT基因表达水平处于较低水平;而当叶面上外源喷洒GA或恢复GA信号传递时,FT基因表达水平上调[23,24,27~29]。这些结果支持长日照下GA可增强FT基因的转录活性这一观点。但也有研究发现叶面喷洒GA既不能改变野生型植株在短日照下FT基因的转录水平,也不能改变长日照下co突变体FT基因的转录水平[29,30]。所以,长日照下GA是否调控FT基因的表达量还需要更多的研究来验证。GA可通过多种机制调节FT基因的表达水平实现成花调控[23,24,27,28]。AP2(apetala 2)类蛋白负调节叶片中FT基因的转录活性,而叶片中DELLA可抑制miR172的表达,实现对miR172靶基因AP2的上调[31,32,33]。Yu等[27]也发现GA对miR172的调控是借助于DELLA和miR172的正调控因子SPLs来实现。当然部分SPLs(如SPL3)基因编码序列可直接与FT基因序列结合,并激活FT基因转录[34]。Yu等[27]还指出DELLA组成型激活表达后,miR172的表达量被显著下调,可能是由于DELLA与SPLs蛋白结合引起的,同时会引起FT基因转录水平下调。在突变体SUC2: ΔDELLA中过表达miR172可改善其晚花现象[31],这也证明DELLA可能是通过SPL-miR172调控模式增强对FT的转录抑制。
DELLA除了可激活FT基因的抑制因子外,还会干扰FT关键转录激活因子CO(constans)蛋白的功能。DELLA可与CO或含有CO结构域的类似物结合,使其与DNA互作而丧失功能[35,36]。因此,不论是GA含量降低还是增强DELLA蛋白水平,其最终结果都是导致FT和TSF的转录水平降低,这与CO蛋白的稳定性恰好一致[23,30]。体外研究发现,DELLA可阻止CO和NFYB(nuclear transcription factor Y subunit B)互相结合,从而使CO失去激活FT的功能[35,37]。CO与NFY(nuclear transcription factor Y)复合物的主要功能是维持染色体上FT位点的特异性结构,从而有利于FT的转录激活[38]。因此,DELLA可通过降低CO蛋白功能来阻止染色体上FT位点的特异性结构的形成[30]。但是,Hou等[28]提出DELLA与NFYB和NFYC也可以互相结合,所以DELLA的调控机制可能更为复杂。
DELLA蛋白可与多种转录因子结合同时抑制CO蛋白功能和FT基因的转录激活,其本质是通过与转录因子结合互作的方式降低与DNA的结合能力[39]。如光敏色素互作因子PIF4(phytochrome interacting factor 4)是FT的激活因子,在温敏途径中CO蛋白也可被PIF4互作激活。DELLA与PIF4结合后,PIF4的功能被抑制[40,41,42]。可见,GA利用DELLA与PIF4或PIFs类转录因子的互作机制调控植物成花时间[43]。
除了结合互作的方式外,DELLA还可通过其他机制影响转录因子[39]。Li等[44]研究发现,DELLA与转录因子PIF4的结合,不但产生“隔离”的作用,还能降解PIF4。DELLA还可以引导转录抑制因子作用于特定的基因位点,如BOIs(botrytis susceptible1 interactors)蛋白[45]。BOIs蛋白在花芽分化期富集,但需要依赖于DELLA才能被引导至FT启动子区域富集并与FT位点结合,抑制FT的转录[46]。除了依赖于DELLA的方式外,BOIs蛋白也可通过其CCT结构域与CO蛋白结合,干扰CO与DNA的识别机制[46]。同样,DELLA蛋白还可与FLC(flowering locus C)形成复合物阻碍FT基因的转录激活[47]。
1.3 SAM中的GA调控
SAM是GA调控成花的另一个作用部位。外源喷洒GA不能激活短日照下叶片内FT基因的表达,但却可以促进野生型、co突变体和ft tsf突变体成花[23,29,48,49]。非成花条件下,叶片中高含量GA诱导SAM成花,因此Hisamatsu和King[29]提出GA成花调控途径不借助于叶片中的成花基因。这可能是叶片中合成的GA被运输至SAM才激活成花基因表达,也可能是GA拥有不依赖于叶片中FT蛋白的调控机制[17]。Zhu等[50]发现叶片中合成FT蛋白在NaKR1 (sodium potassium root defective 1)蛋白作用下被运输至SAM中发挥作用。虽然GA在植物体内的精准分布情况还缺乏研究,但是GA可在细胞间被主动运输已被广泛认可[51,52]。研究发现GA4含量会在SAM花芽分化期急剧上升,与成花进程密切相关;但是通过分子水平的研究发现,该阶段SAM中与GA4生物合成相关基因并未提前呈现上调趋势,因此GA4含量的增加是由于SAM以外的部位运输补充[17]。NFL(no flowering in short day)转录因子是短日照下GA稳态的关键调控因子,nfl突变体的SAM中GA生物合成和分解代谢相关基因相对野生型分别呈现下调和上调的现象,这表明该突变体的SAM中GA呈现低活性状态;但在长日照条件下,nfl突变体与野生型类似,表现为开花表型,因此NFL及其靶基因的调控与光周期调控也密切相关[53]。SAM中GA含量变化受到多种成花基因的影响。Andrés等[54]发现长日照下SAM中GA合成关键酶基因GA20ox2(gibberellin 20-oxidase 2)表达量在花芽分化期显著增加,他们认为GA20ox2基因表达的积累与FT蛋白的激活有关,FT蛋白通过下调成花抑制因子SVP(short vegetative phase)的表达水平来增加GA20ox2的表达量。因此,在长日照下FT信号运输至SAM后,可促进GA积累,促进花芽分化。Li等[55]发现高GA含量又可反馈抑制SVP基因表达,他们认为SVP是SAM中GA生物合成相关基因的关键调控者。FLC/SVP复合物可上调GA2ox(gibberellin 2-oxidase)的表达促进GA的降解,还可促进GA合成关键酶GA3ox(gibberellin 3-oxidase)的抑制因子TEM1(tempranillo 1)和TEM2的表达[47,54]。因此,SVP/FLC复合物可以影响GA合成和代谢相关酶来调控GA在SAM中的动态平衡。除了调控GA生物合成和分解代谢的方式外,DELLA可将GA信号传递到多种调控途径。DELLA可激活miR159的转录表达,抑制MYB33(MYB domain protein 33)的活性,从而完成对花分生组织特异性基因LFY(leafy)的抑制,延缓成花进程[56,57,58,59]。也有研究指出,GA信号可直接上调LFY的激活因子SOC1(suppressor of overexpression of constans)的表达,实现对LFY的激活,该过程不依赖于DELLA和miR159/MYB33调控途径[56,60]。但是,Yu等[27]发现DELLA可抑制SPLs的转录来下调SOC1的表达水平;也有研究指出在长日照条件下,在花芽分化期SOC1可引起SAM中部分SPLs表达量的上调,从而实现自我调节的反馈回路[23,61]。可见,GA对LFY的调控存在多种复杂的调控机制。
GA也参与SAM中由miR156及其靶基因SPLs调控的年龄途径[62]。miR156-SPLs调控模式在进化上较为保守,随着植物生长发育逐渐下调miR156的水平导致SPLs的积累增加;SPLs拥有众多参与SAM成花调控的靶基因,如miR172、SOC1、AP1(apetala 1)和FUL(fruitful)等成花基因[62,63,64]。外源喷洒GA仅能轻微缓解过表达miR156植株的晚花表型[27,65],可见在SPLs积累过少时,GA对DELLA蛋白的降解并不能激活成花。所以,GA参与年龄途径的调控发生在mi156表达量降低后,参与增加SPLs的积累调控。DELLA蛋白对SPLs的调控可分为转录和转录后两个水平。DELLA蛋白抑制茎尖不同SPLs基因的转录激活[23,24]。Park等[66]和Zhang等[67]均发现DELLA与染色质重塑因子PKL(pickle)的拮抗结合可抑制SPL基因的转录。而转录后的调控是DELLA蛋白直接与SPLs结合,降低SPLs结合靶基因的活性[27,65]。越来越多的研究已经证实GA通过DELLA-SPLs互作机制调控成花,在短日照条件下这种互作机制尤为显著[27,65,68,69],但GA的具体作用与SPLs的种类密切相关。在短日照下spl15突变体与GA缺陷型突变体均呈现为极晚花表型,因此Hyun等[65]认为SPL15是DELLA在短日照下调控的关键性靶基因,只有当GA充足并消除DELLA对SPL15的抑制作用,SPL15与SOC1才能协同诱导FUL的表达,影响SAM其他成花基因的表达。但Xu等[69]的研究结果指出短日照下SPL15的成花调控作用不是唯一的,原因是SPLs序列存在高度的冗余。相反,在花分生组织中当DELLA与SPL9结合后,有助于激活AP1启动子的转录表达[70]。因此,DELLA与SPLs的互作需要根据SPL的种类及其调控的DNA序列具体分析。
2 其他激素途径
2.1 JA
JA及其衍生物属于脂质类植物激素,JA类衍生物的信号途径及应对逆境胁迫的反应机制被研究的较为透彻[71,72],但在花期调控中的作用研究较少。拟南芥中参与JA应答的HDA6(histone deacetylase 6)参与FLC染色质的去乙酰化过程,抑制FLC基因表达,这表明HDA6是JA参与成花调控的关键因子[73,74,75]。有研究显示,拟南芥JA合成缺陷型突变体表现为雄性不育,同时发现突变体的花丝延伸能力、花粉成熟和花药开裂程度均受到影响[76,77]。同时,arf6 arf8双基因突变体也呈现短花瓣、短雄蕊花丝和花药不开裂等现象[78]。而外源喷洒JA后,随着JA含量增多调节花丝成熟的ARF6(auxin response factor 6)和ARF8基因在花药开裂期大量表达,可见JA可促进雄蕊和雌蕊成熟[78]。研究表明,ARF6和ARF8分别是miR167和miR160的靶基因[78,79],因此JA与miR167和miR160共同控制ARF6和ARF8参与成花调控[80]。Zhai等[81]还发现JA可借助JAZ(jasmonate ZIM-domain protein)蛋白将信号传递给转录因子MYCs(myelocytomatosis proteins),来抑制FT的表达并延迟成花。虽然以上结果显示JA参与花器官发育或抑制FT的表达,但其在成花途径中的作用还缺乏研究,与其他激素是否存在串联调控机制也未被证实。2.2 ABA
ABA是一类倍半萜类植物激素,参与植物蛋白质和脂质合成、种子脱水耐受、种子休眠和成花等生长发育过程[82],同时ABA还参与多种非生物胁迫应答[83,84]。目前,ABA信号是否参与花芽分化仍存在争议,很多报道相互对立[85,86]。生理研究发现,ABA积累被认可有利于木本植物温州蜜柑(Satsuma Mandarin)的花芽孕育[87];但是在温州蜜柑花芽诱导期,ABA处于较低水平,在花原基形成时才上升到较高水平,故ABA对花芽分化的作用因所处阶段而异[88]。ABA在陆地棉(Gossypium hirsutum)[89]、苹果(Malus domestica)[90]的花芽分化期含量逐渐增高,可见高浓度ABA有利于花芽分化;但高含量的ABA不利于龙眼(Dimocarprs longana)的花芽形成[91]。在草本植物中,内源ABA是打破百合花(Longiflorum hybrids)鳞茎休眠促进花芽分化的关键物质[92],ABA在菊花(Chrysanthemum morifolium)花芽分化期呈现为逐渐升高的现象[93]。基因的研究发现,ABA可激活FT和TSF基因表达,有利于拟南芥的花芽分化[94,95]。在长日照下,aba1和aba2突变体呈现晚花现象,而在短日照条件下表现正常[94,95]。ABA信号可能参与激活CO转录或增强CO蛋白功能。ABA可磷酸化激活ABA反应元件结合蛋白(ABA responsive element binding protein, AREB)来促进CO的转录[96,97,98,99]。areb2 abf3 abf1突变体中CO转录处于低水平并呈现晚花表型[100,101];但在ABA缺陷型的突变体中,CO表达量虽然呈现下调趋势,却呈现极早花表型[100,102]。因此,ABA是否通过AREB调控CO转录有待进一步研究。ABA还影响CO蛋白功能和信号传递[95]。ABA可泛素化降解ABI3(abscisic acid-insensitive 3),释放与ABI3结合的CO蛋白来促进成花[35,103,104]。ABA还调控MYCs转录因子抑制FT蛋白表达,GA也存在MYC3-FT调控模式,JA调控也存在类似机制,因此ABA、GA和JA存在串联调节CO、FT蛋白功能的现象[11,81,105]。ABA还可负调控FT下游基因延迟成花。ABA可上调bZIP转录因子ABI5(abscisic acid-insensitive 5)和AP2结构域转录因子ABI4(abscisic acid-insensitive 4)的表达来激活FLC转录[106,107],降低SOC1表达量,延迟拟南芥成花。而SOC1的表达可被GA上调[56,60],可见SOC1可能是GA和ABA信号进行串联调控的关键点之一。
2.3 ET
植物催熟激素ET与果实成熟、叶片衰老、胁迫应答和成花过程都密切相关[108]。ET在植物组织内分布具有广泛性,但只有当叶片损伤、成熟或被切除才会造成ET的合成增加。有研究发现ET合成受抑制的拟南芥突变体呈现出早花表型[109],而ET组成型表达的ctr1突变体在短日照条件下呈晚花表型,可见ET可抑制拟南芥成花。Achard等[110]认为ET可促进DELLE蛋白的积累,抑制GA信号并延迟成花。低温环境下的成花延迟现象被认为属于ET调控,Alonso等[111]认为由于ET的抑制作用,虽然春化途径后拟南芥体内促进成花的miRNA被激活,但不呈现开花现象。ET可上调甘蓝型油菜(Brassica napus)中HAD19的表达表达量,在增强植物抗病性同时可促进FLC的表达来延迟成花[112]。虽然ET可调控DELLA和HAD19蛋白实现对花期的调控,但ET与其他激素在成花途径中的串联作用机制还需要深入研究。2.4 IAA
IAA是最早被鉴定的植物激素,影响植物细胞的伸长、分化,参与种子发育、侧根形成、根和叶片的生长发育等多种生理过程[19]。同时IAA也参与植物成花调控。Mai等[113]发现与IAA缺陷型突变体axr2(auxin resistant 2)在短日照下延迟成花。外源施加不同浓度IAA溶液会影响花朵的正常发育[114]。IAA是局部合成,经过极性运输至作用部位,在植物体内呈现梯度分布,这种动态分布与成花进程密切相关[115]。PIN(pin-formed)蛋白家族与IAA的极性运输密切相关[25],拟南芥pinl-1突变体缺失IAA的极性运输能力,出现针状花序,花、维管组织发育缺陷[26],外源喷洒IAA可以逆转这种情况诱导成花[116]。Przemeck等[117]发现arf5突变体仅能形成裸花序柄,因此IAA响应因子ARF5(auxin response factor 5)活性被认为与花原基的启动密切相关。与花器官发育相关基因LFY、ANT(aintegumenta)和AIL6(aintegumenta-like 6)均属于ARF5的靶基因[118]。ARFs和IAA还可以通过促进GA20ox和GA3ox的表达[119,120]、抑制DELLA蛋白表达[121]的形式参与到GA生物合成和信号传导的过程。可见,IAA可以通过调节GA含量和促进DELLA降解的方式促进成花。2.5 CTK
CTK是一类N6-取代的嘌呤衍生物,参与细胞的增殖和分化,与植物生长发育密切相关,在开花植物中CTK具有延缓衰老的作用[122]。尽管CTK是否参与成花转变目前还存在争议,但CTK调控花分生组织细胞的分裂和分化已被证实[123]。CKX(cytokinin oxidase/dehydrogenase enzymes)是催化降解CTK的关键酶,ckx3ckx5双突变体呈现异常膨大的花序和花分生长组织,因此CTK参与花芽分化中细胞分化的调控[124]。Corbesier等[125]发现成花刺激后叶片和韧皮部中内源CTK含量迅速增加;在短日照下,外源施加CTK可诱导营养生长期植物在细胞层面进行成花转变[126]。可见,CTK含量增加与成花转变的存在密切联系。此外,CTK可下调miR172的表达水平,促进AP2蛋白表达,使植物呈现花瓣增加、雄蕊和心皮增殖等缺陷型花型[31]。可见CTK与GA信号在miR172和AP2途径实现串联调控,但CTK参与成花调控的机制尚未被完全解析[127]。2.6 SA
SA可促进成花、调节种子发芽、抑制顶端优势、促进测生生长、调节膜透性等多种植物生长发育[22]。目前,有关SA调控成花的研究报道越来越多。如4 μmol/L浓度的SA可促进烟草(Nicotiana tabacum)愈伤组织形成花蕾[128]。苍耳属植物韧皮部的SA含量仅在开花期能检测到[129]。外源喷洒浓度为3~10 μmol/L的SA溶液,可刺激对光周期不敏感的柠檬属植物成花[130]。这些发现均显示出SA含量增加在诱导成花或促进花器官发育中的作用。但是外源施加SA又可缓解由营养不良胁迫引起的牵牛(Pharbitis nil)的早花现象[131],因此SA对成花的调控与植物所处状态密切相关[131,132]。外源施加SA溶液或紫外照射可诱导SA的积累,来抑制野生型拟南芥FLC转录因子的表达,从而促进成花[130]。但在SA缺陷型突变体中SA是否存在抑制FLC转录并促进成花的机制仍有争议,这是由于CO和SOC1的表达在短日照和长日照条件下是不同的。在长日照条件下,SA缺乏植物的CO和SOC1的表达水平与野生型相比下降约50%;在短日照条件下,SA缺乏植物的CO表达量与野生型相比增加2~3倍,但SOC1的表达两者间无显著差异[130]。同时,外源施加SA可逆转突变株co-1的晚花表型,但在长日照下对突变株soc1无显著改善现象[133]。可见,SA参与成花调控网络的串联点可能位于CO下游和SOC1上游区域,但具体机制以及SA是否参与成花调控还有待进行深入研究。3 结语与展望
植物成花调控不仅受外界环境因子影响,而且植物体内的各种激素存在互相协同和拮抗作用,是一个复杂的调控过程。植物激素调控是植物感受外部环境变化信号,利用多种激素的协同或拮抗的作用调整自身的生长和分化进程,增强对环境适应能力的调控方式。最新的研究表明,以DELLA介导的GA信号调节中枢及其调控的多种成花因子(如CO、FT、LFY和SOC1等),在GA和其他成花途径或激素信号途径关键调控因子的互相作用中发挥着重要作用。目前,对于激素调节植物成花的机制还未被深入解析,在不同植物的成花进程和花器官发育中激素调控机制、激素的动态变化以及在不同组织或细胞的精准分布都尚待进一步阐明。随着高通量测序技术的发展以及转录组、蛋白质组和代谢组等手段在成花调控研究中的应用,必将会全面解析激素调控植物成花的网络途径。今后对激素调控成花机理的研究可能主要集中在以下几个方面：(1)进一步阐明激素在不同环境下与各种成花途径互作的分子机制,以及多种激素在时间和空间上协同或拮抗的串联互作机制。(2)表观遗传机制及其对植物成花的生理、代谢和分子调控影响,解析激素调控成花的表观遗传规律。随着气候变化的加剧,表观遗传对成花诱导的影响越来越显著,而植物激素信号在表观遗传调控营养期到生殖期的转变过程中不可或缺。DNA甲基化、组蛋白翻译后修饰和miRNAs剪切等表观遗传调控将指导人们更好地开发适应新环境挑战的植物。(3)应用外源激素调控花芽分化或花器官发育的可行性。不同物种、品种等激素调控的差异性较大,对开花植物特别是附加值较高的花卉植物的调控可借助温室大棚调控光周期或温度等手段来实现。但是对于大田种植或附加值较低的植物,此方法成本较高。因此研究开发和应用外源激素控制成花对指导农业生产具有重要意义。
参考文献 原文顺序
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文中引用次数倒序
被引期刊影响因子
DOI:10.1016/j.cell.2006.05.005URLPMID:16713560 [本文引用: 2]
Plants rely heavily on environmental cues to control the timing of developmental transitions. We are beginning to better understand what determines the timing of two of these transitions, the switch from juvenile to adult vegetative development and the transition to flowering. In this review, we discuss how RNA silencing mechanisms may influence the juvenile-to-adult vegetative switch. We also describe the discovery and regulation of a component of
DOI:10.1111/j.1365-313X.2010.04148.xURLPMID:20409274 [本文引用: 3]
The coordination of the timing of flowering with seasonal and development cues is a critical life-history trait that has been shaped by evolution to maximize reproductive success. Decades of studying many plant species have revealed several of the fascinating systems that plants have evolved to control flowering time: such as the perception of day length in leaves, which leads to the production of a mobile signal, florigen, that promotes flowering at the shoot apical meristem; the vernalization process in which exposure to prolonged cold results in meristem competence to flower; and the juvenile to adult phase transition. Arabidopsis research has contributed greatly to understanding these systems at a molecular level.
DOI:10.1093/jxb/erv441URLPMID:26428061 [本文引用: 2]
Evolutionary success in plants is largely dependent on the successful transition from vegetative to reproductive growth. In the lifetime of a plant, flowering is not only an essential part of the reproductive process but also a critical developmental stage that can be vulnerable to environmental stresses. Exposure to stress during this period can cause substantial yield losses in seed-producing plants. However, it is becoming increasingly evident that altering flowering time is an evolutionary strategy adopted by plants to maximize the chances of reproduction under diverse stress conditions, ranging from pathogen infection to heat, salinity, and drought. Here, recent studies that have revealed new insights into how biotic and abiotic stress signals can be integrated into floral pathways are reviewed. A better understanding of how complex environmental variables affect plant phenology is important for future genetic manipulation of crops to increase productivity under the changing climate.
DOI:10.1111/mec.13683URLPMID:27144929 [本文引用: 1]
Local climatic conditions likely constitute an important selective pressure on genes underlying important fitness-related traits such as flowering time, and in many species, flowering phenology and climatic gradients strongly covary. To test whether climate shapes the genetic variation on flowering time genes and to identify candidate flowering genes involved in the adaptation to environmental heterogeneity, we used a large Medicago truncatula core collection to examine the association between nucleotide polymorphisms at 224 candidate genes and both climate variables and flowering phenotypes. Unlike genome-wide studies, candidate gene approaches are expected to enrich for the number of meaningful trait associations because they specifically target genes that are known to affect the trait of interest. We found that flowering time mediates adaptation to climatic conditions mainly by variation at genes located upstream in the flowering pathways, close to the environmental stimuli. Variables related to the annual precipitation regime reflected selective constraints on flowering time genes better than the other variables tested (temperature, altitude, latitude or longitude). By comparing phenotype and climate associations, we identified 12 flowering genes as the most promising candidates responsible for phenological adaptation to climate. Four of these genes were located in the known flowering time QTL region on chromosome 7. However, climate and flowering associations also highlighted largely distinct gene sets, suggesting different genetic architectures for adaptation to climate and flowering onset.
[本文引用: 1]
[本文引用: 1]
DOI:10.1038/nrg3291URLPMID:22898651
Plants respond to the changing seasons to initiate developmental programmes precisely at particular times of year. Flowering is the best characterized of these seasonal responses, and in temperate climates it often occurs in spring. Genetic approaches in Arabidopsis thaliana have shown how the underlying responses to changes in day length (photoperiod) or winter temperature (vernalization) are conferred and how these converge to create a robust seasonal response. Recent advances in plant genome analysis have demonstrated the diversity in these regulatory systems in many plant species, including several crops and perennials, such as poplar trees. Here, we report progress in defining the diverse genetic mechanisms that enable plants to recognize winter, spring and autumn to initiate flower development.
DOI:10.1093/jxb/erp040URLPMID:19264752 [本文引用: 1]
Gibberellins (GAs) function not only to promote the growth of plant organs, but also to induce phase transitions during development. Their involvement in flower initiation in long-day (LD) and biennial plants is well established and there is growing insight into the mechanisms by which floral induction is achieved. The extent to which GAs mediate the photoperiodic stimulus to flowering in LD plants is, with a few exceptions, less clear. Despite evidence for photoperiod-enhanced GA biosynthesis in leaves of many LD plants, through up-regulation of GA 20-oxidase gene expression, a function for GAs as transmitted signals from leaves to apices in response to LD has been demonstrated only in Lolium species. In Arabidopsis thaliana, as one of four quantitative floral pathways, GA signalling has a relatively minor influence on flowering time in LD, while in SD, in the absence of the photoperiod flowering pathway, the GA pathway assumes a major role and becomes obligatory. Gibberellins promote flowering in Arabidopsis through the activation of genes encoding the floral integrators SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), LEAFY (LFY), and FLOWERING LOCUS T (FT) in the inflorescence and floral meristems, and in leaves, respectively. Although GA signalling is not required for floral organ specification, it is essential for the normal growth and development of these organs. The sites of GA production and action within flowers, and the signalling pathways involved are beginning to be revealed.
DOI:10.1038/nature08122URLPMID:19553990 [本文引用: 2]
Plant growth and development is regulated by a structurally unrelated collection of small molecules called plant hormones. During the last 15 years the number of known plant hormones has grown from five to at least ten. Furthermore, many of the proteins involved in plant hormone signalling pathways have been identified, including receptors for many of the major hormones. Strikingly, the ubiquitin-proteasome pathway plays a central part in most hormone-signalling pathways. In addition, recent studies confirm that hormone signalling is integrated at several levels during plant growth and development.
DOI:10.1038/nrg2558URLPMID:19360022 [本文引用: 1]
Plant development is subject to hormonal growth control and adapts to environmental cues such as light or stress. Recently, significant progress has been made in elucidating hormone synthesis, signalling and degradation pathways, and in resolving spatial and temporal aspects of hormone responses. Here we review how hormones control maintenance of stem cell systems, influence developmental transitions of stem cell daughters and define developmental compartments in Arabidopsis thaliana. We also discuss how environmental cues change plant growth by modulating hormone levels and response. Future analysis of hormone crosstalk and of hormone action at both single cell and organ levels will substantially improve our understanding of how plant development adapts to changes in intrinsic and environmental conditions.
DOI:10.1016/j.ydbio.2017.03.024URLPMID:28351648 [本文引用: 1]
The transition to flowering marks a key adaptive developmental switch in plants which impacts on their survival and fitness. Different signaling pathways control the floral transition, conveying both endogenous and environmental cues. These cues are often relayed and/or modulated by different hormones, which might confer additional developmental flexibility to the floral process in the face of varying conditions. Among the different hormonal pathways, the phytohormone gibberellic acid (GA) plays a dominant role. GA is connected with the other floral pathways through the GA-regulated DELLA proteins, acting as versatile interacting modules for different signaling proteins. In this review, I will highlight the role of DELLAs as spatial and temporal modulators of different consolidated floral pathways. Next, building on recent data, I will provide an update on some emerging themes connecting other hormone signaling cascades to flowering time control. I will finally provide examples for some established as well as potential cross-regulatory mechanisms between hormonal pathways mediated by the DELLA proteins.
DOI:10.1111/jipb.12892URLPMID:31785071 [本文引用: 3]
In angiosperms, floral transition is a key developmental transition from the vegetative to reproductive growth, and requires precise regulation to maximize the reproductive success. A complex regulatory network governs this transition through integrating flowering pathways in response to multiple exogenous and endogenous cues. Phytohormones are essential for proper plant developmental regulation and have been extensively studied for their involvement in the floral transition. Among various phytohormones, gibberellin (GA) plays a major role in affecting flowering in the model plant Arabidopsis thaliana. The GA pathway interact with other flowering genetic pathways and phytohormone signaling pathways through either DELLA proteins or mediating GA homeostasis. In this review, we summarize the recent advances in understanding the mechanisms of DELLA-mediated GA pathway in flowering time control in Arabidopsis, and discuss its possible link with other phytohormone pathways during the floral transition.
[本文引用: 1]
DOI:10.1146/annurev.arplant.55.031903.141753URLPMID:15377219 [本文引用: 1]
The hormone gibberellin (GA) plays an important role in modulating diverse processes throughout plant development. In recent years, significant progress has been made in the identification of upstream GA signaling components and trans- and cis-acting factors that regulate downstream GA-responsive genes in higher plants. GA appears to derepress its signaling pathway by inducing proteolysis of GA signaling repressors (the DELLA proteins). Recent evidence indicates that the DELLA proteins are targeted for degradation by an E3 ubiquitin ligase SCF complex through the ubiquitin-26S proteasome pathway.
[本文引用: 2]
DOI:10.1016/j.cub.2011.02.036URLPMID:21549956 [本文引用: 1]
Bioactive gibberellins (GAs) are diterpene phytohormones that modulate growth and development throughout the whole life cycle of the flowering plant. Impressive advances have been made in elucidating the GA pathway with the cloning and characterization of genes encoding most GA biosynthesis and catabolism enzymes, GA receptors (GIBBERELLIN INSENSITIVE DWARF1, GID1) and early GA signaling components. Recent biochemical, genetic and structural analyses demonstrate that GA de-represses its signaling pathway by GID1-induced degradation of DELLA proteins, which are master growth repressors, via a ubiquitin-proteasome pathway. Multiple endogenous signals and environmental cues also interact with the GA-GID1-DELLA regulatory module by affecting the expression of GA metabolism genes, and hence GA content and DELLA levels. Importantly, DELLA integrates different signaling activities by direct protein-protein interaction with multiple key regulatory proteins from other pathways. Comparative studies suggest that the functional GA-GID1-DELLA module is highly conserved among vascular plants, but not in the bryophytes. Interestingly, differentiation of the moss Physcomitrella patens is regulated by as yet unidentified ent-kaurene-derived diterpenes, which are distinct from the common active GAs in vascular plants.
DOI:10.1104/pp.100.1.403URLPMID:16652976 [本文引用: 1]
Mutants of Arabidopsis thaliana deficient in gibberellin synthesis (ga1-3 and ga1-6), and a gibberellin-insensitive mutant (gai) were compared to the wild-type (WT) Landsberg erecta line for flowering time and leaf number when grown in either short days (SD) or continuous light (CL). The ga1-3 mutant, which is severely defective in ent-kaurene synthesis because it lacks most of the GA1 gene, never flowered in SD unless treated with exogenous gibberellin. After a prolonged period of vegetative growth, this mutant eventually underwent senescence without having produced flower buds. The gai mutant and the
DOI:10.1105/tpc.106.042317URLPMID:16920780 [本文引用: 3]
Flower initiation in Arabidopsis thaliana under noninductive short-day conditions is dependent on the biosynthesis of the plant hormone gibberellin (GA). This dependency can be explained, at least partly, by GA regulation of the flower meristem identity gene LEAFY (LFY) and the flowering time gene SUPPRESSOR OF CONSTANS1. Although it is well established that GA(4) is the active GA in the regulation of Arabidopsis shoot elongation, the identity of the GA responsible for the regulation of Arabidopsis flowering has not been established. Through a combination of GA quantifications and sensitivity assays, we show that GA(4) is the active GA in the regulation of LFY transcription and Arabidopsis flowering time under short-day conditions. The levels of GA(4) and sucrose increase dramatically in the shoot apex shortly before floral initiation, and the regulation of genes involved in GA metabolism suggests that this increase is possibly due to transport of GAs and sucrose from outside sources to the shoot apex. Our results demonstrate that in the dicot Arabidopsis, in contrast with the monocot Lolium temulentum, GA(4) is the active GA in the regulation of both shoot elongation and flower initiation.
DOI:10.1126/science.1083217URLPMID:12649470 [本文引用: 1]
DOI:10.1016/j.tplants.2015.10.019URLPMID:26651917 [本文引用: 2]
Auxin coordinates plant development largely via hierarchical control of gene expression. During the past decades, the study of early auxin genes paired with the power of Arabidopsis genetics have unraveled key nuclear components and molecular interactions that perceive the hormone and activate primary response genes. Recent research in the realm of structural biology allowed unprecedented insight into: (i) the recognition of auxin-responsive DNA elements by auxin transcription factors; (ii) the inactivation of those auxin response factors by early auxin-inducible repressors; and (iii) the activation of target genes by auxin-triggered repressor degradation. The biophysical studies reviewed here provide an impetus for elucidating the molecular determinants of the intricate interactions between core components of the nuclear auxin response module.
DOI:10.1046/j.1365-313x.2001.01173.xURLPMID:11737783 [本文引用: 1]
The distribution and biosynthesis of indole-3-acetic acid (IAA) was investigated during early plant development in Arabidopsis. The youngest leaves analysed, less than 0.5 mm in length, contained 250 pg mg(-1) of IAA and also exhibited the highest relative capacity to synthesize this hormone. A decrease of nearly one hundred-fold in IAA content occurred as the young leaves expanded to their full size, and this was accompanied by a clear shift in both pool size and IAA synthesis capacity. The correlation between high IAA content and intense cell division was further verified in tobacco leaves, where a detailed analysis revealed that dividing mesophyll tissue contained ten-fold higher IAA levels than tissue growing solely by elongation. We demonstrated that all parts of the young Arabidopsis plant can potentially contribute to the auxin needed for growth and development, as not only young leaves, but also all other parts of the plant such as cotyledons, expanding leaves and root tissues have the capacity to synthesize IAA de novo. We also observed that naphthylphthalamic acid (NPA) treatment induced tissue-dependent feedback inhibition of IAA biosynthesis in expanding leaves and cotyledons, but intriguingly not in young leaves or in the root system. This observation supports the hypothesis that there is a sophisticated tissue-specific regulatory mechanism for auxin biosynthesis. Finally, a strict requirement for maintaining the pool sizes of IAA was revealed as reductions in leaf expansion followed both decreases and increases in the IAA levels in developing leaves. This indicates that leaves are not only important sources for IAA synthesis, but that normal leaf expansion depends on rigorous control of IAA homeostasis.
DOI:10.1073/pnas.1304250110URLPMID:23878229 [本文引用: 1]
Plant growth is regulated by a complex network of signaling events. Points of convergence for the signaling cross-talk between the phytohormones auxin and gibberellin (GA), which partly control overlapping processes during plant development, are largely unknown. At the cellular level, auxin responses are controlled by members of the AUXIN RESPONSE FACTOR (ARF) family of transcription factors as well as AUXIN/INDOLE-3-ACETIC ACID INDUCIBLE (AUX/IAA) proteins that repress the activity of at least a subset of ARFs. Here, we show that the two paralogous GATA transcription factors GATA, NITRATE-INDUCIBLE, CARBON-METABOLISM INVOLVED (GNC) and GNC-LIKE (GNL)/CYTOKININ-RESPONSIVE GATA FACTOR1 (CGA1) are direct and critical transcription targets downstream from ARF2 in the control of greening, flowering time, and senescence. Mutants deficient in the synthesis or signaling of the phytohormone GA are also impaired in greening, flowering, and senescence, and interestingly, GNC and GNL were previously identified as important transcription targets of the GA signaling pathway. In line with a critical regulatory role for GNC and GNL downstream from both auxin and GA signaling, we show here that the constitutive activation of GA signaling is sufficient to suppress arf2 mutant phenotypes through repression of GNC and GNL. In addition, we show that GA promotes ARF2 protein abundance through a translation-dependent mechanism that could serve to override the autoinhibitory negative feedback regulation of ARF2 on its own transcription and thereby further promote GA signaling.
DOI:10.1016/j.jplph.2017.03.018URLPMID:28419906 [本文引用: 4]
Reproduction is one of the most important phases in an organism's lifecycle. In the case of angiosperm plants, flowering provides the major developmental transition from the vegetative to the reproductive stage, and requires genetic and epigenetic reprogramming to ensure the success of seed production. Flowering is regulated by a complex network of genes that integrate multiple environmental cues and endogenous signals so that flowering occurs at the right time; hormone regulation, signaling and homeostasis are very important in this process. Working alone or in combination, hormones are able to promote flowering by epigenetic regulation. Some plant hormones, such as gibberellins, jasmonic acid, abscisic acid and auxins, have important effects on chromatin compaction mediated by DNA methylation and histone posttranslational modifications, which hints at the role that epigenetic regulation may play in flowering through hormone action. miRNAs have been viewed as acting independently from DNA methylation and histone modification, ignoring their potential to interact with hormone signaling - including the signaling of auxins, gibberellins, ethylene, jasmonic acid, salicylic acid and others - to regulate flowering. Therefore, in this review we examine new findings about interactions between epigenetic mechanisms and key players in hormone signaling to coordinate flowering.
DOI:10.1242/dev.077164URL [本文引用: 7]
DOI:10.1242/dev.080879URLPMID:22992955 [本文引用: 5]
The transition from vegetative to reproductive development is a central event in the plant life cycle. To time the induction of flowering correctly, plants integrate environmental and endogenous signals such as photoperiod, temperature and hormonal status. The hormone gibberellic acid (GA) has long been known to regulate flowering. However, the spatial contribution of GA signaling in flowering time control is poorly understood. Here we have analyzed the effect of tissue-specific misexpression of wild-type and GA-insensitive (dellaDelta17) DELLA proteins on the floral transition in Arabidopsis thaliana. We demonstrate that under long days, GA affects the floral transition by promoting the expression of flowering time integrator genes such as FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF) in leaves independently of CONSTANS (CO) and GIGANTEA (GI). In addition, GA signaling promotes flowering independently of photoperiod through the regulation of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes in both the leaves and at the shoot meristem. Our data suggest that GA regulates flowering by controlling the spatial expression of floral regulatory genes throughout the plant in a day-length-specific manner.
DOI:10.1007/s00018-006-6116-5URLPMID:17013565 [本文引用: 2]
The plant hormone auxin plays crucial roles in regulating plant growth development, including embryo and root patterning, organ formation, vascular tissue differentiation and growth responses to environmental stimuli. Asymmetric auxin distribution patterns have been observed within tissues, and these so-called auxin gradients change dynamically during different developmental processes. Most auxin is synthesized in the shoot and distributed directionally throughout the plant. This polar auxin transport is mediated by auxin influx and efflux facilitators, whose subcellular polar localizations guide the direction of auxin flow. The polar localization of PIN auxin efflux carriers changes in response to developmental and external cues in order to channel auxin flow in a regulated manner for organized growth. Auxin itself modulates the expression and subcellular localization of PIN proteins, contributing to a complex pattern of feedback regulation. Here we review the available information mainly from studies of a model plant, Arabidopsis thaliana, on the generation of auxin gradients, the regulation of polar auxin transport and further downstream cellular events.
DOI:10.1105/tpc.3.7.677URLPMID:12324609 [本文引用: 2]
The pin-formed mutant pin 1-1, one of the Arabidopsis flower mutants, has several structural abnormalities in inflorescence axes, flowers, and leaves. In some cases, pin1-1 forms a flower with abnormal structure (wide petals, no stamens, pistil-like structure with no ovules in the ovary) at the top of inflorescence axes. In other cases, no floral buds are formed on the axes. An independently isolated allelic mutant (pin1-2) shows similar phenotypes. These mutant phenotypes are exactly the same in wild-type plants cultured in the presence of chemical compounds known as auxin polar transport inhibitors: 9-hydroxyfluorene-9-carboxylic acid or N-(1-naphthyl)phthalamic acid. We tested the polar transport activity of indole-3-acetic acid and the endogenous amount of free indole-3-acetic acid in the tissue of inflorescence axes of the pin1 mutants and wild type. The polar transport activity in the pin 1-1 mutant and in the pin1-2 mutant was decreased to 14% and 7% of wild type, respectively. These observations strongly suggest that the normal level of polar transport activity in the inflorescence axes is required in early developmental stages of floral bud formation in Arabidopsis and that the primary function of the pin1 gene is auxin polar transport in the inflorescence axis.
DOI:10.1104/pp.111.174417URLPMID:21398257 [本文引用: 8]
Histone acetylation and deacetylation play an important role in epigenetic controls of gene expression. HISTONE DEACETYLASE6 (HDA6) is a REDUCED POTASSIUM DEPENDENCY3-type histone deacetylase, and the Arabidopsis (Arabidopsis thaliana) hda6 mutant axe1-5 displayed a late-flowering phenotype. axe1-5/flc-3 double mutants flowered earlier than axe1-5 plants, indicating that the late-flowering phenotype of axe1-5 was FLOWERING LOCUS C (FLC) dependent. Bimolecular fluorescence complementation, in vitro pull-down, and coimmunoprecipitation assays revealed the protein-protein interaction between HDA6 and the histone demethylase FLD. It was found that the SWIRM domain in the amino-terminal region of FLD and the carboxyl-terminal region of HDA6 are responsible for the interaction between these two proteins. Increased levels of histone H3 acetylation and H3K4 trimethylation at FLC, MAF4, and MAF5 were found in both axe1-5 and fld-6 plants, suggesting functional interplay between histone deacetylase and demethylase in flowering control. These results support a scenario in which histone deacetylation and demethylation cross talk are mediated by physical association between HDA6 and FLD. Chromatin immunoprecipitation analysis indicated that HDA6 bound to the chromatin of several potential target genes, including FLC and MAF4. Genome-wide gene expression analysis revealed that, in addition to genes related to flowering, genes involved in gene silencing and stress response were also affected in hda6 mutants, revealing multiple functions of HDA6. Furthermore, a subset of transposons was up-regulated and displayed increased histone hyperacetylation, suggesting that HDA6 can also regulate transposons through deacetylating histone.
DOI:10.1038/ncomms5601URLPMID:25105952 [本文引用: 3]
Nuclear factor Y (NF-Y) is a conserved heterotrimeric transcription factor complex that binds to the CCAAT motifs within the promoter region of many genes. In plants, a large number of genes code for variants of each NF-YA, B or C subunit that can assemble in a combinatorial fashion. Here, we report the discovery of an Arabidopsis NF-Y complex that exerts epigenetic control over flowering time by integrating environmental and developmental signals. We show that NF-Y interacts with CONSTANS in the photoperiod pathway and DELLAs in the gibberellin pathway, to directly regulate the transcription of SOC1, a major floral pathway integrator. This NF-Y complex binds to a unique cis-element within the SOC1 promoter to modulate trimethylated H3K27 levels, partly through a H3K27 demethylase REF6. Our findings establish NF-Y complexes as critical mediators of epigenetic marks that regulate the response to environmental or intrinsic signals in plants.
DOI:10.1093/jxb/ern232URLPMID:18931352 [本文引用: 4]
Signals produced in leaves are transported to the shoot apex where they cause flowering. Protein of the gene FLOWERING LOCUS T (FT) is probably a long day (LD) signal in Arabidopsis. In the companion paper, rapid LD increases in FT expression associated with flowering driven photosynthetically in red light were documented. In a far red (FR)-rich LD, along with FT there was a potential role for gibberellin (GA). Here, with the GA biosynthesis dwarf mutant ga1-3, GA(4)-treated plants flowered after 26 d in short days (SD) but untreated plants were still vegetative after 6 months. Not only was FT expression low in SD but applied GA bypassed some of the block to flowering in ft-1. On transfer to LD, ga1-3 only flowered when treated simultaneously with GA, and FT expression increased rapidly (<19.5 h) and dramatically (15-fold). In contrast, in the wild type in LD there was little requirement for GA for FT increase and flowering so its endogenous GA content was near to saturating. Despite this permissive role for endogenous GA in Columbia, RNA interference (RNAi) silencing of the GA biosynthesis gene, GA 20-OXIDASE2, revealed an additional, direct role for GA in LD. Flowering took twice as long after silencing the LD-regulated gene, GA 20-OXIDASE2. Such independent LD input by FT and GA reflects their non-sympatric expression (FT in the leaf blade and GA 20-OXIDASE2 in the petiole). Overall, FT acts as the main LD floral signal in Columbia and GA acts on flowering both via and independently of FT.
DOI:10.1104/pp.16.00891URLPMID:27406167 [本文引用: 3]
Gibberellin (GA) and photoperiod pathways have recently been demonstrated to collaboratively modulate flowering under long days (LDs). However, the molecular mechanisms underlying this collaboration remain largely unclear. In this study, we found that GA-induced expression of FLOWERING LOCUS T (FT) under LDs was dependent on CONSTANS (CO), a critical transcription factor positively involved in photoperiod signaling. Mechanistic investigation revealed that DELLA proteins, a group of crucial repressors in GA signaling, physically interacted with CO. The DELLA-CO interactions repressed the transcriptional function of CO protein. Genetic analysis demonstrated that CO acts downstream of DELLA proteins to regulate flowering. Disruption of CO rescued the earlier flowering phenotype of the gai-t6 rga-t2 rgl1-1 rgl2-1 mutant (dellap), while a gain-of-function mutation in GA INSENSITIVE (GAI, a member of the DELLA gene) repressed the earlier flowering phenotype of CO-overexpressing plants. In addition, the accumulation of DELLA proteins and mRNAs was rhythmic, and REPRESSOR OF GA1-3 protein was noticeably decreased in the long-day afternoon, a time when CO protein is abundant. Collectively, these results demonstrate that the DELLA-CO cascade inhibits CO/FT-mediated flowering under LDs, which thus provide evidence to directly integrate GA and photoperiod signaling to synergistically modulate flowering under LDs.
DOI:10.1105/tpc.016238URLPMID:14555699 [本文引用: 3]
MicroRNAs (miRNAs) are approximately 21-nucleotide noncoding RNAs that have been identified in both animals and plants. Although in animals there is direct evidence implicating particular miRNAs in the control of developmental timing, to date it is not known whether plant miRNAs also play a role in regulating temporal transitions. Through an activation-tagging approach, we demonstrate that miRNA 172 (miR172) causes early flowering and disrupts the specification of floral organ identity when overexpressed in Arabidopsis. miR172 normally is expressed in a temporal manner, consistent with its proposed role in flowering time control. The regulatory target of miR172 is a subfamily of APETALA2 (AP2) transcription factor genes. We present evidence that miR172 downregulates these target genes by a translational mechanism rather than by RNA cleavage. Gain-of-function and loss-of-function analyses indicate that two of the AP2-like target genes normally act as floral repressors, supporting the notion that miR172 regulates flowering time by downregulating AP2-like target genes.
DOI:10.1126/science.1088060URLPMID:12893888 [本文引用: 1]
Plant microRNAs (miRNAs) show a high degree of sequence complementarity to, and are believed to guide the cleavage of, their target messenger RNAs. Here, I show that miRNA172, which can base-pair with the messenger RNA of a floral homeotic gene, APETALA2, regulates APETALA2 expression primarily through translational inhibition. Elevated miRNA172 accumulation results in floral organ identity defects similar to those in loss-of-function apetala2 mutants. Elevated levels of mutant APETALA2 RNA with disrupted miRNA172 base pairing, but not wild-type APETALA2 RNA, result in elevated levels of APETALA2 protein and severe floral patterning defects. Therefore, miRNA172 likely acts in cell-fate specification as a translational repressor of APETALA2 in Arabidopsis flower development.
DOI:10.1016/j.cub.2007.05.009URLPMID:17540570 [本文引用: 1]
Several endogenous and environmental factors need to be integrated to time the onset of flowering. Genetic and molecular analyses, primarily in Arabidopsis thaliana and rice, have shown that CONSTANS (CO) and FLOWERING LOCUS T (FT) play central roles in photoperiod-dependent flowering. The overall picture is that CO acts in the phloem companion cells of leaves and that its main effect is to induce FT mRNA in these cells. Surprisingly, FT, a small globular protein of 20 kDa, interacts at the shoot apex with the bZIP transcription factor FLOWERING LOCUS D (FD) to induce downstream targets. Given that green fluorescent protein (GFP), which as a monomer is 27 kDa, can be easily exported to sink tissue including flowers when expressed in phloem companion cells, the latter finding strongly implied that FT protein is the mobile floral-inductive signal. In agreement with this hypothesis, an FT-GFP fusion, just like GFP, can be exported from the phloem of both rice and Arabidopsis. It has been unknown, however, whether mobile FT protein is sufficient for transmitting the flowering signal. Here we show that FT mRNA is required in phloem companion cells where it acts partially redundant with its paralog TWIN SISTER OF FT (TSF) to induce flowering. Furthermore, we have devised a method that uncouples FT mRNA and protein effects in vivo. We demonstrate that export of FT protein from phloem companion cells is sufficient to induce flowering.
DOI:10.1104/pp.111.192369URLPMID:22427344 [本文引用: 1]
The flowering time of plants is affected by modest changes in ambient temperature. However, little is known about the regulation of ambient temperature-responsive flowering by small RNAs. In this study, we show that the microRNA156 (miR156)-SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3 (SPL3) module directly regulates FLOWERING LOCUS T (FT) expression in the leaf to control ambient temperature-responsive flowering. Overexpression of miR156 led to more delayed flowering at a lower ambient temperature (16 degrees C), which was associated with down-regulation of FT and FRUITFULL expression. Among miR156 target genes, SPL3 mRNA levels were mainly reduced, probably because miR156-mediated cleavage of SPL3 mRNA was higher at 16 degrees C. Overexpression of miR156-resistant SPL3 [SPL3(-)] caused early flowering, regardless of the ambient temperature, which was associated with up-regulation of FT and FRUITFULL expression. Reduction of miR156 activity by target mimicry led to a phenotype similar to that of SUC2::rSPL3 plants. FT up-regulation was observed after dexamethasone treatment in GVG-rSPL3 plants. Misexpression and artificial microRNA-mediated suppression of FT in the leaf dramatically altered the ambient temperature-responsive flowering of plants overexpressing miR156 and SPL3(-). Chromatin immunoprecipitation assay showed that the SPL3 protein directly binds to GTAC motifs within the FT promoter. Lesions in TERMINAL FLOWER1, SHORT VEGETATIVE PHASE, and EARLY FLOWERING3 did not alter the expression of miR156 and SPL3. Taken together, our data suggest that the interaction between the miR156-SPL3 module and FT is part of the regulatory mechanism controlling flowering time in response to ambient temperature.
DOI:10.1111/j.1469-8137.2010.03251.xURLPMID:20406410 [本文引用: 3]
CONSTANS is an evolutionarily-conserved central component of the genetic pathway that controls the onset of flowering in response to daylength. However, the specific biochemical mechanism by which the CONSTANS protein regulates the expression of its target genes remains largely unknown. *By using a combination of cell-based expression analysis and in vitro DNA binding studies, we have demonstrated that CONSTANS possesses transcriptional activation potential and is capable of directly binding to DNA. *CONSTANS was found to bind DNA via a unique sequence element containing a consensus TGTG(N2-3)ATG motif. This element is present in tandem within the FLOWERING LOCUS T promoter and is sufficient for CO binding and activity. The conserved CCT (CONSTANS, CONSTANS-like and TOC1) domain of CONSTANS was shown to be required for its recruitment to the DNA motif and other CCT-containing proteins were also found to have the ability to regulate gene expression via this element. *The CCAAT box, which has been previously hypothesized as a recruitment site for complexes containing the CONSTANS protein, potentiated CONSTANS-mediated activation but was not essential for CONSTANS recruitment to a target promoter or for its activity as a transcriptional factor.
DOI:10.1002/1873-3468.12076URLPMID:26801684 [本文引用: 1]
Proper timing of flowering is essential for reproduction of plants. Although it is well known that both light and gibberellin (GA) signaling play critical roles in promoting flowering in Arabidopsis thaliana, whether and how they are integrated to regulate flowering remain largely unknown. Here, we show through biochemical studies that DELLA proteins physically interact with CONSTANS (CO). Furthermore, the interaction of CO with NF-YB2 is inhibited by the DELLA protein, RGA. Our findings suggest that regulation of flowering by GA signaling in leaves under long days is mediated, at least in part, through repression of DELLA proteins on CO, providing a molecular link between DELLA proteins, key components in GA signaling pathway, and CO, a critical flowering activator in photoperiod signaling pathway.
DOI:10.1007/s00425-008-0773-6URLPMID:18600346 [本文引用: 1]
Accumulating evidence supports a role for members of the plant Nuclear Factor Y (NF-Y) family of CCAAT-box binding transcription factors in the regulation of flowering time. In this study we have used a genetic approach to show that the homologous proteins NF-YB3 and NF-YB2 have comparable activities and play additive roles in the promotion of flowering, specifically under inductive photoperiodic conditions. We demonstrate that NF-YB2 and NF-YB3 are both essential for the normal induction of flowering by long-days and act through regulation of the expression of FLOWERING LOCUS T (FT). Using an ELISA-based in-vitro assay, we provide a novel demonstration that plant NF-YB subunits are capable of directly binding to a CCAAT-box containing region of the FLOWERING LOCUS T promoter as part of an NF-Y trimer in combination with the yeast HAP2 and HAP5 subunits. These results support an emerging model in which NF-Y complexes provide a component of the DNA target specificity for transcriptional regulators such as CONSTANS.
DOI:10.1105/tpc.113.120352URLPMID:24610724 [本文引用: 1]
For many plant species, reproductive success relies on the proper timing of flowering, and photoperiod provides a key environmental input. Photoperiod-dependent flowering depends on timely expression of FLOWERING LOCUS T (FT); however, the coordination of various cis-regulatory elements in the FT promoter is not well understood. Here, we provide evidence that long-distance chromatin loops bring distal enhancer elements into close association with the proximal promoter elements bound by CONSTANS (CO). Additionally, we show that NUCLEAR FACTOR Y (NF-Y) binds a CCAAT box in the distal enhancer element and that CCAAT disruption dramatically reduces FT promoter activity. Thus, we propose the recruitment model of photoperiod-dependent flowering where NF-Y complexes, bound at the FT distal enhancer element, help recruit CO to proximal cis-regulatory elements and initiate the transition to reproductive growth.
DOI:10.1016/j.molp.2015.09.011URLPMID:26415696 [本文引用: 2]
Plant phenotypic plasticity is controlled by diverse hormone pathways, which integrate and convey information from multiple developmental and environmental signals. Moreover, in plants many processes such as growth, development, and defense are regulated in similar ways by multiple hormones. Among them, gibberellins (GAs) are phytohormones with pleiotropic actions, regulating various growth processes throughout the plant life cycle. Previous work has revealed extensive interplay between GAs and other hormones, but the molecular mechanism became apparent only recently. Molecular and physiological studies have demonstrated that DELLA proteins, considered as master negative regulators of GA signaling, integrate multiple hormone signaling pathways through physical interactions with transcription factors or regulatory proteins from different families. In this review, we summarize the latest progress in GA signaling and its direct crosstalk with the main phytohormone signaling, emphasizing the multifaceted role of DELLA proteins with key components of major hormone signaling pathways.
DOI:10.1111/tpj.13183URLPMID:27117775 [本文引用: 1]
Plants detect changes in day length to induce seasonal patterns of flowering. The photoperiodic pathway accelerates the flowering of Arabidopsis thaliana under long days (LDs) whereas it is inactive under short days (SDs), resulting in delayed flowering. This delay is overcome by exposure of plants to high temperature (27 degrees C) under SDs (27 degrees C-SD). Previously, the high-temperature flowering response was proposed to involve either the impaired activity of MADS-box transcription factor (TF) floral repressors or PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) TF-mediated activation of FLOWERING LOCUS T (FT), which encodes the output signal of the photoperiodic pathway. We integrate these observations by studying several PIFs, the MADS-box SHORT VEGETATIVE PHASE (SVP) and the photoperiodic pathway under 27 degrees C-SD. We find that the mRNAs of FT and its paralogue TWIN SISTER OF FT (TSF) are increased at dusk under 27 degrees C-SD compared with 21 degrees C-SD, and that this requires PIF4 and PIF5 as well as CONSTANS (CO), a TF that promotes flowering under LDs. The CO and PIF4 proteins are present at dusk under 27 degrees C-SD, and they physically interact. Although Col-0 plants flower at similar times under 27 degrees C-SD and 21 degrees C-LD the expression level of FT is approximately 10-fold higher under 21 degrees C-LD, suggesting that responsiveness to FT is also increased under 27 degrees C-SD, perhaps as a result of the reduced activity of SVP in the meristem. Accordingly, only svp-41 ft-10 tsf-1 plants flowered at the same time under 21 degrees C-SD and 27 degrees C-SD. Thus, we propose that under non-inductive SDs, elevated temperatures increase the activity and sensitize the response to the photoperiod pathway.
DOI:10.1038/nature10928URL [本文引用: 1]
DOI:10.1038/nature06448URLPMID:18216856 [本文引用: 1]
Light and gibberellins (GAs) mediate many essential and partially overlapping plant developmental processes. DELLA proteins are GA-signalling repressors that block GA-induced development. GA induces degradation of DELLA proteins via the ubiquitin/proteasome pathway, but light promotes accumulation of DELLA proteins by reducing GA levels. It was proposed that DELLA proteins restrain plant growth largely through their effect on gene expression. However, the precise mechanism of their function in coordinating GA signalling and gene expression remains unknown. Here we characterize a nuclear protein interaction cascade mediating transduction of GA signals to the activity regulation of a light-responsive transcription factor. In the absence of GA, nuclear-localized DELLA proteins accumulate to higher levels, interact with phytochrome-interacting factor 3 (PIF3, a bHLH-type transcription factor) and prevent PIF3 from binding to its target gene promoters and regulating gene expression, and therefore abrogate PIF3-mediated light control of hypocotyl elongation. In the presence of GA, GID1 proteins (GA receptors) elevate their direct interaction with DELLA proteins in the nucleus, trigger DELLA protein's ubiquitination and proteasome-mediated degradation, and thus release PIF3 from the negative effect of DELLA proteins.
DOI:10.1111/tpj.13051URLPMID:26466761 [本文引用: 1]
Distinct molecular mechanisms integrate changes in ambient temperature into the genetic pathways that govern flowering time in Arabidopsis thaliana. Temperature-dependent eviction of the histone variant H2A.Z from nucleosomes has been suggested to facilitate the expression of FT by PIF4 at elevated ambient temperatures. Here we show that, in addition to PIF4, PIF3 and PIF5, but not PIF1 and PIF6, can promote flowering when expressed specifically in phloem companion cells (PCC), where they can induce FT and its close paralog, TSF. However, despite their strong potential to promote flowering, genetic analyses suggest that the PIF genes seem to have only a minor role in adjusting flowering in response to photoperiod or high ambient temperature. In addition, loss of PIF function only partially suppressed the early flowering phenotype and FT expression of the arp6 mutant, which is defective in H2A.Z deposition. In contrast, the chemical inhibition of gibberellic acid (GA) biosynthesis resulted in a strong attenuation of early flowering and FT expression in arp6. Furthermore, GA was able to induce flowering at low temperature (15 degrees C) independently of FT, TSF, and the PIF genes, probably directly at the shoot apical meristem. Together, our results suggest that the timing of the floral transition in response to ambient temperature is more complex than previously thought and that GA signaling might play a crucial role in this process.
DOI:10.1038/ncomms11868URLPMID:27282989 [本文引用: 1]
Light and gibberellins (GAs) antagonistically regulate hypocotyl elongation in plants. It has been demonstrated that DELLAs, which are negative regulators of GA signalling, inhibit phytochrome-interacting factors 3 and 4 (PIF3 and PIF4) by sequestering their DNA-recognition domains. However, it is unclear whether there are other mechanisms of regulatory crosstalk between DELLAs and PIFs. Here, we demonstrate that DELLAs negatively regulate the abundance of four PIF proteins through the ubiquitin-proteasome system. Reduction of PIF3 protein abundance by DELLAs correlates closely with reduced hypocotyl elongation. Both sequestration and degradation of PIF3 by DELLAs contribute to a reduction in PIF3 binding to its target genes. Thus, we show that promotion of PIF degradation by DELLAs is required to coordinate light and GA signals, and the dual regulation of transcription factors by DELLAs by both sequestration and degradation may be a general mechanism.
DOI:10.1105/tpc.112.108951URLPMID:23482857 [本文引用: 1]
DELLA proteins, consisting of GA INSENSITIVE, REPRESSOR OF GA1-3, RGA-LIKE1 (RGL1), RGL2, and RGL3, are central repressors of gibberellin (GA) responses, but their molecular functions are not fully understood. We isolated four DELLA-interacting RING domain proteins, previously designated as BOTRYTIS SUSCEPTIBLE1 INTERACTOR (BOI), BOI-RELATED GENE1 (BRG1), BRG2, and BRG3 (collectively referred to as BOIs). Single mutants of each BOI gene failed to significantly alter GA responses, but the boi quadruple mutant (boiQ) showed a higher seed germination frequency in the presence of paclobutrazol, precocious juvenile-to-adult phase transition, and early flowering, all of which are consistent with enhanced GA signaling. By contrast, BOI overexpression lines displayed phenotypes consistent with reduced GA signaling. Analysis of a gai-1 boiQ pentuple mutant further indicated that the GAI protein requires BOIs to inhibit a subset of GA responses. At the molecular level, BOIs did not significantly alter the stability of a DELLA protein. Instead, BOI and DELLA proteins are targeted to the promoters of a subset of GA-responsive genes and repress their expression. Taken together, our results indicate that the DELLA and BOI proteins inhibit GA responses by interacting with each other, binding to the same promoters of GA-responsive genes, and repressing these genes.
DOI:10.1016/j.molp.2015.08.005URLPMID:26298008 [本文引用: 2]
BOTRYTIS SUSCEPTIBLE1 INTERACTOR (BOI) and its three homologs (BOIs) are RING domain-containing proteins that repress flowering. Here, we investigated how BOIs repress flowering. Genetic analysis of the boiQ quadruple mutant indicates that BOIs repress flowering mainly through FLOWERING LOCUS T (FT). BOIs repress the expression of FT by CONSTANS (CO)-dependent and -independent mechanisms: in the CO-dependent mechanism, BOIs bind to CO, inhibit the targeting of CO to the FT locus, and thus repress the expression of FT; in the CO-independent mechanism, BOIs target the FT locus via a mechanism that requires DELLAs but not CO. This dual repression of FT makes BOIs strong repressors of flowering in both CO-dependent and CO-independent pathways in Arabidopsis thaliana. Our finding that BOIs inhibit CO targeting further suggests that, in addition to modulating CO mRNA expression and CO protein stability, flowering regulation can also modulate the targeting of CO to FT.
DOI:10.1111/jipb.12451URLPMID:26584710 [本文引用: 2]
Flowering is a highly orchestrated and extremely critical process in a plant's life cycle. Previous study has demonstrated that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FLOWERING LOCUS T (FT) integrate the gibberellic acid (GA) signaling pathway and vernalization pathway in regulating flowering time, but detailed molecular mechanisms remain largely unclear. In GA signaling pathway, DELLA proteins are a group of master transcriptional regulators, while in vernalization pathway FLOWERING LOCUS C (FLC) is a core transcriptional repressor that down-regulates the expression of SOC1 and FT. Here, we report that DELLA proteins interact with FLC in vitro and in vivo, and the LHRI domains of DELLAs and the C-terminus of MADS domain of FLC are required for these interactions. Phenotypic and gene expression analysis showed that mutation of FLC reduces while over-expression of FLC enhances the GA response in the flowering process. Further, DELLA-FLC interactions promote the repression ability of FLC on its target genes. In summary, these findings report that the interaction between MADS box transcription factor FLC and GRAS domain regulator DELLAs may integrate various signaling inputs in flowering time control, and shed new light on the regulatory mechanism both for FLC and DELLAs in regulating gene expression.
DOI:10.1111/j.1365-313X.2009.03986.xURLPMID:19656342 [本文引用: 1]
Flowering is controlled by a network of pathways that converge to regulate a small number of floral integrator genes. We studied the interactions in Arabidopsis between three of these integrators, flowering locus T (FT), twin sister of FT (TSF) and suppressor of overexpression of constans 1 (SOC1), as well as their repression by the MADS box transcription factor short vegetative phase (SVP). FT is a mobile signal transmitted from the leaf to the meristem to initiate flowering. Using mRNA null alleles, we show that FT and the closely related TSF are not essential for flowering, but that the double mutant is photoperiod-insensitive. Inactivation of both genes also fully suppresses the early-flowering phenotype caused by over-expression of constans (CO), a transcriptional regulator in the photoperiod pathway. In addition, we demonstrate that TSF and FT have similar biochemical functions by showing that they interact in yeast with the same bZIP transcription factors. Expression of FT or TSF from promoters specific for phloem companion cells drives early flowering of the double mutant, so no expression of either gene is required in the meristem. Furthermore, TSF, like FT, is repressed by SVP, but the triple mutant svp-41 ft-10 tsf-1 expresses SOC1 in the meristem sooner and flowers earlier than ft-10 tsf-1. Thus we distinguish the functions of SVP in repressing FT and TSF in the leaf and SOC1 in the meristem. In addition, a time course of in situ hybridizations suggested that repression of SVP and activation of SOC1 proceed simultaneously in the meristem. These observations clarify the relationships between these early regulators of the floral transition, and further emphasize the relatedness of mechanisms acting in the leaf and meristem to control flowering time.
DOI:10.1111/j.1365-313X.2011.04793.xURLPMID:21950734 [本文引用: 1]
Plants monitor changes in day length to coordinate flowering with favorable seasons to increase their fitness. The day-length specific induction of FLOWERING LOCUS T (FT) regulated by CONSTANS (CO) is the crucial aspect of photoperiodic flowering in Arabidopsis thaliana. Recent studies have elucidated some mechanisms of CO-dependent FT induction. Here, we demonstrate another mechanism of CO-dependent FT regulation. Our results indicate that CO protein partially regulates FT transcription by forming a complex with ASYMMETRIC LEAVES 1 (AS1) protein, which regulates leaf development partly by controlling gibberellin (GA) levels. We identified AS1 as a CO-interacting protein in yeast and verified their interaction in vitro and in planta. We also showed that the temporal and spatial expression pattern of AS1 overlapped with that of CO. In addition, as1 mutants showed GA-independent delayed flowering under different light/dark conditions. FT expression levels in the as1 mutants and the SUC2:CO-HA/as1 line under long-day and 12-h light/12-h dark conditions were reduced compared with wild-type plants and the SUC2:HA-CO line, respectively. Moreover, AS1 bound directly to the specific regions of the FT promoter in vivo. These results indicate that CO forms a functional complex with AS1 to regulate FT expression and that AS1 plays different roles in two regulatory pathways, both of which concomitantly regulate the precise timing of flowering.
DOI:10.1038/nplants.2016.75URLPMID:27255839 [本文引用: 1]
Flowering plants perceive photoperiodic signals in leaves to generate mobile stimuli required for the induction of flower formation at shoot apices. Although FLOWERING LOCUS T (FT) has been identified as part of the mobile floral stimuli in Arabidopsis thaliana, the mechanisms underlying long-distance movement of FT from leaves to shoot apices remain largely unclear. Here we show that a heavy-metal-associated (HMA) domain-containing protein, SODIUM POTASSIUM ROOT DEFECTIVE 1 (NaKR1), is activated by CONSTANS (CO) under long-day conditions and regulates long-distance movement of FT in Arabidopsis. Loss of function of NaKR1 compromises FT transport to shoot apices through sieve elements, causing late flowering under long-day conditions. NaKR1 and FT share similar expression patterns and subcellular localization, and interact with each other in vivo. Grafting experiments demonstrate that NaKR1 promotes flowering through mediating FT translocation from leaves to shoot apices. Thus, photoperiodic control of floral induction requires NaKR1-mediated long-distance delivery of florigenic signals.
DOI:10.1038/nplants.2015.73URL [本文引用: 1]
DOI:10.1038/ncomms11486URLPMID:27139299 [本文引用: 1]
Gibberellins (GAs) are plant hormones that promote a wide range of developmental processes. While GA signalling is well understood, little is known about how GA is transported or how GA distribution is regulated. Here we utilize fluorescently labelled GAs (GA-Fl) to screen for Arabidopsis mutants deficient in GA transport. We show that the NPF3 transporter efficiently transports GA across cell membranes in vitro and GA-Fl in vivo. NPF3 is expressed in root endodermis and repressed by GA. NPF3 is targeted to the plasma membrane and subject to rapid BFA-dependent recycling. We show that abscisic acid (ABA), an antagonist of GA, is also transported by NPF3 in vitro. ABA promotes NPF3 expression and GA-Fl uptake in plants. On the basis of these results, we propose that GA distribution and activity in Arabidopsis is partly regulated by NPF3 acting as an influx carrier and that GA-ABA interaction may occur at the level of transport.
DOI:10.1242/dev.128595URLPMID:26758694 [本文引用: 1]
Flowering in plants is a dynamic and synchronized process where various cues including age, day length, temperature and endogenous hormones fine-tune the timing of flowering for reproductive success. Arabidopsis thaliana is a facultative long day (LD) plant where LD photoperiod promotes flowering. Arabidopsis still flowers under short-day (SD) conditions, albeit much later than in LD conditions. Although factors regulating the inductive LD pathway have been extensively investigated, the non-inductive SD pathway is much less understood. Here, we identified a key basic helix-loop-helix transcription factor called NFL (NO FLOWERING IN SHORT DAY) that is essential to induce flowering specifically under SD conditions in Arabidopsis. nfl mutants do not flower under SD conditions, but flower similar to the wild type under LD conditions. The no-flowering phenotype in SD is rescued either by exogenous application of gibberellin (GA) or by introducing della quadruple mutants in the nfl background, suggesting that NFL acts upstream of GA to promote flowering. NFL is expressed at the meristematic regions and NFL is localized to the nucleus. Quantitative RT-PCR assays using apical tissues showed that GA biosynthetic genes are downregulated and the GA catabolic and receptor genes are upregulated in the nfl mutant compared with the wild type, consistent with the perturbation of the endogenous GA biosynthetic and catabolic intermediates in the mutant. Taken together, these data suggest that NFL is a key transcription factor necessary for promotion of flowering under non-inductive SD conditions through the GA signaling pathway.
DOI:10.1073/pnas.1409567111URLPMID:24979809 [本文引用: 2]
In Arabidopsis thaliana environmental and endogenous cues promote flowering by activating expression of a small number of integrator genes. The MADS box transcription factor SHORT VEGETATIVE PHASE (SVP) is a critical inhibitor of flowering that directly represses transcription of these genes. However, we show by genetic analysis that the effect of SVP cannot be fully explained by repressing known floral integrator genes. To identify additional SVP functions, we analyzed genome-wide transcriptome data and show that GIBBERELLIN 20 OXIDASE 2, which encodes an enzyme required for biosynthesis of the growth regulator gibberellin (GA), is upregulated in svp mutants. GA is known to promote flowering, and we find that svp mutants contain elevated levels of GA that correlate with GA-related phenotypes such as early flowering and organ elongation. The ga20ox2 mutation suppresses the elevated GA levels and partially suppresses the growth and early flowering phenotypes of svp mutants. In wild-type plants, SVP expression in the shoot apical meristem falls when plants are exposed to photoperiods that induce flowering, and this correlates with increased expression of GA20ox2. Mutations that impair the photoperiodic flowering pathway prevent this downregulation of SVP and the strong increase in expression of GA20ox2. We conclude that SVP delays flowering by repressing GA biosynthesis as well as integrator gene expression and that, in response to inductive photoperiods, repression of SVP contributes to the rise in GA at the shoot apex, promoting rapid induction of flowering.
[本文引用: 1]
DOI:10.1242/dev.01206URLPMID:15226253 [本文引用: 3]
Floral initiation and floral organ development are both regulated by the phytohormone gibberellin (GA). For example, in short-day photoperiods, the Arabidopsis floral transition is strongly promoted by GA-mediated activation of the floral meristem-identity gene LEAFY. In addition, anther development and pollen microsporogenesis depend on GA-mediated opposition of the function of specific members of the DELLA family of GA-response repressors. We describe the role of a microRNA (miR159) in the regulation of short-day photoperiod flowering time and of anther development. MiR159 directs the cleavage of mRNA encoding GAMYB-related proteins. These proteins are transcription factors that are thought to be involved in the GA-promoted activation of LEAFY, and in the regulation of anther development. We show that miR159 levels are regulated by GA via opposition of DELLA function, and that both the sequence of miR159 and the regulation of miR159 levels by DELLA are evolutionarily conserved. Finally, we describe the phenotypic consequences of transgenic over-expression of miR159. Increased levels of miR159 cause a reduction in LEAFY transcript levels, delay flowering in short-day photoperiods, and perturb anther development. We propose that miR159 is a phytohormonally regulated homeostatic modulator of GAMYB activity, and hence of GAMYB-dependent developmental processes.
DOI:10.1105/tpc.10.5.791URLPMID:9596637 [本文引用: 1]
The gibberellin class of plant hormones has been implicated in the control of flowering in several species. In Arabidopsis, severe reduction of endogenous gibberellins delays flowering in long days and prevents flowering in short days. We have investigated how the differential effects of gibberellins on flowering correlate with expression of LEAFY, a floral meristem identity gene. We have found that the failure of gibberellin-deficient ga1-3 mutants to flower in short days was paralleled by the absence of LEAFY promoter induction. A causal connection between these two events was confirmed by the ability of a constitutively expressed LEAFY transgene to restore flowering to ga1-3 mutants in short days. In contrast to short days, impairment of gibberellin biosynthesis caused merely a reduction of LEAFY expression when plants were grown in long days or with sucrose in the dark. As a first step toward identifying other small molecules that might regulate flowering, we have developed a rapid in vitro assay for LEAFY promoter activity.
DOI:10.1038/35009125URLPMID:10786797 [本文引用: 1]
Flowering of Arabidopsis is regulated by a daylength-dependent pathway that accelerates flowering in long days and a daylength-independent pathway that ensures flowering in the absence of inductive conditions. These pathways are genetically separable, as there are mutations that delay flowering in long but not short days. Conversely, mutations that block synthesis of the hormone gibberellin abolish flowering in short days, but have on their own only a minor effect in long days. A third pathway, the autonomous pathway, probably acts by modulating the other two pathways. Understanding where and how these pathways are integrated is a prerequisite for understanding why similar environmental or endogenous cues can elicit opposite flowering responses in different plants. In Arabidopsis, floral induction leads ultimately to the upregulation of floral meristem-identity genes such as LEAFY, indicating that floral inductive signals are integrated upstream of LEAFY Here we show that gibberellins activate the LEAFY promoter through cis elements that are different from those that are sufficient for the daylength response, demonstrating that the LEAFY promoter integrates environmental and endogenous signals controlling flowering time.
URLPMID:11743113 [本文引用: 1]
DOI:10.1046/j.1365-313x.2003.01833.xURLPMID:12940954 [本文引用: 2]
The floral transition in Arabidopsis is regulated by at least four flowering pathways: the long-day, autonomous, vernalization, and gibberellin (GA)-dependent pathways. Previously, we reported that the MADS-box transcription factor SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) integrates the long-day and vernalization/autonomous pathways. Here, we present evidences that SOC1 also integrates signaling from the GA-dependent pathway, a major flowering pathway under non-inductive short days. Under short days, the flowering time of GA-biosynthetic and -signaling mutants was well correlated with the level of SOC1 expression; overexpression of SOC1 rescued the non-flowering phenotype of ga1-3, and the soc1 null mutant showed reduced sensitivity to GA for flowering. In addition, we show that vernalization-induced repression of FLOWERING LOCUS C (FLC), an upstream negative regulator of SOC1, is not sufficient to activate SOC1; positive factors are also required. Under short days, the GA pathway provides a positive factor for SOC1 activation. In contrast to SOC1, the GA pathway does not regulate expression of other flowering integrators FLC and FT. Our results explain why the GA pathway has a strong effect on flowering under short days and how vernalization and GA interact at the molecular level.
DOI:10.1074/jbc.M111.337485URLPMID:22431732 [本文引用: 1]
Ambient temperature fluctuates diurnally and seasonally. It profoundly influences the timing of flowering in plants. The floral integrator FLOWERING LOCUS T (FT) mediates ambient temperature signals via the thermosensory pathway in Arabidopsis flowering. microRNA172 (miR172), which promotes flowering by inducing FT, also responds to changes in ambient temperature. However, it is largely unknown how miR172 integrates ambient temperature signals into the flowering genetic network. Here, we show that Arabidopsis RNA-binding protein FCA promotes the processing of primary microRNA172 transcripts (pri-miR172) in response to changes in ambient temperature. Ambient temperature regulates miR172 biogenesis primarily at the pri-miR172 processing step. miR172 abundance is elevated at 23 degrees C but not at 16 degrees C. miR172 accumulation at 23 degrees C requires functional FCA. FCA binds to the flanking sequences of the stem-loop within the pri-miR172 transcripts via the RNA recognition motif. FCA also binds to the primary transcripts of other temperature-responsive miRNAs, such as miR398 and miR399. Notably, levels of FCA mRNAs and proteins increase at 23 degrees C but remain low at 16 degrees C, supporting the role of FCA in temperature perception. Our data show that FCA regulation of miR172 processing is an early event in the thermosensory flowering pathway. We propose that the FCA-miR172 regulon provides an adaptive strategy that fine tunes the onset of flowering under fluctuating ambient temperature conditions.
[本文引用: 2]
[本文引用: 2]
DOI:10.1016/j.cell.2009.06.014URLPMID:19703399 [本文引用: 1]
The FT gene integrates several external and endogenous cues controlling flowering, including information on day length. A complex of the mobile FT protein and the bZIP transcription factor FD in turn has a central role in activating genes that execute the switch from vegetative to reproductive development. Here we reveal that microRNA156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes not only act downstream of FT/FD, but also define a separate endogenous flowering pathway. High levels of miR156 in young plants prevent precocious flowering. A subsequent day length-independent decline in miR156 abundance provides a permissive environment for flowering and is paralleled by a rise in SPL levels. At the shoot apex, FT/FD and SPLs converge on an overlapping set of targets, with SPLs directly activating flower-promoting MADS box genes, providing a molecular substrate for both the redundant activities and the feed-forward action of the miR156/SPL and FT/FD modules in flowering control.
DOI:10.1016/j.cell.2009.06.031URLPMID:19703400 [本文引用: 1]
The transition from the juvenile to the adult phase of shoot development in plants is accompanied by changes in vegetative morphology and an increase in reproductive potential. Here, we describe the regulatory mechanism of this transition. We show that miR156 is necessary and sufficient for the expression of the juvenile phase, and regulates the timing of the juvenile-to-adult transition by coordinating the expression of several pathways that control different aspects of this process. miR156 acts by repressing the expression of functionally distinct SPL transcription factors. miR172 acts downstream of miR156 to promote adult epidermal identity. miR156 regulates the expression of miR172 via SPL9 which, redundantly with SPL10, directly promotes the transcription of miR172b. Thus, like the larval-to-adult transition in Caenorhabditis elegans, the juvenile-to-adult transition in Arabidopsis is mediated by sequentially operating miRNAs. miR156 and miR172 are positively regulated by the transcription factors they target, suggesting that negative feedback loops contribute to the stability of the juvenile and adult phases.
DOI:10.1016/j.devcel.2016.04.001URLPMID:27134142 [本文引用: 4]
Flowering is initiated in response to environmental and internal cues that are integrated at the shoot apical meristem (SAM). We show that SPL15 coordinates the basal floral promotion pathways required for flowering of Arabidopsis in non-inductive environments. SPL15 directly activates transcription of the floral regulators FUL and miR172b in the SAM during floral induction, whereas its paralog SPL9 is expressed later on the flanks of the SAM. The capacity of SPL15 to promote flowering is regulated by age through miR156, which targets SPL15 mRNA, and gibberellin (GA), which releases SPL15 from DELLAs. Furthermore, SPL15 and the MADS-box protein SOC1 cooperate to promote transcription of their target genes. SPL15 recruits RNAPII and MED18, a Mediator complex component, in a GA-dependent manner, while SOC1 facilitates active chromatin formation with the histone demethylase REF6. Thus, we present a molecular basis for assimilation of flowering signals and transcriptional control at the SAM during flowering.
DOI:10.1104/pp.16.01471URLPMID:28057895 [本文引用: 1]
PICKLE (PKL) is an ATP-dependent chromodomain-helicase-DNA-binding domain (CHD3) chromatin remodeling enzyme in Arabidopsis (Arabidopsis thaliana). Previous studies showed that PKL promotes embryonic-to-vegetative transition by inhibiting expression of seed-specific genes during seed germination. The pkl mutants display a low penetrance of the
DOI:10.1105/tpc.113.121848URL [本文引用: 1]
Plant cell elongation is controlled by endogenous hormones, including brassinosteroid (BR) and gibberellin (GA), and by environmental factors, such as light/darkness. The molecular mechanisms underlying the convergence of these signals that govern cell growth remain largely unknown. We previously showed that the chromatin-remodeling factor PICKLE/ENHANCED PHOTOMORPHOGENIC1 (PKL/EPP1) represses photomorphogenesis in Arabidopsis thaliana. Here, we demonstrated that PKL physically interacted with PHYTOCHROME-INTERACTING FACTOR3 (PIF3) and BRASSINAZOLE-RESISTANT1 (BZR1), key components of the light and BR signaling pathways, respectively. Also, this interaction promoted the association of PKL with cell elongation-related genes. We found that PKL, PIF3, and BZR1 coregulate skotomorphogenesis by repressing the trimethylation of histone H3 Lys-27 (H3K27me3) on target promoters. Moreover, DELLA proteins interacted with PKL and attenuated its binding ability. Strikingly, brassinolide and GA(3) inhibited H3K27me3 modification of histones associated with cell elongation-related loci in a BZR1- and DELLA-mediated manner, respectively. Our findings reveal that the PKL chromatin-remodeling factor acts as a critical node that integrates light/darkness, BR, and GA signals to epigenetically regulate plant growth and development. This work also provides a molecular framework by which hormone signals regulate histone modification in concert with light/dark environmental cues.
DOI:10.1016/j.devcel.2005.01.018URLPMID:15809034 [本文引用: 1]
Most plant microRNAs (miRNAs) have perfect or near-perfect complementarity with their targets. This is consistent with their primary mode of action being cleavage of target mRNAs, similar to that induced by perfectly complementary small interfering RNAs (siRNAs). However, there are natural targets with up to five mismatches. Furthermore, artificial siRNAs can have substantial effects on so-called off-targets, to which they have only limited complementarity. By analyzing the transcriptome of plants overexpressing different miRNAs, we have deduced a set of empirical parameters for target recognition. Compared to artificial siRNAs, authentic plant miRNAs appear to have much higher specificity, which may reflect their coevolution with the remainder of the transcriptome. We also demonstrate that miR172, previously thought to act primarily by translational repression, can efficiently guide mRNA cleavage, although the effects on steady-state levels of target transcripts are obscured by strong feedback regulation. This finding unifies the view of plant miRNA action.
DOI:10.1371/journal.pgen.1006263URLPMID:27541584 [本文引用: 2]
Correct developmental timing is essential for plant fitness and reproductive success. Two important transitions in shoot development-the juvenile-to-adult vegetative transition and the vegetative-to-reproductive transition-are mediated by a group of genes targeted by miR156, SQUAMOSA PROMOTER BINDING PROTEIN (SBP) genes. To determine the developmental functions of these genes in Arabidopsis thaliana, we characterized their expression patterns, and their gain-of-function and loss-of-function phenotypes. Our results reveal that SBP-LIKE (SPL) genes in Arabidopsis can be divided into three functionally distinct groups: 1) SPL2, SPL9, SPL10, SPL11, SPL13 and SPL15 contribute to both the juvenile-to-adult vegetative transition and the vegetative-to-reproductive transition, with SPL9, SP13 and SPL15 being more important for these processes than SPL2, SPL10 and SPL11; 2) SPL3, SPL4 and SPL5 do not play a major role in vegetative phase change or floral induction, but promote the floral meristem identity transition; 3) SPL6 does not have a major function in shoot morphogenesis, but may be important for certain physiological processes. We also found that miR156-regulated SPL genes repress adventitious root development, providing an explanation for the observation that the capacity for adventitious root production declines as the shoot ages. miR156 is expressed at very high levels in young seedlings, and declines in abundance as the shoot develops. It completely blocks the expression of its SPL targets in the first two leaves of the rosette, and represses these genes to different degrees at later stages of development, primarily by promoting their translational repression. These results provide a framework for future studies of this multifunctional family of transcription factors, and offer new insights into the role of miR156 in Arabidopsis development.
DOI:10.1126/science.1250498URLPMID:24812402 [本文引用: 1]
The switch to reproductive development is biphasic in many plants, a feature important for optimal pollination and yield. We show that dual opposite roles of the phytohormone gibberellin underpin this phenomenon in Arabidopsis. Although gibberellin promotes termination of vegetative development, it inhibits flower formation. To overcome this effect, the transcription factor LEAFY induces expression of a gibberellin catabolism gene; consequently, increased LEAFY activity causes reduced gibberellin levels. This allows accumulation of gibberellin-sensitive DELLA proteins. The DELLA proteins are recruited by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE transcription factors to regulatory regions of the floral commitment gene APETALA1 and promote APETALA1 up-regulation and floral fate synergistically with LEAFY. The two opposing functions of gibberellin may facilitate evolutionary and environmental modulation of plant inflorescence architecture.
DOI:10.1105/tpc.000679URL [本文引用: 1]
DOI:10.1007/s00425-001-0688-yURLPMID:11925032 [本文引用: 1]
Jasmonates are naturally occurring signal compounds that regulate plant growth and development, and are involved in plant responses to several environmental stress factors. The mode of action of jasmonates has been investigated traditionally by analysis of the effects of exogenous application of these compounds, including identification of jasmonate-responsive genes and determination of their expression and responsive promoter elements. In addition, jasmonate biosynthesis has been studied by identification of biosynthetic enzymes, use of inhibitors and determination of endogenous jasmonate levels. Recently, several mutants defective in jasmonate biosynthesis and signaling have been isolated and their phenotypes shed new light on the role of jasmonates and jasmonate signaling in plant responses to pathogens, insects and ozone.
DOI:10.1104/pp.111.184275URLPMID:21994348 [本文引用: 1]
The molecular mechanism of how the histone deacetylase HDA6 participates in maintaining transposable element (TE) silencing in Arabidopsis (Arabidopsis thaliana) is not yet defined. In this study, we show that a subset of TEs was transcriptionally reactivated and that TE reactivation was associated with elevated histone H3 and H4 acetylation as well as increased H3K4Me3 and H3K4Me2 in hda6 mutants. Decreased DNA methylation of the TEs was also detected in hda6 mutants, suggesting that HDA6 silences the TEs by regulating histone acetylation and methylation as well as the DNA methylation status of the TEs. Similarly, transcripts of some of these TEs were also increased in the methyltransferase1 (met1) mutant, with decreased DNA methylation. Furthermore, H4 acetylation, H3K4Me3, H3K4Me2, and H3K36Me2 were enriched at the coregulated TEs in the met1 and hda6 met1 mutants. Protein-protein interaction analysis indicated that HDA6 physically interacts with MET1 in vitro and in vivo, and further deletion analysis demonstrated that the carboxyl-terminal region of HDA6 and the bromo-adjacent homology domain of MET1 were responsible for the interaction. These results suggested that HDA6 and MET1 interact directly and act together to silence TEs by modulating DNA methylation, histone acetylation, and histone methylation status.
DOI:10.1104/pp.111.174417URL [本文引用: 1]
Histone acetylation and deacetylation play an important role in epigenetic controls of gene expression. HISTONE DEACETYLASE6 (HDA6) is a REDUCED POTASSIUM DEPENDENCY3-type histone deacetylase, and the Arabidopsis (Arabidopsis thaliana) hda6 mutant axe1-5 displayed a late-flowering phenotype. axe1-5/flc-3 double mutants flowered earlier than axe1-5 plants, indicating that the late-flowering phenotype of axe1-5 was FLOWERING LOCUS C (FLC) dependent. Bimolecular fluorescence complementation, in vitro pull-down, and coimmunoprecipitation assays revealed the protein-protein interaction between HDA6 and the histone demethylase FLD. It was found that the SWIRM domain in the amino-terminal region of FLD and the carboxyl-terminal region of HDA6 are responsible for the interaction between these two proteins. Increased levels of histone H3 acetylation and H3K4 trimethylation at FLC, MAF4, and MAF5 were found in both axe1-5 and fld-6 plants, suggesting functional interplay between histone deacetylase and demethylase in flowering control. These results support a scenario in which histone deacetylation and demethylation cross talk are mediated by physical association between HDA6 and FLD. Chromatin immunoprecipitation analysis indicated that HDA6 bound to the chromatin of several potential target genes, including FLC and MAF4. Genome-wide gene expression analysis revealed that, in addition to genes related to flowering, genes involved in gene silencing and stress response were also affected in hda6 mutants, revealing multiple functions of HDA6. Furthermore, a subset of transposons was up-regulated and displayed increased histone hyperacetylation, suggesting that HDA6 can also regulate transposons through deacetylating histone.
DOI:10.1126/science.1091109URLPMID:14593187 [本文引用: 1]
The Arabidopsis autonomous floral-promotion pathway promotes flowering independently of the photoperiod and vernalization pathways by repressing FLOWERING LOCUS C (FLC), a MADS-box transcription factor that blocks the transition from vegetative to reproductive development. Here, we report that FLOWERING LOCUS D (FLD), one of six genes in the autonomous pathway, encodes a plant homolog of a protein found in histone deacetylase complexes in mammals. Lesions in FLD result in hyperacetylation of histones in FLC chromatin, up-regulation of FLC expression, and extremely delayed flowering. Thus, the autonomous pathway regulates flowering in part by histone deacetylation. However, not all autonomous-pathway mutants exhibit FLC hyperacetylation, indicating that multiple means exist by which this pathway represses FLC expression.
DOI:10.1105/tpc.010192URLPMID:11595796 [本文引用: 1]
The Arabidopsis mutant defective in anther dehiscence1 (dad1) shows defects in anther dehiscence, pollen maturation, and flower opening. The defects were rescued by the exogenous application of jasmonic acid (JA) or linolenic acid, which is consistent with the reduced accumulation of JA in the dad1 flower buds. We identified the DAD1 gene by T-DNA tagging, which is characteristic to a putative N-terminal transit peptide and a conserved motif found in lipase active sites. DAD1 protein expressed in Escherichia coli hydrolyzed phospholipids in an sn-1-specific manner, and DAD1-green fluorescent protein fusion protein expressed in leaf epidermal cells localized predominantly in chloroplasts. These results indicate that the DAD1 protein is a chloroplastic phospholipase A1 that catalyzes the initial step of JA biosynthesis. DAD1 promoter::beta-glucuronidase analysis revealed that the expression of DAD1 is restricted in the stamen filaments. A model is presented in which JA synthesized in the filaments regulates the water transport in stamens and petals.
DOI:10.1111/j.1469-8137.2012.04329.xURL [本文引用: 1]
Understanding the processes that underlie pollen release is a prime target for controlling fertility to enable selective breeding and the efficient production of hybrid crops. Pollen release requires anther opening, which involves changes in the biomechanical properties of the anther wall. In this research, we develop and use a mathematical model to understand how these biomechanical processes lead to anther opening.
Our mathematical model describing the biomechanics of anther opening incorporates the bilayer structure of the mature anther wall, which comprises the outer epidermal cell layer, whose turgor pressure is related to its hydration, and the endothecial layer, whose walls contain helical secondary thickening, which resists stretching and bending. The model describes how epidermal dehydration, in association with the thickened endothecial layer, creates forces within the anther wall causing it to bend outwards, resulting in anther opening and pollen release.
The model demonstrates that epidermal dehydration can drive anther opening, and suggests why endothecial secondary thickening is essential for this process (explaining the phenotypes presented in the myb26 and nst1nst2 mutants).
The research hypothesizes and demonstrates a biomechanical mechanism for anther opening, which appears to be conserved in many other biological situations where tissue movement occurs.
DOI:10.1242/dev.01955URLPMID:16107481 [本文引用: 3]
Pollination in flowering plants requires that anthers release pollen when the gynoecium is competent to support fertilization. We show that in Arabidopsis thaliana, two paralogous auxin response transcription factors, ARF6 and ARF8, regulate both stamen and gynoecium maturation. arf6 arf8 double-null mutant flowers arrested as infertile closed buds with short petals, short stamen filaments, undehisced anthers that did not release pollen and immature gynoecia. Numerous developmentally regulated genes failed to be induced. ARF6 and ARF8 thus coordinate the transition from immature to mature fertile flowers. Jasmonic acid (JA) measurements and JA feeding experiments showed that decreased jasmonate production caused the block in pollen release, but not the gynoecium arrest. The double mutant had altered auxin responsive gene expression. However, whole flower auxin levels did not change during flower maturation, suggesting that auxin might regulate flower maturation only under specific environmental conditions, or in localized organs or tissues of flowers. arf6 and arf8 single mutants and sesquimutants (homozygous for one mutation and heterozygous for the other) had delayed stamen development and decreased fecundity, indicating that ARF6 and ARF8 gene dosage affects timing of flower maturation quantitatively.
DOI:10.1016/j.molcel.2004.05.027URLPMID:15200956 [本文引用: 1]
MicroRNAs (miRNAs) are approximately 21-nucleotide RNAs, some of which have been shown to play important gene-regulatory roles during plant development. We developed comparative genomic approaches to systematically identify both miRNAs and their targets that are conserved in Arabidopsis thaliana and rice (Oryza sativa). Twenty-three miRNA candidates, representing seven newly identified gene families, were experimentally validated in Arabidopsis, bringing the total number of reported miRNA genes to 92, representing 22 families. Nineteen newly identified target candidates were confirmed by detecting mRNA fragments diagnostic of miRNA-directed cleavage in plants. Overall, plant miRNAs have a strong propensity to target genes controlling development, particularly those of transcription factors and F-box proteins. However, plant miRNAs have conserved regulatory functions extending beyond development, in that they also target superoxide dismutases, laccases, and ATP sulfurylases. The expression of miR395, the sulfurylase-targeting miRNA, increases upon sulfate starvation, showing that miRNAs can be induced by environmental stress.
DOI:10.1105/tpc.108.064758URLPMID:19820192 [本文引用: 1]
The development of shoot-borne roots, or adventitious roots, is indispensable for mass propagation of elite genotypes. It is a complex genetic trait with a high phenotypic plasticity due to multiple endogenous and environmental regulatory factors. We demonstrate here that a subtle balance of activator and repressor AUXIN RESPONSE FACTOR (ARF) transcripts controls adventitious root initiation. Moreover, microRNA activity appears to be required for fine-tuning of this process. Thus, ARF17, a target of miR160, is a negative regulator, and ARF6 and ARF8, targets of miR167, are positive regulators of adventitious rooting. The three ARFs display overlapping expression domains, interact genetically, and regulate each other's expression at both transcriptional and posttranscriptional levels by modulating miR160 and miR167 availability. This complex regulatory network includes an unexpected feedback regulation of microRNA homeostasis by direct and nondirect target transcription factors. These results provide evidence of microRNA control of phenotypic variability and are a significant step forward in understanding the molecular mechanisms regulating adventitious rooting.
DOI:10.1105/tpc.15.00619URLPMID:26410299 [本文引用: 2]
Flowering time of plants must be tightly regulated to maximize reproductive success. Plants have evolved sophisticated signaling network to coordinate the timing of flowering in response to their ever-changing environmental conditions. Besides being a key immune signal, the lipid-derived plant hormone jasmonate (JA) also regulates a wide range of developmental processes including flowering time. Here, we report that the CORONATINE INSENSITIVE1 (COI1)-dependent signaling pathway delays the flowering time of Arabidopsis thaliana by inhibiting the expression of the florigen gene FLOWERING LOCUS T (FT). We provide genetic and biochemical evidence that the APETALA2 transcription factors (TFs) TARGET OF EAT1 (TOE1) and TOE2 interact with a subset of JAZ (jasmonate-ZIM domain) proteins and repress the transcription of FT. Our results support a scenario that, when plants encounter stress conditions, bioactive JA promotes COI1-dependent degradation of JAZs. Degradation of the JAZ repressors liberates the transcriptional function of the TOEs to repress the expression of FT and thereby triggers the signaling cascades to delay flowering. Our study identified interacting pairs of TF and JAZ transcriptional regulators that underlie JA-mediated regulation of flowering, suggesting that JA signals are converted into specific context-dependent responses by matching pairs of TF and JAZ proteins.
DOI:10.1042/bse0580029URLPMID:26374885 [本文引用: 1]
The phytohormone abscisic acid (ABA) plays crucial roles in numerous physiological processes during plant growth and abiotic stress responses. The endogenous ABA level is controlled by complex regulatory mechanisms involving biosynthesis, catabolism, transport and signal transduction pathways. This complex regulatory network may target multiple levels, including transcription, translation and post-translational regulation of genes involved in ABA responses. Most of the genes involved in ABA biosynthesis, catabolism and transport have been characterized. The local ABA concentration is critical for initiating ABA-mediated signalling during plant development and in response to environmental changes. In this chapter we discuss the mechanisms that regulate ABA biosynthesis, catabolism, transport and homoeostasis. We also present the findings of recent research on ABA perception by cellular receptors, and ABA signalling in response to cellular and environmental conditions.
DOI:10.1093/jxb/eri206URLPMID:15983017 [本文引用: 1]
Much of the literature on the phytohormone abscisic acid (ABA) describes it as a mediator in triggering plant responses to environmental stimuli, as well as a growth inhibitor. ABA-deficient mutants, however, display a stunted phenotype even under well-watered conditions and high relative humidity, which suggests that growth promotion may also be one of the roles of endogenous ABA. Zeaxanthin epoxidase, the product of the ABA1 gene of Arabidopsis thaliana, catalyses the epoxidation of zeaxanthin to antheraxanthin and violaxanthin, generating the epoxycarotenoid precursor of the ABA biosynthetic pathway. This paper gives a description of the molecular and phenotypic characterization of a large series of mutant alleles of the ABA1 gene, which cause different degrees of ABA deficiency, four of them previously isolated (aba1-1, aba1-3, aba1-4, and aba1-6) and the remaining five novel (san1-1, san1-2, san1-3, san1-4, and sre3). Molecular analysis of these alleles provides insights into the domains in which they compromise zeaxanthin epoxidase function. The size of the leaves, inflorescences, and flowers of these mutants is reduced, and their rosettes have lower fresh and dry weights than their wild types, as a result of a diminished cell size. Low concentrations of exogenous ABA increase the fresh weight of mutant and wild-type plants, as well as the dry weight of the mutants. The leaves of aba1 mutants are abnormally shaped and fail to develop clearly distinct spongy and palisade mesophyll layers. Taken together, these phenotypic traits indicate, as suggested by previous authors, that ABA acts as a growth promoter during vegetative development. The abnormal shape and internal structure of the leaves of aba1 mutants suggests, in addition, a role for ABA in organogenesis.
DOI:10.7554/eLife.13768URLPMID:27697148 [本文引用: 1]
Drought inhibits plant growth and can also induce premature senescence. Here we identify a transcription factor, ABA INSENSITIVE GROWTH 1 (ABIG1) required for abscisic acid (ABA) mediated growth inhibition, but not for stomatal closure. ABIG1 mRNA levels are increased both in response to drought and in response to ABA treatment. When treated with ABA, abig1 mutants remain greener and produce more leaves than comparable wild-type plants. When challenged with drought, abig1 mutants have fewer yellow, senesced leaves than wild-type. Induction of ABIG1 transcription mimics ABA treatment and regulates a set of genes implicated in stress responses. We propose a model in which drought acts through ABA to increase ABIG1 transcription which in turn restricts new shoot growth and promotes leaf senescence. The results have implications for plant breeding: the existence of a mutant that is both ABA resistant and drought resistant points to new strategies for isolating drought resistant genetic varieties.
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DOI:10.1371/journal.pone.0014012URLPMID:21103336 [本文引用: 1]
BACKGROUND: Genetic interactions between phytohormones in the control of flowering time in Arabidopsis thaliana have not been extensively studied. Three phytohormones have been individually connected to the floral-timing program. The inductive function of gibberellins (GAs) is the most documented. Abscisic acid (ABA) has been demonstrated to delay flowering. Finally, the promotive role of brassinosteroids (BRs) has been established. It has been reported that for many physiological processes, hormone pathways interact to ensure an appropriate biological response. METHODOLOGY: We tested possible genetic interactions between GA-, ABA-, and BR-dependent pathways in the control of the transition to flowering. For this, single and double mutants deficient in the biosynthesis of GAs, ABA, and BRs were used to assess the effect of hormone deficiency on the timing of floral transition. Also, plants that over-express genes encoding rate-limiting enzymes in each biosynthetic pathway were generated and the flowering time of these lines was investigated. CONCLUSIONS: Loss-of-function studies revealed a complex relationship between GAs and ABA, and between ABA and BRs, and suggested a cross-regulatory relation between GAs to BRs. Gain-of-function studies revealed that GAs were clearly limiting in their sufficiency of action, whereas increases in BRs and ABA led to a more modest phenotypic effect on floral timing. We conclude from our genetic tests that the effects of GA, ABA, and BR on timing of floral induction are only in partially coordinated action.
DOI:10.2503/jjshs.64.9URL [本文引用: 1]
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DOI:10.1104/pp.113.217729URL [本文引用: 2]
Modulation of the transition to flowering plays an important role in the adaptation to drought. The drought-escape (DE) response allows plants to adaptively shorten their life cycle to make seeds before severe stress leads to death. However, the molecular basis of the DE response is unknown. A screen of different Arabidopsis (Arabidopsis thaliana) flowering time mutants under DE-triggering conditions revealed the central role of the flower-promoting gene GIGANTEA (GI) and the florigen genes FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF) in the DE response. Further screens showed that the phytohormone abscisic acid is required for the DE response, positively regulating flowering under long-day conditions. Drought stress promotes the transcriptional up-regulation of the florigens in an abscisic acid- and photoperiod-dependent manner, so that early flowering only occurs under long days. Along with the florigens, the floral integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 is also up-regulated in a similar fashion and contributes to the activation of TSF. The DE response was recovered under short days in the absence of the floral repressor SHORT VEGETATIVE PHASE or in GI-overexpressing plants. Our data reveal a key role for GI in connecting photoperiodic cues and environmental stress independently from the central FT/TSF activator CONSTANS. This mechanism explains how environmental cues may act upon the florigen genes in a photoperiodically controlled manner, thus enabling plastic flowering responses.
DOI:10.1093/jxb/erw384URLPMID:27733440 [本文引用: 3]
One strategy deployed by plants to endure water scarcity is to accelerate the transition to flowering adaptively via the drought escape (DE) response. In Arabidopsis thaliana, activation of the DE response requires the photoperiodic response gene GIGANTEA (GI) and the florigen genes FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF). The phytohormone abscisic acid (ABA) is also required for the DE response, by promoting the transcriptional up-regulation of the florigen genes. The mode of interaction between ABA and the photoperiodic genes remains obscure. In this work we use a genetic approach to demonstrate that ABA modulates GI signalling and consequently its ability to activate the florigen genes. We also reveal that the ABA-dependent activation of FT, but not TSF, requires CONSTANS (CO) and that impairing ABA signalling dramatically reduces the expression of florigen genes with little effect on the CO transcript profile. ABA signalling thus has an impact on the core genes of photoperiodic signalling GI and CO by modulating their downstream function and/or activities rather than their transcript accumulation. In addition, we show that as well as promoting flowering, ABA simultaneously represses flowering, independent of the florigen genes. Genetic analysis indicates that the target of the repressive function of ABA is the flowering-promoting gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), a transcription factor integrating floral cues in the shoot meristem. Our study suggests that variations in ABA signalling provide different developmental information that allows plants to co-ordinate the onset of the reproductive phase according to the available water resources.
DOI:10.1074/jbc.275.3.1723URLPMID:10636868 [本文引用: 1]
Abscisic acid (ABA) plays an important role in environmental stress responses of higher plants during vegetative growth. One of the ABA-mediated responses is the induced expression of a large number of genes, which is mediated by cis-regulatory elements known as abscisic acid-responsive elements (ABREs). Although a number of ABRE binding transcription factors have been known, they are not specifically from vegetative tissues under induced conditions. Considering the tissue specificity of ABA signaling pathways, factors mediating ABA-dependent stress responses during vegetative growth phase may thus have been unidentified so far. Here, we report a family of ABRE binding factors isolated from young Arabidopsis plants under stress conditions. The factors, isolated by a yeast one-hybrid system using a prototypical ABRE and named as ABFs (ABRE binding factors) belong to a distinct subfamily of bZIP proteins. Binding site selection assay performed with one ABF showed that its preferred binding site is the strong ABRE, CACGTGGC. ABFs can transactivate an ABRE-containing reporter gene in yeast. Expression of ABFs is induced by ABA and various stress treatments, whereas their induction patterns are different from one another. Thus, a new family of ABRE binding factors indeed exists that have the potential to activate a large number of ABA/stress-responsive genes in Arabidopsis.
DOI:10.1073/pnas.190309197URLPMID:11005831 [本文引用: 1]
The induction of the dehydration-responsive Arabidopsis gene, rd29B, is mediated mainly by abscisic acid (ABA). Promoter analysis of rd29B indicated that two ABA-responsive elements (ABREs) are required for the dehydration-responsive expression of rd29B as cis-acting elements. Three cDNAs encoding basic leucine zipper (bZIP)-type ABRE-binding proteins were isolated by using the yeast one-hybrid system and were designated AREB1, AREB2, and AREB3 (ABA-responsive element binding protein). Transcription of the AREB1 and AREB2 genes is up-regulated by drought, NaCl, and ABA treatment in vegetative tissues. In a transient transactivation experiment using Arabidopsis leaf protoplasts, both the AREB1 and AREB2 proteins activated transcription of a reporter gene driven by ABRE. AREB1 and AREB2 required ABA for their activation, because their transactivation activities were repressed in aba2 and abi1 mutants and enhanced in an era1 mutant. Activation of AREBs by ABA was suppressed by protein kinase inhibitors. These results suggest that both AREB1 and AREB2 function as transcriptional activators in the ABA-inducible expression of rd29B, and further that ABA-dependent posttranscriptional activation of AREB1 and AREB2, probably by phosphorylation, is necessary for their maximum activation by ABA. Using cultured Arabidopsis cells, we demonstrated that a specific ABA-activated protein kinase of 42-kDa phosphorylated conserved N-terminal regions in the AREB proteins.
DOI:10.1105/tpc.106.048538URLPMID:17307925 [本文引用: 1]
Abscisic acid (ABA) is an important phytohormone regulating various plant processes, including seed germination. Although phosphorylation has been suggested to be important, the protein kinases required for ABA signaling during seed germination and seedling growth remain elusive. Here, we show that two protein kinases, SNF1-RELATED PROTEIN KINASE2.2 (SnRK2.2) and SnRK2.3, control responses to ABA in seed germination, dormancy, and seedling growth in Arabidopsis thaliana. A snrk2.2 snrk2.3 double mutant, but not snrk2.2 or snrk2.3 single mutants, showed strong ABA-insensitive phenotypes in seed germination and root growth inhibition. Changes in seed dormancy and ABA-induced Pro accumulation consistent with ABA insensitivity were also observed. The snrk2.2 snrk2.3 double mutant had a greatly reduced level of a 42-kD kinase activity capable of phosphorylating peptides from ABF (for ABA Response Element Binding Factor) transcription factors. ABA-induced expression of several genes whose promoters contain an ABA response element (ABRE) was reduced in snrk2.2 snrk2.3, suggesting that the mechanism of SnRK2.2 and SnRK2.3 action in ABA signaling involves the activation of ABRE-driven gene expression through the phosphorylation of ABFs. Together, these results demonstrate that SnRK2.2 and SnRK2.3 are redundant but key protein kinases that mediate a major part of ABA signaling in Arabidopsis.
DOI:10.1093/pcp/pcp147URLPMID:19880399 [本文引用: 1]
Responses to water stress are thought to be mediated by transcriptional regulation of gene expression via reversible protein phosphorylation events. Previously, we reported that bZIP (basic-domain leucine zipper)-type AREB/ABF (ABA-responsive element-binding protein/factor) transcription factors are involved in ABA signaling under water stress conditions in Arabidopsis. The AREB1 protein is phosphorylated in vitro by ABA-activated SNF1-related protein kinase 2s (SnRK2s) such as SRK2D/SnRK2.2, SRK2E/SnRK2.6 and SRK2I/SnRK2.3 (SRK2D/E/I). Consistent with this, we now show that SRK2D/E/I and AREB1 co-localize and interact in nuclei in planta. Our results show that unlike srk2d, srk2e and srk2i single and double mutants, srk2d srk2e srk2i (srk2d/e/i) triple mutants exhibit greatly reduced tolerance to drought stress and highly enhanced insensitivity to ABA. Under water stress conditions, ABA- and water stress-dependent gene expression, including that of transcription factors, is globally and drastically impaired, and jasmonic acid (JA)-responsive and flowering genes are up-regulated in srk2d/e/i triple mutants, but not in other single and double mutants. The down-regulated genes in srk2d/e/i and areb/abf triple mutants largely overlap in ABA-dependent expression, supporting the view that SRK2D/E/I regulate AREB/ABFs in ABA signaling in response to water stress. Almost all dehydration-responsive LEA (late embryogenesis abundant) protein genes and group-A PP2C (protein phosphatase 2C) genes are strongly down-regulated in the srk2d/e/i triple mutants. Further, our data show that these group-A PP2Cs, such as HAI1 and ABI1, interact with SRK2D. Together, our results indicate that SRK2D/E/I function as main positive regulators, and suggest that ABA signaling is controlled by the dual modulation of SRK2D/E/I and group-A PP2Cs.
DOI:10.1111/pce.12351URLPMID:24738645 [本文引用: 2]
Under osmotic stress conditions such as drought and high salinity, the plant hormone abscisic acid (ABA) plays important roles in stress-responsive gene expression mainly through three bZIP transcription factors, AREB1/ABF2, AREB2/ABF4 and ABF3, which are activated by SNF1-related kinase 2s (SnRK2s) such as SRK2D/SnRK2.2, SRK2E/SnRK2.6 and SRK2I/SnRK2.3 (SRK2D/E/I). However, since the three AREB/ABFs are crucial, but not exclusive, for the SnRK2-mediated gene expression, transcriptional pathways governed by SRK2D/E/I are not fully understood. Here, we show that a bZIP transcription factor, ABF1, is a functional homolog of AREB1, AREB2 and ABF3 in ABA-dependent gene expression in Arabidopsis. Despite lower expression levels of ABF1 than those of the three AREB/ABFs, the areb1 areb2 abf3 abf1 mutant plants displayed increased sensitivity to drought and decreased sensitivity to ABA in primary root growth compared with the areb1 areb2 abf3 mutant. Genome-wide transcriptome analyses revealed that expression of downstream genes of SRK2D/E/I, which include many genes functioning in osmotic stress responses and tolerance such as transcription factors and LEA proteins, was mostly impaired in the quadruple mutant. Thus, these results indicate that the four AREB/ABFs are the predominant transcription factors downstream of SRK2D/E/I in ABA signalling in response to osmotic stress during vegetative growth.
DOI:10.1073/pnas.1118876109URLPMID:22334645 [本文引用: 1]
Many plants monitor day-length changes throughout the year and use the information to precisely regulate the timing of seasonal flowering for maximum reproductive success. In Arabidopsis thaliana, transcriptional regulation of the CONSTANS (CO) gene and posttranslational regulation of CO protein are crucial mechanisms for proper day-length measurement in photoperiodic flowering. Currently, the CYCLING DOF FACTOR proteins are the only transcription factors known to directly regulate CO gene expression, and the mechanisms that directly activate CO transcription have remained unknown. Here we report the identification of four CO transcriptional activators, named FLOWERING BHLH 1 (FBH1), FBH2, FBH3, and FBH4. All FBH proteins are related basic helix-loop-helix-type transcription factors that preferentially bind to the E-box cis-elements in the CO promoter. Overexpression of all FBH genes drastically elevated CO levels and caused early flowering regardless of photoperiod, whereas CO levels were reduced in the fbh quadruple mutants. In addition, FBH1 is expressed in the vascular tissue and bound near the transcription start site of the CO promoter in vivo. Furthermore, FBH homologs in poplar and rice induced CO expression in Arabidopsis. These results indicate that FBH proteins positively regulate CO transcription for photoperiodic flowering and that this mechanism may be conserved in diverse plant species. Our results suggest that the diurnal CO expression pattern is generated by a concert of redundant functions of positive and negative transcriptional regulators.
DOI:10.1105/tpc.108.065433URLPMID:19717618 [本文引用: 1]
The phytohormone gibberellic acid (GA) regulates diverse aspects of plant growth and development. GA responses are triggered by the degradation of DELLA proteins, which function as repressors in GA signaling pathways. Recent studies in Arabidopsis thaliana and rice (Oryza sativa) have implied that the degradation of DELLA proteins occurred via the ubiquitin-proteasome system. Here, we developed an Arabidopsis cell-free system to recapitulate DELLA protein degradation in vitro. Using this cell-free system, we documented that Lys-29 of ubiquitin is the major site for ubiquitin chain formation to mediate DELLA protein degradation. We also confirmed the specific roles of GA receptors and multisubunit E3 ligase components in regulating DELLA protein degradation. In addition, blocking DELLA degradation with a PP1/PP2A phosphatase inhibitor in our cell-free assay suggested that degradation of DELLA proteins required protein Ser/Thr dephosphorylation activity. Furthermore, our data revealed that the LZ domain of Arabidopsis DELLA proteins is essential for both their stability and activity. Thus, our in vitro degradation system provides biochemical insights into the regulation of DELLA protein degradation. This in vitro assay system could be widely adapted for dissecting cellular signaling pathways in which regulated proteolysis is a key recurrent theme.
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DOI:10.1016/j.devcel.2019.05.018URLPMID:31178399 [本文引用: 1]
Plants exhibit different flowering behaviors in response to variable photoperiods across a wide geographical range. Here, we identify MYC3, a bHLH transcription factor, and its cis-element form the long-sought regulatory module responsible for cis-regulatory changes at the florigen gene FLOWERING LOCUS T (FT) that mediate natural variation in photoperiodic flowering responses in Arabidopsis. MYC3 is stabilized by DELLAs in the gibberellin pathway to suppress FT through binding the ACGGAT motif and antagonizing CONSTANS (CO) activation. Changing photoperiods modulate the relative abundance of MYC3 and CO, thus determining either of them as the predominant regulator for FT expression under different day lengths. Cis-regulatory changes in the MYC3 binding site at FT are associated with natural variation in day-length requirement for flowering in Arabidopsis accessions. Our findings reveal that environmental and developmental signals converge at MYC3 suppression of FT, an elementary event underlying natural variation in photoperiodic flowering responses.
DOI:10.1093/jxb/ers361URLPMID:23307919 [本文引用: 1]
Seed germination and flowering initiation are both transitions responding to similar seasonal cues. This study shows that ABSCISIC ACID-INSENSITIVE MUTANT 5 (ABI5), a bZIP transcription factor, which plays an important role in the abscisic acid (ABA)-arrested seed germination, is robustly associated with the floral transition in Arabidopsis. Under long-day conditions, overexpression of ABI5 could delay floral transition through upregulating FLOWERING LOCUS C (FLC) expression. In contrast, ectopically overexpressing FLC in an abi5 mutant reversed the earlier flowering phenotype. Further analysis indicated that transactivation of FLC could be promoted by ABI5 and/or other abscisic acid-responsive element (ABRE)-binding factors (ABFs). The expression of FLC that was promoted by ABI5 and/or other ABFs could be blocked in a triple SNF1-related protein kinase (SnRK) mutant, snrk2.2/2.3/2.6, despite the presence of ABA. In sharp contrast, when SnRK2.6 was coexpressed, the reduction of transactivity of FLC was reverted in mesophyll protoplasts of snrk2.2/2.3/2.6. Additional results from analysing transgenic plants carrying mutations of phosphoamino acids (ABI5 ( S42AS145AT201A )), which are conserved in ABI5, suggested that SnRK2-mediated ABI5 and/or ABF phosphorylation may be crucial for promoting FLC expression. The transgenic plants ABI5 ( S42AS145AT201A ) were insensitive to ABA in seed germination, in addition to having an earlier flowering phenotype. Direct binding of ABI5 to the ABRE/G-box promoter elements existing in FLC was demonstrated by chromatin immunoprecipitation. Mutations at the ABRE/G-box regions in FLC promoter sequences abolished the ABI5-promoted transactivation of FLC. In summary, these results may decipher the inhibitory effect of ABA on floral transition in Arabidopsis.
DOI:10.1093/jxb/erv459URLPMID:26507894 [本文引用: 1]
During the life cycle of a plant, one of the major biological processes is the transition from the vegetative to the reproductive stage. In Arabidopsis, flowering time is precisely controlled by extensive environmental and internal cues. Gibberellins (GAs) promote flowering, while abscisic acid (ABA) is considered as a flowering suppressor. However, the detailed mechanism through which ABA inhibits the floral transition is poorly understood. Here, we report that ABSCISIC ACID-INSENSITIVE 4 (ABI4), a key component in the ABA signalling pathway, negatively regulates floral transition by directly promoting FLOWERING LOCUS C (FLC) transcription. The abi4 mutant showed the early flowering phenotype whereas ABI4-overexpressing (OE-ABI4) plants had delayed floral transition. Consistently, quantitative reverse transcription-PCR (qRT-PCR) assay revealed that the FLC transcription level was down-regulated in abi4, but up-regulated in OE-ABI4. The change in FT level was consistent with the pattern of FLC expression. Chromatin immunoprecipitation-qPCR (ChIP-qPCR), electrophoretic mobility shift assay (EMSA), and tobacco transient expression analysis showed that ABI4 promotes FLC expression by directly binding to its promoter. Genetic analysis demonstrated that OE-ABI4::flc-3 could not alter the flc-3 phenotype. OE-FLC::abi4 showed a markedly delayed flowering phenotype, which mimicked OE-FLC::WT, and suggested that ABI4 acts upstream of FLC in the same genetic pathway. Taken together, these findings suggest that ABA inhibits the floral transition by activating FLC transcription through ABI4.
DOI:10.1146/annurev.genet.32.1.227URL [本文引用: 1]
DOI:10.1007/s10535-014-0401-1URL [本文引用: 1]
Interactions between indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene (ET) in the photoperiodic flower induction of a short-day (SD) plant Pharbitis nil were investigated. It was shown that both IAA and ABA applied just before and during the first half of the 16-h-long inductive night inhibited flower induction in P. nil. Ethylene is also thought to be a strong flowering inhibitor of SD plants but only when it is applied in the second half of the inductive night. The application of IAA just before the inductive night decreased the content of endogenous ABA in cotyledons only during the first half of the inductive night. Additionally, the application of 2-aminoethoxyvinylglycine (AVG) - an ethylene biosynthesis inhibitor - partially reversed the inhibitory effect of IAA and ABA on flowering. The results suggest that the mechanisms of P. nil flower inhibition by IAA and ABA might be independent. However, both the hormones influenced ethylene production which directly inhibited flowering. We also show that ABA applied on the cotyledons of P. nil seedlings just before the inductive night caused a clear increase in the expression of PnACS1 and PnACS2 genes (encoding enzymes involved in ethylene biosynthesis) from the first hours after its application. The transcripts of PnACO1 and PnACO3 genes were also increased but their maximal values were shifted in relation to the PnACS1 and PnACS2. The data presented here strongly support the idea that both IAA and ABA inhibit P. nil flowering through the modulation of ethylene biosynthesis.
DOI:10.1073/pnas.0610717104URLPMID:17389366 [本文引用: 1]
The length of the Arabidopsis thaliana life cycle depends on the timing of the floral transition. Here, we define the relationship between the plant stress hormone ethylene and the timing of floral initiation. Ethylene signaling is activated by diverse environmental stresses, but it was not previously clear how ethylene regulates flowering. First, we show that ethylene delays flowering in Arabidopsis, and that this delay is partly rescued by loss-of-function mutations in genes encoding the DELLAs, a family of nuclear gibberellin (GA)-regulated growth-repressing proteins. This finding suggests that ethylene may act in part by modulating DELLA activity. We also show that activated ethylene signaling reduces bioactive GA levels, thus enhancing the accumulation of DELLAs. Next, we show that ethylene acts on DELLAs via the CTR1-dependent ethylene response pathway, most likely downstream of the transcriptional regulator EIN3. Ethylene-enhanced DELLA accumulation in turn delays flowering via repression of the floral meristem-identity genes LEAFY (LFY) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Our findings establish a link between the CTR1/EIN3-dependent ethylene and GA-DELLA signaling pathways that enables adaptively significant regulation of plant life cycle progression in response to environmental adversity.
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DOI:10.1105/tpc.104.028514URLPMID:15749761 [本文引用: 1]
Histone acetylation is modulated through the action of histone acetyltransferases and deacetylases, which play key roles in the regulation of eukaryotic gene expression. Previously, we have identified a yeast histone deacetylase REDUCED POTASSIUM DEPENDENCY3 (RPD3) homolog, HISTONE DEACETYLASE19 (HDA19) (AtRPD3A), in Arabidopsis thaliana. Here, we report further study of the expression and function of HDA19. Analysis of Arabidopsis plants containing the HDA19:beta-glucuronidase fusion gene revealed that HDA19 was expressed throughout the life of the plant and in most plant organs examined. In addition, the expression of HDA19 was induced by wounding, the pathogen Alternaria brassicicola, and the plant hormones jasmonic acid and ethylene. Using green fluorescent protein fusion, we demonstrated that HDA19 accumulated in the nuclei of Arabidopsis cells. Overexpression of HDA19 in 35S:HDA19 plants decreased histone acetylation levels, whereas downregulation of HDA19 in HDA19-RNA interference (RNAi) plants increased histone acetylation levels. In comparison with wild-type plants, 35S:HDA19 transgenic plants had increased expression of ETHYLENE RESPONSE FACTOR1 and were more resistant to the pathogen A. brassicicola. The expression of jasmonic acid and ethylene regulated PATHOGENESIS-RELATED genes, Basic Chitinase and beta-1,3-Glucanase, was upregulated in 35S:HDA19 plants but downregulated in HDA19-RNAi plants. Our studies provide evidence that HDA19 may regulate gene expression involved in jasmonic acid and ethylene signaling of pathogen response in Arabidopsis.
DOI:10.1111/j.1744-7909.2011.01050.xURL [本文引用: 1]
Floral initiation is a major step in the life cycle of plants, which is influenced by photoperiod, temperature, and phytohormones, such as gibberellins (GAs). It is known that GAs promote floral initiation under short-day light conditions (SDs) by regulating the floral meristem-identity gene LEAFY (LFY) and the flowering-time gene SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1). We have defined the role of the auxin signaling component INDOLE-3-ACETIC ACID 7 (IAA7)/AUXIN RESISTANT 2 (AXR2) in the regulation of flowering time in Arabidopsis thaliana. We demonstrate that the gain-of-function mutant of IAA7/AXR2, axr2-1, flowers late under SDs. The exogenous application of GAs rescued the late flowering phenotype of axr2-1 plants. The expression of the GA20 oxidase (GA20ox) genes, GA20ox1 and GA20ox2, was reduced in axr2-1 plants, and the levels of both LFY and SOC1 transcripts were reduced in axr2-1 mutants under SDs. Furthermore, the overexpression of SOC1 or LFY in axr2-1 mutants rescued the late flowering phenotype under SDs. Our results suggest that IAA7/AXR2 might act to inhibit the timing of floral transition under SDs, at least in part, by negatively regulating the expressions of the GA20ox1 and GA20ox2 genes.
DOI:10.1007/s002999900177URL [本文引用: 1]
Jacq.) currently hampers the scaling-up of clonal plant production. In order to investigate the relationship between the “mantled” somaclonal variant and possible alterations in genomic DNA methylation rate, two complementary approaches have been used. HPLC quantification of relative amounts of 5-methyl-deoxycytidine has shown that global methylation in leaf DNA of abnormal regenerants is 0.5–2.5% lower than in their normal counterparts (20.8% vs 22%, respectively). When comparing nodular compact calli and fast growing calli, yielding respectively 5% and 100% of “mantled” plantlets, this decrease was up to 4.5% (from 23.2 to 18.7%). An alternative method, the SssI-methylase accepting assay, based on the enzymatic saturation of CG sites with methyl groups, gave convergent results. This work demonstrates that a correlation exists between DNA hypomethylation and the “mantled” somaclonal variation in oil palm.
DOI:10.1111/j.1744-7909.2006.00412.xURL [本文引用: 1]
Auxin has long been implicated in many aspects of plant growth and development including flower development. However, the exact roles of auxin in flower development have not been well defined until the recent identification of auxin biosynthesis mutants. Auxin is necessary for the initiation of floral primordia, and the disruption of auxin biosynthesis, polar auxin transport or auxin signaling leads to the failure of flower formation. Auxin also plays an essential role in specifying the number and identity of floral organs. Further analysis of the relationship between the auxin pathways and the known flower development genes will provide critical information regarding mechanisms of organogenesis and pattern formation in plants.
Author for correspondence. Tel: +1 858 822 2670; Fax: +1 858 534 7108; E-mail: yzhao@biomail.ucsd.edu
DOI:10.1105/tpc.12.4.507URLPMID:10760240 [本文引用: 1]
Leaves originate from the shoot apical meristem, a small mound of undifferentiated tissue at the tip of the stem. Leaf formation begins with the selection of a group of founder cells in the so-called peripheral zone at the flank of the meristem, followed by the initiation of local growth and finally morphogenesis of the resulting bulge into a differentiated leaf. Whereas the mechanisms controlling the switch between meristem propagation and leaf initiation are being identified by genetic and molecular analyses, the radial positioning of leaves, known as phyllotaxis, remains poorly understood. Hormones, especially auxin and gibberellin, are known to influence phyllotaxis, but their specific role in the determination of organ position is not clear. We show that inhibition of polar auxin transport blocks leaf formation at the vegetative tomato meristem, resulting in pinlike naked stems with an intact meristem at the tip. Microapplication of the natural auxin indole-3-acetic acid (IAA) to the apex of such pins restores leaf formation. Similarly, exogenous IAA induces flower formation on Arabidopsis pin-formed1-1 inflorescence apices, which are blocked in flower formation because of a mutation in a putative auxin transport protein. Our results show that auxin is required for and sufficient to induce organogenesis both in the vegetative tomato meristem and in the Arabidopsis inflorescence meristem. In this study, organogenesis always strictly coincided with the site of IAA application in the radial dimension, whereas in the apical-basal dimension, organ formation always occurred at a fixed distance from the summit of the meristem. We propose that auxin determines the radial position and the size of lateral organs but not the apical-basal position or the identity of the induced structures.
DOI:10.1007/BF00208313URLPMID:8904808 [本文引用: 1]
In the embryo of Arabidopsis thaliana (L.) Heynh., formation of the hypocotyl/root axis is initiated at the early-globular stage, recognizable as oriented expansion of formerly isodiametric cells. The process depends on the activity of the gene MONOPTEROS (MP); mp mutant embryos fail to produce hypocotyl and radicle. We have analyzed the morphology and anatomy of mp mutant plants throughout the Arabidopsis life cycle. Mutants form largely normal rosettes and root systems, but inflorescences either fail to form lateral flowers or these flowers are greatly reduced. Furthermore, the auxin transport capacity of inflorescence axes is impaired and the vascular strands in all analyzed organs are distorted. These features of the mutant phenotype suggest that the MP gene promotes cell axialization and cell file formation at multiple stages of plant development.
DOI:10.1007/s11103-011-9844-3URL [本文引用: 1]
During flower development, pluripotent stem cells within the floral meristem give rise to proliferative precursor cells whose progeny eventually acquire specialized functions within each floral organ. The regulatory mechanisms by which plant cells transition from a proliferating state to a differentiated state are not well characterized. Several members of the AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family, including AINTEGUMENTA (ANT) and AIL6/PLT3, are important regulators of cell proliferation in flowers. To further investigate the role of AIL6 during flower development, we have characterized transgenic plants in which the coding region of AIL6 was expressed under the control of the constitutive 35S promoter (35S:cAIL6). These plants display changes in floral organ size and morphology that are associated with alterations in the pattern and duration of cell divisions within developing organs. In addition, we find that very high levels of AIL6 expression inhibit cellular differentiation. In contrast, ant ail6 double mutants display premature differentiation of floral meristem cells. These results indicate that these two transcription factors regulate both proliferation and differentiation in flowers.
DOI:10.1104/pp.010587URLPMID:12481080 [本文引用: 1]
The auxin indole-3-acetic acid (IAA) has been shown to promote the biosynthesis of the active gibberellin (GA(1)) in shoots of pea (Pisum sativum). We used northern analysis to investigate the timing of IAA-induced changes in transcript levels of PsGA3ox1 (Mendel's LE), PsGA2ox1, PsGA2ox2, and PsGA20ox1, key genes for the later stages of GA(1) biosynthesis and metabolism in pea. Rapid (2-4 h) changes occurred in the transcript levels of PsGA3ox1, PsGA2ox1, and PsGA2ox2 after treatment with IAA. [(14)C]GA(1) metabolism studies in decapitated shoots indicated that IAA inhibits GA(1) deactivation, consistent with the suppression of PsGA2ox1 (SLN) transcript levels by IAA. Studies with the sln mutant also indicated that PsGA2ox1 activity is involved in GA(1) deactivation in decapitated shoots. Culture of excised internode tissue in the presence of auxin clearly demonstrated that internode tissue is a site of GA(1) biosynthesis per se. Excised internode tissue cultured in the presence/absence of cycloheximide showed that de novo protein synthesis is required for IAA-induced increases in PsGA3ox1 transcript levels. Auxin dose response studies indicated that IAA concentration is a critical determinant of GA(1) biosynthesis over 1 to 2 orders of magnitude, and a range of auxins was shown to affect the GA pathway.
DOI:10.1104/pp.106.084871URLPMID:16905669 [本文引用: 1]
Auxin and gibberellins (GAs) overlap in the regulation of multiple aspects of plant development, such as root growth and organ expansion. This coincidence raises questions about whether these two hormones interact to regulate common targets and what type of interaction occurs in each case. Auxins induce GA biosynthesis in a range of plant species. We have undertaken a detailed analysis of the auxin regulation of expression of Arabidopsis (Arabidopsis thaliana) genes encoding GA 20-oxidases and GA 3-oxidases involved in GA biosynthesis, and GA 2-oxidases involved in GA inactivation. Our results show that auxin differentially up-regulates the expression of various genes involved in GA metabolism, in particular several AtGA20ox and AtGA2ox genes. Up-regulation occurred very quickly after auxin application; the response was mimicked by incubations with the protein synthesis inhibitor cycloheximide and was blocked by treatments with the proteasome inhibitor MG132. The effects of auxin treatment reflect endogenous regulation because equivalent changes in gene expression were observed in the auxin overproducer mutant yucca. The results suggest direct regulation of the expression of GA metabolism genes by Aux/IAA and ARF proteins. The physiological relevance of this regulation is supported by the observation that the phenotype of certain gain-of-function Aux/IAA alleles could be alleviated by GA application, which suggests that changes in GA metabolism mediate part of auxin action during development.
DOI:10.1038/nature01387URLPMID:12610625 [本文引用: 1]
The growth of plant organs is influenced by a stream of the phytohormone auxin that flows from the shoot apex to the tip of the root. However, until now it has not been known how auxin regulates the cell proliferation and enlargement that characterizes organ growth. Here we show that auxin controls the growth of roots by modulating cellular responses to the phytohormone gibberellin (GA). GA promotes the growth of plants by opposing the effects of nuclear DELLA protein growth repressors, one of which is Arabidopsis RGA (for repressor of gal-3). GA opposes the action of several DELLA proteins by destabilizing them, reducing both the concentration of detectable DELLA proteins and their growth-restraining effects. We also show that auxin is necessary for GA-mediated control of root growth, and that attenuation of auxin transport or signalling delays the GA-induced disappearance of RGA from root cell nuclei. Our observations indicate that the shoot apex exerts long-distance control on the growth of plant organs through the effect of auxin on GA-mediated DELLA protein destabilization.
DOI:10.1016/j.pbi.2009.09.018URLPMID:19850510 [本文引用: 1]
Cytokinins are a class of phytohormones that regulate a wide variety of physiological and developmental processes such as shoot and root growth. Cytokinin signaling relies on a phosphorelay mechanism similar to the prokaryotic two-component system. Although the principal components mediating this cascade have been identified, only recently have we begun to understand the molecular basis of cytokinin action. For example cytokinins control cell differentiation rate during root meristem development by suppressing both auxin signaling and transport, whereas at early stages of embryo development auxin counteracts cytokinin signaling to establish the embryonic root stem-cell niche. The antagonistic interaction between cytokinins and auxin seems to also occur in other developmental processes, such as lateral root emergence and leaf initiation.
DOI:10.1093/aob/mcg053URLPMID:12646501 [本文引用: 1]
Eight-week-old vegetative plants of Arabidopsis thaliana, ecotype Columbia, were induced to flower by a single long day (LD). In this experimental system, it is known that the last component of the floral stimulus moves from the leaves to the apex 24-36 h after the start of the LD, and the first floral meristem is initiated by the shoot apical meristem (SAM) at 44-56 h (Corbesier et al., 1996, The Plant Journal 9: 947-952). Here we show that the rate of cell division is increased at floral transition in all SAM parts but not in the sub-apical pith cells. Mitotic activity starts to increase 24 h after the start of the LD and is two- to three-fold higher at peak times than that in non-induced plants. This activation is followed by the start of SAM enlargement at 44 h, SAM doming at 48 h, and the elongation of apical internodes (bolting) at 52 h.
DOI:10.1105/tpc.110.079079URL [本文引用: 1]
The size and activity of the shoot apical meristem is regulated by transcription factors and low molecular mass signals, including the plant hormone cytokinin. The cytokinin status of the meristem depends on different factors, including metabolic degradation of the hormone, which is catalyzed by cytokinin oxidase/dehydrogenase (CKX) enzymes. Here, we show that CKX3 and CKX5 regulate the activity of the reproductive meristems of Arabidopsis thaliana. CKX3 is expressed in the central WUSCHEL (WUS) domain, while CKX5 shows a broader meristematic expression. ckx3 ckx5 double mutants form larger inflorescence and floral meristems. An increased size of the WUS domain and enhanced primordia formation indicate a dual function for cytokinin in defining the stem cell niche and delaying cellular differentiation. Consistent with this, mutation of a negative regulator gene of cytokinin signaling, ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN 6, which is expressed at the meristem flanks, caused a further delay of differentiation. Terminal cellular differentiation was also retarded in ckx3 ckx5 flowers, which formed more cells and became larger, corroborating the role of cytokinin in regulating flower organ size. Furthermore, higher activity of the ckx3 ckx5 placenta tissue established supernumerary ovules leading to an increased seed set per silique. Together, the results underpin the important role of cytokinin in reproductive development. The increased cytokinin content caused an similar to 55% increase in seed yield, highlighting the relevance of sink strength as a yield factor.
DOI:10.1093/jxb/erg276URLPMID:14512385 [本文引用: 1]
Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis thaliana has been successfully used to unravel signalling pathways by genetic and molecular approaches, but analyses are still required to determine the physiological signals involved in the control of floral transition. In this work, the putative role of cytokinins was investigated using vegetative plants of Arabidopsis (Columbia) induced to flower synchronously by a single 22 h long day. Cytokinins were analysed in leaf extracts, leaf phloem exudate and in the shoot apical meristem at different times during floral transition. It was found that, in both the leaf tissues and leaf exudate, isopentenyladenine forms of cytokinins increased from 16 h after the start of the long day. At 30 h, the shoot apical meristem of induced plants contained more isopentenyladenine and zeatin than vegetative controls. These cytokinin increases correlate well with the early events of floral transition.
DOI:10.1023/A:1016343421814URL [本文引用: 1]
DOI:10.1111/j.1399-3054.2010.01430.xURLPMID:21077902 [本文引用: 1]
The ability to control the timing of flowering is a key strategy in planning the production of ornamental species such as azaleas; however, it requires a thorough understanding of floral transition. DNA methylation is involved in controlling the functional state of chromatin and gene expression during floral induction pathways in response to environmental and developmental signals. Plant hormone signalling is also known to regulate suites of morphogenic processes in plants and its role in flowering-time control is starting to emerge as a key controlling step. This work investigates if the gibberellin (GA) inhibitors and chemical pinching applied in improvement of azalea flowering alter the dynamics of DNA methylation or the levels of polyamines (PAs), GAs and cytokinins (CKs) during floral transition, and whether these changes could be related to the effects observed on flowering ability. DNA methylation during floral transition and endogenous content of PAs, GAs and CKs were analysed after the application of GA synthesis inhibitors (daminozide, paclobutrazol and chlormequat chloride) and a chemical pruner (fatty acids). The application of GA biosynthesis inhibitors caused alterations in levels of PAs, GAs and CKs and in global DNA methylation levels during floral transition; also, these changes in plant growth regulators and DNA methylation were correlated with flower development. DNA methylation, PA, GA and CK levels can be used as predictive markers of plant floral capacity in azalea.
[本文引用: 1]
DOI:10.1104/pp.54.6.904URLPMID:16658997 [本文引用: 1]
Honeydew produced by the aphid Dactynotus ambrosiae when feeding on flowering or vegetative plants of the short day plant Xanthium strumarium contains an active substance capable of inducing flowering in the long day plant Lemna gibba G3. In the present study, this active material has been identified as salicylic acid through the use of gas-liquid chromatography and mass, infrared, and ultraviolet spectrometry. Authentic salicylic acid induces flowering in L. gibba G3 under strict short day conditions with an optimal response at about 5.6 mum. The possible significance of salicylic acid for the control of flowering in Xanthium or L. gibba G3 is discussed.
DOI:10.1104/pp.100.3.1541URLPMID:16653155 [本文引用: 3]
Lemna paucicostata LP6 does not normally flower when grown on basal Bonner-Devirian medium, but substantial flowering is obtained when 10 mum salicylic acid (SA) or benzoic acid is added to the medium. Benzoic acid is somewhat more effective than SA, and the threshold level of both SA and benzoic acid required for flower initiation is reduced as the pH of the medium is lowered to 4.0. SA- or benzoic acid-induced flowering is enhanced in the simultaneous presence of 6-benzylaminopurine (BAP), although BAP per se does not influence flowering in strain LP6. Continuous presence of SA or benzoic acid in the culture medium is essential to obtain maximal flowering. A short-term treatment of the plants (for first 24 h) with 10 mum SA or benzoic acid, followed by culture in the basal medium containing 1 mum BAP can, however, stimulate profuse flowering. Benzoic acid is more effective than SA, and the effect is more pronounced at pH 4 than at 5.5. Thus, under these conditions, flowering is of an inductive nature. Experiments with [(14)C]SA and [(14)C]benzoic acid have provided evidence that at pH 4 there is relatively more uptake of benzoic acid than SA, thus leading to an increased flowering response. The data obtained from the experiments designed to study the mobility of [(14)C]SA and [(14)C]-benzoic acid from mother to daughter fronds indicate that there is virtually no mobility of SA or benzoic acid between fronds.
DOI:10.1016/j.jplph.2009.10.006URLPMID:19906461 [本文引用: 2]
The short-day plants Pharbitis nil (synonym Ipomoea nil), var. Violet and Tendan were grown in a diluted nutrient solution or tap water for 20 days under long-day conditions. Violet plants were induced to flower and vegetative growth was inhibited, whereas Tendan plants were not induced to flower, although vegetative growth was inhibited under these conditions. The Violet plants induced to flower by poor-nutrition stress produced fertile seeds and their progeny developed normally. Defoliated Violet scions grafted onto the rootstocks of Violet or Tendan were induced to flower under poor-nutrition stress conditions, but Tendan scions grafted onto the Violet rootstocks were not induced to flower. These results indicate that a transmissible flowering stimulus is involved in the induction of flowering by poor-nutrition stress. The poor-nutrition stress-induced flowering was inhibited by aminooxyacetic acid, a phenylalanine ammonia-lyase inhibitor, and this inhibition was almost completely reversed by salicylic acid (SA). However, exogenously applied SA did not induce flowering under non-stress conditions, suggesting that SA may be necessary but not sufficient to induce flowering. PnFT2, a P. nil ortholog of the flowering gene FLOWERING LOCUS T (FT) of Arabidopsis thaliana, was expressed when the Violet plants were induced to flower by growing in tap water, but expression of PnFT1, another ortholog of FT, was not induced, suggesting the specific involvement of PnFT2 in stress-induced flowering.
DOI:10.4161/psb.5.8.11826URLPMID:20505356 [本文引用: 1]
Many plant species can be induced to flower by responding to stress factors. The short-day plants Pharbitis nil and Perilla frutescens var. crispa flower under long days in response to the stress of poor nutrition or low-intensity light. Grafting experiments using two varieties of P. nil revealed that a transmissible flowering stimulus is involved in stress-induced flowering. The P. nil and P. frutescens plants that were induced to flower by stress reached anthesis, fruited and produced seeds. These seeds germinated, and the progeny of the stressed plants developed normally. Phenylalanine ammonia-lyase inhibitors inhibited this stress-induced flowering, and the inhibition was overcome by salicylic acid (SA), suggesting that there is an involvement of SA in stress-induced flowering. PnFT2, a P. nil ortholog of the flowering gene FLOWERING LOCUS T (FT) of Arabidopsis thaliana, was expressed when the P. nil plants were induced to flower under poor-nutrition stress conditions, but expression of PnFT1, another ortholog of FT, was not induced, suggesting that PnFT2 is involved in stress-induced flowering.
DOI:10.1046/j.1365-313x.2003.01954.xURLPMID:14690505 [本文引用: 1]
Flowering relies on signaling networks that integrate endogenous and external cues. Normally, plants flower at a particular season, reflecting day length and/or temperature cues. However, plants can surpass this seasonal regulation and show precocious flowering under stress environmental conditions. Here, we show that UV-C light stress activates the transition to flowering in Arabidopsis thaliana through salicylic acid (SA). Moreover, SA also regulates flowering time in non-stressed plants, as SA-deficient plants are late flowering. The regulation of flowering time by SA seems to involve the photoperiod and autonomous pathways, but it does not require the function of the flowering time genes CONSTANS (CO), FCA, or FLOWERING LOCUS C (FLC).
