,, 孙亮, 谭龙涛中国科学院亚热带农业生态研究所,长沙 410125Progress in ZIP transporter gene family in rice
Lu Meng,, Liang Sun, Longtao TanInstitute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China第一联系人:
收稿日期:2017-07-19修回日期:2017-11-19网络出版日期:--
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Received:2017-07-19Revised:2017-11-19Online:--
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孟璐, 孙亮, 谭龙涛. 水稻锌铁转运蛋白ZIP基因家族研究进展. 遗传[J], 2018, 40(1): 33-43 doi:10.16288/j.yczz.17-238
Lu Meng, Liang Sun, Longtao Tan.
锌(Zn)和铁(Fe)作为水稻生长必需的矿物元素,在其生长发育过程中发挥着重要作用。Zn是300多种酶和重要蛋白质的结构辅助因子,在生物体代谢、生物膜稳定和基因的表达调控等生理机能中发挥重要的作用。Fe在植物细胞呼吸、光合作用和金属蛋白的催化反应过程中起着重要作用[1,2,3]。水稻(Oryza sativa L.)体内Zn、Fe含量的适当增加可提高作物产量和品质,而缺乏将对水稻的生长发育造成严重影响,导致产量和品质下降,其中主要表现为植株矮小和水稻籽粒中Zn、Fe含量不足[4,5,6]。
Zn和Fe也是人体必需的微量元素,其在体内的累积与人体健康密切相关。水稻是世界上多数人口的主食,但稻米中Zn和Fe的含量相对较低,容易导致人体营养不良。通过生物强化措施,提高水稻中Zn、Fe含量能够安全、有效地解决Zn、Fe营养缺乏问题[7]。因此,研究水稻体内Zn和Fe等微量元素转运的相关蛋白,了解各种转运蛋白家族成员在吸收、转运和分配金属元素中的作用,对提高水稻产量和稻米品质具有重要意义。
各种转运蛋白在植物体内主要通过协同作用来吸收、转运和分配金属元素,控制植物体内金属离子的平衡,这些转运蛋白包括阳离子扩散协助蛋白(cation diffusion facility protein, CDF)、重金属ATP酶(heavy metal ATPases of the P1B-type ATPase, HMA)、自然抵抗相关巨噬细胞蛋白(natural resistance associated macrophage proteins, NRAMP)、锌铁调控转运相关蛋白(zinc-regulated transporters, iron-regulated transporter-like protein, ZIP)等[8,9,10,11,12,13,14]。其中,CDF主要负责将Zn从胞内转移到胞外[10,11,13];HMA主要是通过ATP水解释放的能量进行转运金属离子[10,11];NRAMP主要参与二价金属阳离子的转运[10,14];ZIP主要参与金属离子的吸收、转运和分配过程。ZIP转运蛋白不仅能转运Zn和Fe等必需的营养元素,还能转运Cd、Pb、Ni等有害重金属元素[10,15~17]。因此,本文概述了ZIP转运蛋白在水稻体内的亚细胞定位、表达模式、转运机制和调节金属离子互作,以及在自然群体中的等位变异等,为研究水稻稻米微量元素的积累提供理论基础。
1 ZIP基因家族的结构特征和分布
ZIP转运蛋白包括锌调控转运蛋白(zinc-regulated transporter, ZRT)和铁调控转运蛋白(iron-regulated transporter, IRT)[18]。目前已知水稻ZIP基因家族包含16个成员,其中14个为锌调控转运蛋白基因,2个为铁调控转运蛋白基因[19,20]。ZIP基因家族成员在水稻1~8号染色体上均有分布(图1),而且在5号染色体上有OsZIP5、OsZIP6、OsZIP7、OsZIP9和OsZIP11基因,是拥有ZIP基因最多的一条染色体,其中OsZIP5和OsZIP9两个基因串联,位置临近[19];OsIRT1和OsIRT2在3号染色体上串联分布[21,22],序列相似度为86%。这说明ZIP基因分布可能不是随机的。另外,利用水稻ZIP家族16个基因的mRNA序列进行系统进化分析(MEGA7.0.14),直观揭示了ZIP基因之间的亲缘关系(图2)。ZIP转运蛋白一般由326~425个氨基酸残基组成[15],对水稻ZIP家族成员的氨基酸序列分析发现,多数ZIP转运蛋白含有8个跨膜结构域(图3),而且在第Ⅲ第Ⅳ跨膜区之间有一个位于胞内的富含组氨酸残基的可变区,该区可能与金属离子的结合、转运有关[15,19,23]。另外,金属离子和转运蛋白结合可形成八面体、四面体和平面等多种结构[24]。
图1
新窗口打开|下载原图ZIP|生成PPT图1水稻部分ZIP基因分布图
OsIRT1：LOC_Os03g46470.1;OsIRT2：LOC_Os03g46454.1;OsZIP1：LOC_Os01g74110.1;OsZIP2：LOC_Os03g29850.1;OsZIP3：LOC_Os04g52310.1;OsZIP4：LOC_Os08g10630.1;OsZIP5：LOC_Os05g39560.1;OsZIP6：LOC_Os05g07210.1;OsZIP7：LOC_Os05g10940.1;OsZIP8：LOC_Os07g12890.1;OsZIP9：LOC_Os05g39540.1;OsZIP10：LOC_Os06g37010.1;OsZIP11：LOC_Os05g25194.1;OsZIP13：LOC_Os02g10230.1;OsZIP14：LOC_Os08g36420.5 ;OsZIP16：LOC_Os08g01030.1。
Fig. 1The genetic map of ZIP genes in rice
图2
新窗口打开|下载原图ZIP|生成PPT图2水稻ZIP基因家族系统进化树
Fig. 2A phylogenetic tree of ZIP genes in rice
图3
新窗口打开|下载原图ZIP|生成PPT图3水稻ZIP转运蛋白氨基酸序列比对结果
Fig. 3Amino acid alignment of the predicted ZIP transporters in rice
2 ZIP基因家族生物学功能
对水稻ZIP家族大部分基因已进行了初步研 究(表1)。利用酵母营养缺陷型突变体互补实验证 明OsIRT1、OsIRT2、OsZIP1、OsZIP3、OsZIP4、OsZIP5和OsZIP8等家族成员均有转运Zn、Fe的功能[19,21,25~29]。研究发现,OsZIP10可能定位于叶绿体,其他ZIP转运蛋白主要定位于细胞膜[19,22],说明ZIP转运蛋白是金属离子跨膜转运的重要转运蛋白。Table 1
表1
表1 水稻ZIP基因家族部分成员及可能的功能
Table 1
| OsZIPs | 表达部位 | 诱导条件 | 可能功能 | 参考文献 |
|---|---|---|---|---|
| OsZIP1 | 根和花穗 | 缺Zn | 吸收和转运Zn,转运Cd | [19,26] |
| OsZIP2 | 根 | 缺Zn | 吸收Fe | [26] |
| OsZIP3 | 各组织和茎节 | 无 | Zn分配 | [19,28] |
| OsZIP4 | 地上部和根 | 缺Zn | 转运Zn | [25,30] |
| OsZIP5 | 根 | 缺Zn、Mn | 吸收Zn | [31] |
| OsZIP6 | 地上部和根部 | 缺Zn、Fe、Mn | 吸收Zn及向地上部转运 | [24] |
| OsZIP7 | 地上部和根 | 缺Zn | - | [25] |
| OsZIP8 | 根和地上部 | 缺Fe | 吸收和分配Zn | [29] |
| OsIRT1 | 根和茎的韧皮部 | 缺Fe | 吸收和转运Fe、Zn、Cd | [21,32~34] |
| OsIRT2 | 根 | 缺Fe | 吸收Fe,吸收和转运Cd | [21,33,34] |
新窗口打开|下载CSV
2.1 铁调控转运体
ZIP家族两个转运蛋白基因IRT1和IRT2在水稻、拟南芥(Arabidopsis thaliana L.)、大麦(Hordeum vulgare L.)和大豆(Glycine max L.)等多种植物中研究的较为清楚。OsIRT1和OsIRT2在水稻ZIP家族中主要负责Fe的转运,缺Fe诱导条件下根部基因表达量升高[21]。另外,OsIRT1还能转运Zn和Cd[32,33]。OsIRT1过表达材料不仅提高了OsIRT1的表达水平,还能提高苗期对缺铁胁迫的抗性和对过量Zn、Cd的敏感性。在大田条件下,过表达OsIRT1水稻在苗期并未出现表型差异,但从生殖期开始出现明显的表型差异,表现为植株矮小、分蘖减少、产量降低,但籽粒中Fe和Zn的含量升高[34]。由此可见,OsIRT1能够提高水稻籽粒中Fe、Zn的积累,但造成水稻 减产。OsIRT2也能转运Cd,但是转运能力远小于OsIRT1[33]。另外,拟南芥和大麦中的IRT1同样表现出转运多种金属离子如Mn2+、Fe2+、Zn2+和Cd2+的能力,但只在缺Mn和缺Fe诱导条件下上调表达[35,36,37]。Connolly等[38]研究也发现,在缺Fe的营养液中培养6天后拟南芥根部Cd含量增加,地上部含量减少,而且过表达AtIRT1后拟南芥对Cd更敏感。这些结果说明,AtIRT1不但能维持拟南芥体内Fe的代谢平衡,而且可能参与了重金属Cd的转运。另外,Ni胁迫也能引起AtIRT1表达升高,可能原因是Ni与Fe具有竞争关系,Ni胁迫引起缺铁响应,从而造成IRT1表达升高[17]。HvIRT1是大麦中负责根吸收Mn的重要转运蛋白之一,Mn缺乏诱导后,不同HvIRT1基因型(Vanessa和Antonia)大麦对Mn吸收效率差异显著,在Mn高效基因型(Vanessa)大麦中表达量上调40%[35]。总之,IRT1和IRT2在植物中具有不同的转运底物,尤其是Fe、Zn、Mn 3种元素,因此IRT1和IRT2可能参与对多种金属元素的吸收、转运过程,是金属转运过程中的重要蛋白。2.2 锌调控转运体
OsZIP1、OsZIP2、OsZIP4、OsZIP5、OsZIP6、OsZIP7和OsZIP8都与Zn的运输有关[19,23,24,28]。Ramesh等[26]从水稻基因组中分离鉴定了OsZIP1、OsZIP2和OsZIP3的全长cDNA序列,并且在缺Zn诱导下根部OsZIP1表达量升高。通过酵母缺Zn突变体互补实验发现,OsZIP1在酵母内具有转运Zn的能力。也有研究发现,在缺Zn条件下,OsZIP1在根和花穗中诱导上调表达[19];OsZIP2只在根中上调表达[26]。Matthew等[39]研究拟南芥ZIP家族基因发现,AtZIP1主要在根和叶脉中表达,AtZIP2在根中柱表达量较高,这两个基因分别定位在液泡膜和质膜上;AtZIP1可能参与金属离子从液泡释放到根细胞质的再活化过程,而AtZIP2可能参与根对Mn和Zn的吸收;对缺失突变体的研究结果表明,AtZIP1、AtZIP2在Mn和Zn从根部向地上部的转运过程中发挥一定的作用。OsZIP3与Zn的分配有关,但OsZIP3不受缺Zn和高Zn诱导[28],这与苜蓿(Medicago truncatula L.)和大麦中的ZIP3显著不同：缺Zn诱导时,MtZIP3在根和叶片中上调表达[40],HvZIP3在根中上调表达[41]。虽然OsZIP3的表达没有变化,但是OsZIP3突变体与野生型相比Zn的含量有显著差异,突变体的地上部(不包括基部)Zn的含量升高,地上部基部区域Zn含量显著下降[28]。通过短期同位素标记法标记67Zn发现,OsZIP3主要在水稻节中表达,敲除OsZIP3后,Zn含量在下部叶较高,在地上部伸长区和节点含量较低,这表明OsZIP3的作用在于将Zn从节处分配到快速生长的组织内[28]。另外,通过抑制OsZIP3的表达并未影响根对Zn的吸收和Zn由根向地上部的转运,由此证明OsZIP3与其他植物中的ZIP3转运蛋白在功能上存在差异,OsZIP3只与Zn分配有关,不参与Zn的吸收和转运过程[28]。
OsZIP4与Zn的转运和再分配有关。OsZIP4主要在叶片的维管束和叶肉细胞、茎和根的韧皮部表达,另外根尖和茎的分生组织中表达较为明显。因此,OsZIP4的功能可能同时涉及Zn在水稻体内的转运与再分配过程[25]。Northern分析结果显示：缺Zn诱导时,OsZIP4在根中与叶片中的上调表达的时间不同步,地上部的诱导时间比根部长,而且添加Zn恢复正常生长后,OsZIP4表达量缓慢降低[25]。由此推测,OsZIP4可能参与了Zn的长距离运输。另外,缺Zn诱导时,水稻的老叶和新叶中的OsZIP4表达量也同时增加,但新叶的表达量较高,因此缺Zn诱导时,OsZIP4更倾向于在分生能力强的器官中表达[25]。但在苜蓿中ZIP4的表达与Fe、Zn、Mn 3种元素有关,这与水稻ZIP4的专一性有很大差别,缺Mn、缺Fe诱导时,叶片中MtZIP4下调表达;而缺Zn诱导时,根和叶片中MtZIP4上调表达[40]。
OsZIP5和OsZIP6能转运多种二价金属离子[24,31]。在水稻中,OsZIP5受Zn、Fe和Mn缺乏诱导上调表达。缺Zn诱导下,OsZIP5在根部和地上部表达量升高,缺Fe和Mn诱导时只在根中表达量升高[31]。OsZIP5突变体可增加对超Zn环境的耐受性并降低水稻中Zn含量;然而,过表达OsZIP5水稻对超Zn环境敏感[31]。在Zn、Fe和Mn缺乏诱导时,OsZIP6地上部表达水平升高3倍,但在地下部,只有缺Fe诱导时根中OsZIP6表达量才达到相同水平[24]。同样,在苜蓿中MtZIP5也受缺Zn或缺Mn的诱导,在缺Zn或缺Mn条件下,叶片中MtZIP5上调表达,但是MtZIP6的表达与金属元素含量无关[40]。
OsZIP8与OsZIP4具有相似的表达模式,缺Zn诱导时,根部和地上部的OsZIP8上调表达,在恢复正常生长过程中,OsZIP8和OsZIP4表达量都降低,但表达差异较大,OsZIP4表达量降低过程持续时间长,OsZIP8的表达是短时迅速降低,最终表达量稳定,但根中表达量远大于地上部的表达量[29]。OsZIP8负责Zn的吸收和分配,OsZIP8过表达后,株高降低,地上部Zn含量降低,根中Zn含量极显著升高;在超Zn胁迫下,造成转基因株系地上部Zn含量降低,在大田中出现表型差异,尤其是在花期,出现株高显著降低、分蘖减少、产量降低,而且旗叶中Zn含量降低,但其他金属含量无变化,这说明OsZIP8过表达干扰了水稻对Zn的分配使地上部和籽粒中Zn的含量降低,根中Zn含量增加[29]。另外,过表达OsZIP4和OsZIP5导致Zn大量聚集于根部,地上部和籽粒中Zn含量降低[30,31]。
目前研究表明,不同植物中的ZIP家族具有吸收、转运和分配Zn、Fe、Mn等多种元素的能力,但功能存在显著不同。相同物种,基因的相似性越高,转运蛋白越可能有相似的表达模式,如OsIRT1和OsIRT2。在研究转运蛋白功能时,一般情况下,同源基因具有类似的转运模式的可能性比较大,但在ZIP家族中,由于其他物种与水稻生存环境的差异或者其他因素,造成同源基因的功能存在差异,如OsZIP4只与Zn的分配和转运有关,但MtZIP4却与Zn、Fe、Mn 3种元素有关;OsZIP8受Zn诱导表达,过表达后会导致Zn在水稻体内再分配,但在拟南芥中,ZIP8转运蛋白对Zn、Fe、Mn、Cu可能都无转运活性[39],因此ZIP8转运蛋白在不同植物中的功能存在极大差异。
3 ZIP基因家族吸收、转运和分配机制
转运蛋白对微量元素的转运主要有4种模式：木质部转换模式(xylem-switch mode)、韧皮部专一性模式(phloem-tropic mode)、韧皮部反冲模式(phloem- kickback mode)和低浓度转换模式(minimum-shift mode)[42]。Xylem-switch模式主要是将微量元素从木质部的扩大维管束(enlarged vascular bundles, EVBs)转运到木质部的分散维管束(diffuse vascular bundles, DVBs);Phloem-tropic模式是指金属元素仅通过韧皮部转运;Phloem-kickback模式与其他模式最大的不同是将微量元素先分配到叶片,然后再通过木质部转运重新分配到发育组织中。Minimum-shift模式根据环境中浓度变化调控元素分配[42]。不同矿物元素通过不同模式利用不同的转运蛋白进行转运。Zn主要是通过Phloem-tropic模式转运[42]。由于发育的组织在细胞分裂和生长过程中需要大量的Zn,Zn从土壤中吸收后优先分配到新叶、节等器官中[43,44,45]。在水稻主茎上一般有13~18个茎节,但只有上边的4~5个节间不断伸长生长,在茎基部有10个左右的茎节聚集在一起[42,46]。茎节连接分蘖、茎和叶鞘,是水稻连接各组织器官的要塞,并将水稻的维管束系统连接在一起。水稻的维管束有3种不同类型：EVBs、DVBs和TVBs (transit vascular bundles, TVBs),这3种维管束可共同存在,承担不同的职责[46,47]。在营养生长和生殖生长期,茎节中Zn的含量比其他器官高[48,49,50],由此可见在该阶段大量Zn聚集于茎节处,此时茎节处的转运蛋白将Zn转运到叶鞘和分蘖,或者向上转运,从而促进水稻的生长。在茎节里,Zn储存在EVBs和DVBs的薄壁细胞[43~45,49,50]。OsZIP3是节中调控Zn分配的一个重要转运蛋白,但OsZIP3不能独自完成转运Zn的过程,至少需要重金属ATP酶2(heavy metal ATPase 2, HMA2)和另一个未知转运蛋白[28,51]。OsHMA2位于韧皮部的DVBs和EVBs上,主要转运Zn和Cd,在Zn分配过程中负责将Zn转运到韧皮部的DVBs和EVBs中。OsZIP3在茎节处分配Zn的具体的机制为：首先,从根部吸收的Zn储存在木质部薄壁细胞里,OsZIP3将位于木质部的EVBs中的Zn转运出来;然后,一个未知转运蛋白将锌转运到质外体的DVBs中;最后OsHMA2将Zn转运到韧皮部,使Zn向上运输;同时,OsHMA2可将木质部EVBs中的锌直接转运到韧皮部的EVBs,从而使Zn分配到叶片。在该机制中,敲除OsHMA2基因,导致水稻生长减弱,这是由于Zn的分配受到了影响,但是敲除OsZIP3,却没有明显的表型,水稻正常生长,并且也未影响OsHMA2的表达,说明在OsZIP3的转运机制中存在其他与OsZIP3功能类似的转运蛋白,当OsZIP3转运受阻时,其他转运蛋白会承担相应的功能[28]。4 ZIP基因家族参与多种金属离子的转运
OsIRT1和OsIRT2不仅转运Fe,也能转运Zn和Cd。OsIRT1和OsIRT2转运Cd的能力取决于环境中Fe的浓度,Fe充足时转运Cd的能力小于Fe缺乏时;若环境Cd的浓度足够高将影响Fe和Zn的吸收,造成植株内Fe和Zn含量降低。由此可见,Fe与Cd存在竞争关系[33]。OsIRT1对Cd的效应远大于OsIRT2,而且OsIRT1不仅能促进Cd的吸收还能转运和分配Cd[33]。除此之外,在拟南芥中IRT1能转运Ni,Ni与Fe也具有竞争关系[17]。OsZIP1也具有转运Cd的能力[26],OsZIP5表达受Zn、Mn两种元素诱导[31],OsZIP6表达受Fe、Zn和Mn 3种元素诱导,并且通过放射性同位素吸收发现,Co能影响OsZIP6转运蛋白对Fe的转运[24]。除此之外,ZIP基因在某种离子的诱导下会导致植物体其他金属元素含量的变化,如缺Zn诱导下,根中铁含量增加两倍,出现此种现象的原因并不是OsZIP4具有转运Fe的能力,而是OsZIP4的表达影响了其他铁转运蛋白的功能[25]。在烟草(Nicotiana tabacum L.)和大麦中也有类似现象,缺Zn诱导时会导致植物体内的Fe含量明显高于对照组[52,53]。另外,不同ZIP转运蛋白即使在相同诱导条件下基因的表达量也不一致,同样缺Zn诱导条件下,OsZIP4在根部和地上部的表达量同时增加两倍,但OsZIP6只在地上部表达,但表达量提高了3倍[24]。Zn和Cd都是通过Phloem-tropic模式转运,Mn通过Minimum-shift模式转运[42]。根据目前已知的ZIP基因功能,OsIRT1与Zn、Fe和Cd有关[21,32,33];OsZIP1与Zn和Cd有关[19,26];OsZIP5与Zn和Mn有关[31];OsZIP6与Zn、Fe和Mn有关[24]。由此可见,ZIP基因不是单独在某一种模式里转运金属离子,而是在不同模式中发挥作用。
5 ZIP基因具有丰富的等位变异
水稻种质资源丰富,拥有大量的地方品种和野生种质。通过长期的自然进化和人工选择,不同品种包含了大量的优良自然变异,这些有利变异是许多重要农艺性状的遗传基础。根据不同自然变异的分子特征,对一个品种的相关性状进行遗传构成分析,通过测序了解不同位点的自然变异类型,有目的的改良劣势位点,可为分子育种提供理论依据[54,55]。华中农业大学水稻基因组序列变异综合数据库RiceVarMap(http://ricevarmap.ncpgr.cn/)整合了来自全世界73个国家的1479份栽培稻的测序数据,鉴定了6 551 358个SNP位点和1 214 627个INDEL位点,并获得了这些变异位点在不同品种中的分布信息,可以容易了解不同品种的遗传构成,挖掘更多的自然变异[56]。利用此数据库初步分析ZIP家族基因编码区的自然变异,发现不同水稻品种间ZIP基因存在丰富的自然变异(图4)。OsZIP1存在3种基因型,其中有2种基因型分部较为广泛;OsZIP2存在5种主要基因型,其中有1种基因型分部较为广泛;OsZIP3存在5种主要基因型,其中有2种基因型分部较为广泛;OsZIP4存在8种主要基因型,其中有2种基因型分部较为广泛;OsZIP5存在5种主要基因型,其中有2种基因型分部较为广泛;OsZIP6存在3种主要基因型,其中只有1种基因型分部较为广泛;OsZIP7、OsZIP8和OsZIP9均有2种基因型分部较为广泛;OsZIP10、OsIRT1和 OsIRT2只有1种基因型分部较为广泛。值得一提的是,除OsZIP2、OsZIP6、OsIRT1和OsIRT2外,它们的某些单倍型只在籼稻或粳稻中出现,这说明ZIP家族基因存在明显的籼粳分化。因此,我们推测这些ZIP基因的籼、粳稻间的自然变异很可能造成了不同品种籼、粳稻中Zn和Fe积累的差异。图4
新窗口打开|下载原图ZIP|生成PPT图4ZIP基因自然变异的初步分析
圆饼代表不同单倍型,圆饼面积代表品种数量,品种数量>10;直线代表亲缘关系,蓝色代表籼稻,绿色代表粳稻,灰色代表中间型。
Fig. 4Preliminary analyses of the natural variation in OsZIPs
6 结语与展望
ZIP基因家族是维持水稻体内Zn、Fe平衡的重要转运蛋白家族之一。到目前为止,ZIP基因家族有10个成员的基因信息、表达定位和转运能力已较为清楚,它们都位于细胞膜上,序列相似性较大,含有8个跨膜结构域,而且在第Ⅲ和第Ⅳ可变区内存在与金属离子结合的位点。除OsZIP3之外,其他ZIP家族基因均可受缺Zn、缺Fe、缺Mn诱导表达上调。另外,ZIP家族成员主要对Zn、Fe亲和力较大,但也转运Cd、Co等,Cd、Co不具有专一的转运蛋白。不同金属离子处于动态平衡之中,互相影响,一种元素的变化会影响到一些转运蛋白的表达变化,最终导致金属离子含量变化。当某种金属离子含量超出水稻自身耐受能力时,植物生长会受到严重抑制甚至死亡。虽然已有大量研究表明ZIP家族蛋白参与了Zn、Fe 和Cd等元素的吸收、转运和分配,但它们是否影响到Zn、Fe 和Cd在稻米中的积累及其在自然群体中的变异规律还需要进一步研究。深入研究ZIP转运蛋白转运Zn、Fe的分子机制及其在籽粒中积累的规律,为人们培育富Zn或富Fe水稻提供理论基础;同时通过研究ZIP转运蛋白对Cd等有害金属元素的吸收和积累规律,降低根对Cd的吸收和籽粒中积累。虽然已有大量关于ZIP基因家族的研究,但除OsZIP3外,对其他成员的功能研究还不够深入。另外,对Zn、Fe在籽粒中的积累机制研究和自然群体中ZIP基因的等位变异研究也不够深入。因此,对ZIP转运蛋白家族的吸收、转运、分配以及对Zn、Fe在籽粒中的积累机制等方面仍存在较大的研究空间。
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[本文引用: 1]
URLPMID:27671163 [本文引用: 1]
Zinc (Zn) is one of the most essential micronutrients required for the growth and development of human beings. More than one billion people, particularly children and pregnant women suffer from Zn deficiency related health problems in Asia. Rice is the major staple food for Asians, but the presently grown popular high yielding rice varieties are poor supplier of Zn in their polished form. Breeding rice varieties with high grain Zn has been suggested to be a sustainable, targeted, food-based and cost effective approach in alleviating Zn deficiency. The physiological, genetic and molecular mechanisms of Zn homeostasis have been well studied, but these mechanisms need to be characterized from a biofortification perspective and should be well integrated with the breeding processes. There is a significant variation for grain Zn in rice germplasm and efforts are being directed at exploiting this variation through breeding to develop high Zn rice varieties. Several QTLs and gene specific markers have been identified for grain Zn and there is a great potential to use them in Marker-Assisted Breeding. A thorough characterization of genotype and environmental interactions is essential to identify key environmental factors influencing grain Zn. Agronomic biofortification has shown inconsistent results, but a combination of genetic and agronomic biofortification strategies may be more effective. Significant progress has been made in developing high Zn rice lines for release in target countries. A holistic breeding approach involving high Zn trait development, high Zn product development, product testing and release, including bioefficacy and bioavailability studies is essential for successful Zn biofortification. The online version of this article (doi:10.1186/s12284-016-0122-5) contains supplementary material, which is available to authorized users.
URLPMID:18701340 [本文引用: 1]
The goal of biofortification is to develop plants that have an increased content of bioavailable nutrients in their edible parts. Cereals serve as the main staple food for a large proportion of the world population but have the shortcoming, from a nutrition perspective, of being low in zinc and other essential nutrients. Major bottlenecks in plant biofortification appear to be the root-shoot barrier and - in cereals - the process of grain filling. New findings demonstrate that the root-shoot distribution of zinc is controlled mainly by heavy metal transporting P(1B)-ATPases and the metal tolerance protein (MTP) family. A greater understanding of zinc transport is important to improve crop quality and also to help alleviate accumulation of any toxic metals.
URL [本文引用: 1]
With the aim of identifying rice (Oryza spp.) germplasm having enhanced grain nutritional value, the mineral nutrient and trace element content (a.k.a. ionome) of whole (unmilled) grains from a set of 1763 rice accessions of diverse geographic and genetic origin were evaluated. Seed for analysis of total concentration of the elements P, Mg, K, S, Ca, As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Rb, Sr, Zn by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was produced over two years in Beaumont, Texas, under both flooded and unflooded watering regimes. The distribution of all elements analyzed were skewed toward low grain concentrations. A significant portion of the ionomic variation observed has a genetic basis (broad sense heritabilities 0.14 - 0.75), indicating an ability to breed for improved grain concentration of all elements except nickel. Variation in grain elemental concentrations was not strongly associated with plant height, heading time, or grain shape, suggesting that mechanisms other than these are of primary importance in controlling ionomic variation in rice grain. Accessions high in specific elements were sometimes found to have similar genetic or geographic origins, suggesting they share a heritable mechanism underlying their enhanced ionomes. For example, accessions enhanced for Ca, Mg, or K were more common in the indica than the japonica subgroup; low As was most common among temperate japonica accessions; and several lines high in Mo originated in Malaysia or nearby Brunei.
URL [本文引用: 1]
Plants require the proper balance of zinc (Zn) for normal growth and optimum yield. Interest in Zn has risen in the last decade because Zn deficiency stress is extensive in many areas, causing decreases in crop yields. Zn deficiency also decreases the amount of Zn in cereal grain and diminishes its nutritional quality. Hence, increasing the Zn content of the edible portions of crops should be c...
URLMagsci [本文引用: 1]
<P><FONT face=Verdana>【目的】研究叶面喷施锌铁肥对水稻产量、品质及锌、铁在稻株中分布的影响及品种差异。为研究微量元素锌、铁向籽粒运输存在的障碍提供理论依据。【方法】选用生产上两个推广品种(两优培九和嘉花1号)为试验材料,通过叶面喷施不同浓度的锌、铁肥,分别测定两品种水稻的产量、品质及微量元素锌铁的含量。【结果】叶面喷施锌铁均能提高水稻结实率、千粒重、产量及收获指数,其中叶面喷施组合Zn1Fe1(0.1%ZnSO4,0.15%FeSO4)对两优培九和嘉花1号产量的提高幅度最大,增产分别为4.5%和5.6%。锌、铁对结实率和收获指数的影响存在明显的品种差异。叶面喷施锌、铁肥均使直链淀粉含量显著降低且存在明显品种差异。两品种植酸含量均在喷施组合Zn2Fe0(0.2%ZnSO4)下达最低值。此外,叶面喷施锌铁能够显著提高水稻籽粒锌铁含量,两优培九和嘉花1号均在喷施组合Zn2Fe0(0.2%ZnSO4)时籽粒锌含量达到最高,分别比对照提高69.75%和41.65%。从植株锌铁分配看,随着叶面喷施锌铁浓度的提高,微量元素锌铁在植株各部分的含量都提高,其中颖壳和穗部提高最明显。嘉花1号在积累锌方面与两优培九表现相似,随着喷施浓度提高更多的锌将分配到颖壳中。叶面喷施对两品种铁分布的影响存在显著差异,两优培九在组合Zn2Fe2(0.2%ZnSO4,0.3%FeSO4)时籽粒达到最大铁含量,而嘉花1号在Zn0Fe2(0.3%FeSO4)时达到最大铁含量。【结论】通过叶面生物强化措施可在一定程度上调控籽粒微量元素积累,改善稻米营养品质,提高水稻的产量及产量构成要素。<BR></FONT></P>
URLMagsci [本文引用: 1]
<P><FONT face=Verdana>【目的】研究叶面喷施锌铁肥对水稻产量、品质及锌、铁在稻株中分布的影响及品种差异。为研究微量元素锌、铁向籽粒运输存在的障碍提供理论依据。【方法】选用生产上两个推广品种(两优培九和嘉花1号)为试验材料,通过叶面喷施不同浓度的锌、铁肥,分别测定两品种水稻的产量、品质及微量元素锌铁的含量。【结果】叶面喷施锌铁均能提高水稻结实率、千粒重、产量及收获指数,其中叶面喷施组合Zn1Fe1(0.1%ZnSO4,0.15%FeSO4)对两优培九和嘉花1号产量的提高幅度最大,增产分别为4.5%和5.6%。锌、铁对结实率和收获指数的影响存在明显的品种差异。叶面喷施锌、铁肥均使直链淀粉含量显著降低且存在明显品种差异。两品种植酸含量均在喷施组合Zn2Fe0(0.2%ZnSO4)下达最低值。此外,叶面喷施锌铁能够显著提高水稻籽粒锌铁含量,两优培九和嘉花1号均在喷施组合Zn2Fe0(0.2%ZnSO4)时籽粒锌含量达到最高,分别比对照提高69.75%和41.65%。从植株锌铁分配看,随着叶面喷施锌铁浓度的提高,微量元素锌铁在植株各部分的含量都提高,其中颖壳和穗部提高最明显。嘉花1号在积累锌方面与两优培九表现相似,随着喷施浓度提高更多的锌将分配到颖壳中。叶面喷施对两品种铁分布的影响存在显著差异,两优培九在组合Zn2Fe2(0.2%ZnSO4,0.3%FeSO4)时籽粒达到最大铁含量,而嘉花1号在Zn0Fe2(0.3%FeSO4)时达到最大铁含量。【结论】通过叶面生物强化措施可在一定程度上调控籽粒微量元素积累,改善稻米营养品质,提高水稻的产量及产量构成要素。<BR></FONT></P>
URLPMID:16271501 [本文引用: 1]
Humans require more than 22 mineral elements, which can all be supplied by an appropriate diet. However, the diets of populations subsisting on cereals, or inhabiting regions where soil mineral imbalances occur, often lack Fe, Zn, Ca, Mg, Cu, I or Se. Traditional strategies to deliver these minerals to susceptible populations have relied on supplementation or food fortification programs. Unfortunately, these interventions have not always been successful. An alternative solution is to increase mineral concentrations in edible crops. This is termed 'biofortification'. It can be achieved by mineral fertilization or plant breeding. There is considerable genetic variation in crop species that can be harnessed for sustainable biofortification strategies. Varieties with increased mineral concentrations in their edible portions are already available, and new genotypes with higher mineral densities are being developed.
URL [本文引用: 1]
Zinc (Zn) is an essential component of thousands of proteins in plants, although it is toxic in excess. In this review, the dominant fluxes of Zn in the soil-root-shoot continuum are described, including Zn inputs to soils, the plant availability of soluble Zn2+at the root surface, and plant uptake and accumulation of Zn. Knowledge of these fluxes can inform agronomic and genetic strategies to address the widespread problem of Zn-limited crop growth. Substantial within-species genetic variation in Zn composition is being used to alleviate human dietary Zn deficiencies through biofortification. Intriguingly, a meta-analysis of data from an extensive literature survey indicates that a small proportion of the genetic variation in shoot Zn concentration can be attributed to evolutionary processes whose effects manifest above the family level. Remarkable insights into the evolutionary potential of plants to respond to elevated soil Zn have recently been made through detailed anatomical, physiological, chemical, genetic and molecular characterizations of the brassicaceous Zn hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri.
URLPMID:11525504 [本文引用: 1]
Transition metals such as copper are essential for many physiological processes yet can be toxic at elevated levels. Other metals (e.g. lead) are nonessential and potentially highly toxic. Plants – like all other organisms – possess homeostatic mechanisms to maintain the correct concentrations of essential metal ions in different cellular compartments and to minimize the damage from exposure to nonessential metal ions. A regulated network of metal transport, chelation, trafficking and sequestration activities functions to provide the uptake, distribution and detoxification of metal ions. Some of the components of this network have now been identified: a number of uptake transporters have been cloned as well as candidate transporters for the vacuolar sequestration of metals. Chelators and chaperones are known, and evidence for intracellular metal trafficking is emerging. This recent progress in the molecular understanding of plant metal homeostasis and tolerance is reviewed.
URLPMID:16857279 [本文引用: 5]
Abstract Proper metal transport and homeostasis are critical for the growth and development of plants. In order to potentially fortify plants pre-harvest with essential metals in aid of human nutrition, we must understand not only how metals enter the plant but also how metals are then delivered to the edible portions of the plant such as the seed. In this review, we focus on three metals required by both plants and humans: Cu, Fe and Zn. In particular, we present the current understanding of the molecular mechanisms of Cu, Fe and Zn transport, including aspects of uptake, distribution, chelation and/or sequestration.
URLPMID:14585824 [本文引用: 3]
Transition metals such as Fe, Cu, Mn, and Zn are essential minerals for normal plant growth and development, although they can be toxic when present in excess. Thus, for healthy plant growth, a range of transition metals must be acquired from the soil, distributed around the plant, and their concentrations carefully regulated within different cells and organelles. Membrane transport systems are likely to play a central role in these processes. The application of powerful genetic and molecular techniques has now identified a range of gene families that are likely to be involved in transition metal transport. These include the heavy metal ATPases (HMAs), the Nramps, the cation diffusion facilitator (CDF) family, the ZIP family, and the cation antiporters. This review provides a broad overview of the range of potential transport systems now thought to be involved in the uptake, distribution and homeostasis of transition metals in plants.
URLPMID:3355601 [本文引用: 1]
All organisms have evolved strategies to regulate ion and pH homeostasis in response to developmental and environmental cues. One strategy is mediated by monovalent cation-proton antiporters (CPA) that are classified in two superfamilies. Many CPA1 genes from bacteria, fungi, metazoa, and plants have been functionally characterized; though roles of plant CPA2 genes encoding K(+)-efflux antiporter (KEA) and cation/H(+) exchanger (CHX) families are largely unknown. Phylogenetic analysis showed that three clades of the CPA1 Na(+)-H(+) exchanger (NHX) family have been conserved from single-celled algae to Arabidopsis. These are (i) plasma membrane-bound SOS1/AtNHX7 that share ancestry with prokaryote NhaP, (ii) endosomal AtNHX5/6 that is part of the eukaryote Intracellular-NHE clade, and (iii) a vacuolar NHX clade (AtNHX1-4) specific to plants. Early diversification of KEA genes possibly from an ancestral cyanobacterium gene is suggested by three types seen in all plants. Intriguingly, CHX genes diversified from three to four members in one subclade of early land plants to 28 genes in eight subclades of Arabidopsis. Homologs from Spirogyra or Physcomitrella share high similarity with AtCHX20, suggesting that guard cell-specific AtCHX20 and its closest relatives are founders of the family, and pollen-expressed CHX genes appeared later in monocots and early eudicots. AtCHX proteins mediate K(+) transport and pH homeostasis, and have been localized to intracellular and plasma membrane. Thus KEA genes are conserved from green algae to angiosperms, and their presence in red algae and secondary endosymbionts suggest a role in plastids. In contrast, AtNHX1-4 subtype evolved in plant cells to handle ion homeostasis of vacuoles. The great diversity of CHX genes in land plants compared to metazoa, fungi, or algae would imply a significant role of ion and pH homeostasis at dynamic endomembranes in the vegetative and reproductive success of flowering plants.
URLPMID:3073911 [本文引用: 2]
Background Members of the cation diffusion facilitator (CDF) family are integral membrane divalent cation transporters that transport metal ions out of the cytoplasm either into the extracellular space or into internal compartments such as the vacuole. The spectrum of cations known to be transported by proteins of the CDF family include Zn, Fe, Co, Cd, and Mn. Members of this family have been identified in prokaryotes, eukaryotes, and archaea, and in sequenced plant genomes. CDF families range in size from nine members in Selaginella moellendorffii to 19 members in Populus trichocarpa . Phylogenetic analysis suggests that the CDF family has expanded within plants, but a definitive plant CDF family phylogeny has not been constructed. Results Representative CDF members were annotated from diverse genomes across the Viridiplantae and Rhodophyta lineages and used to identify phylogenetic relationships within the CDF family. Bayesian phylogenetic analysis of CDF amino acid sequence data supports organizing land plant CDF family sequences into 7 groups. The origin of the 7 groups predates the emergence of land plants. Among these, 5 of the 7 groups are likely to have originated at the base of the tree of life, and 2 of 7 groups appear to be derived from a duplication event prior to or coincident with land plant evolution. Within land plants, local expansion continues within select groups, while several groups are strictly maintained as one gene copy per genome. Conclusions Defining the CDF gene family phylogeny contributes to our understanding of this family in several ways. First, when embarking upon functional studies of the members, defining primary groups improves the predictive power of functional assignment of orthologous/paralogous genes and aids in hypothesis generation. Second, defining groups will allow a group-specific sequence motif to be generated that will help define future CDF family sequences and aid in functional motif identification, which currently is lacking for this family in plants. Third, the plant-specific expansion resulting in Groups 8 and 9 evolved coincident to the early primary radiation of plants onto land, suggesting these families may have been important for early land colonization.
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Excessive amounts of nickel (Ni) can be toxic for plants. Recently, we reported that IRT1, the primary iron (Fe) uptake transporter in roots, meditates excess Ni accumulation in Arabidopsis thaliana. We also found that Ni exposure increases IRT1 expression in roots, suggesting that Ni uptake is further induced by Ni stress. Here, we show that Ni exposure induces expression of not only IRT1, but also FRO2, a ferric reductase in the root epidermis, and FIT, a transcription factor regulating the expression of genes involved in Fe homeostasis including IRT1 and FRO2. This result suggests that Ni accumulation induces an Fe-deficient response and leads to the induction of IRT1. Our findings suggest that excess Ni causes Fe deficiency at the molecular level and induces Fe deficiency signaling in plant cells.
URLPMID:10748254 [本文引用: 1]
Members of the ZIP gene family, a novel metal transporter family first identified in plants, are capable of transporting a variety of cations, including cadmium, iron, manganese and zinc. Information on where in the plant each of the ZIP transporters functions and how each is controlled in response to nutrient availability may allow the manipulation of plant mineral status with an eye to (1) creating food crops with enhanced mineral content, and (2) developing crops that bioaccumulate or exclude toxic metals.
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URLPMID:24033183 [本文引用: 1]
High expression of zinc (Zn)-regulated, iron-regulated transporter-like protein (ZIP) genes increases root Zn uptake in dicots, leading to high accumulation of Zn in shoots. However, none of the ZIP genes tested previously in monocots could enhance shoot Zn accumulation. In this report, barley (Hordeum vulgare) HvZIP7 was investigated for its functions in Zn transport. The functions of HvZIP7 in planta were studied using in situ hybridization and transient analysis of subcellular localization with a green fluorescent protein (GFP) reporter. Transgenic barley lines overexpressing HvZIP7 were also generated to further understand the functions of HvZIP7 in metal transport. HvZIP7 is strongly induced by Zn deficiency, primarily in vascular tissues of roots and leaves, and its protein was localized in the plasma membrane. These properties are similar to its closely related homologs in dicots. Overexpression of HvZIP7 in barley plants increased Zn uptake when moderately high concentrations of Zn were supplied. Significantly, there was a specific enhancement of shoot Zn accumulation, with no measurable increase in iron (Fe), manganese (Mn), copper (Cu) or cadmium (Cd). HvZIP7 displays characteristics of low-affinity Zn transport. The unique function of HvZIP7 provides new insights into the role of ZIP genes in Zn homeostasis in monocots, and offers opportunities to develop Zn biofortification strategies in cereals.
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Abstract Micronutrients are important for the growth and development of plants, which deploy families of transporters for their uptake and distribution. We have functionally characterized a novel transition metal ion transporter from rice, OsZIP6 (Oryza sativa zinc regulated transporter, iron regulated transporter-like protein 6). The transporter was found to be transcriptionally activated in shoot and root tissues in response to deficiency in Fe(2+), Zn(2+) and Mn(2+). OsZIP6 was expressed in Xenopus laevis oocytes, where currents were observed on addition of Co(2+), Fe(2+) and Cd(2+) but not Zn(2+), Mn(2+) and Ni(2+). This substrate range for OsZIP6, identified using two-electrode voltage clamp electrophysiology was confirmed by atomic absorption spectroscopy. Ion transport by OsZIP6 was found to be pH dependent and enhanced transport was observed at acidic pH. Radioisotope uptake suggested that Co(2+) competitively inhibits Fe(2+) uptake by OsZIP6. Identification and characterization of ZIP family members from crop plants will contribute to an understanding of nutrient mineral homeostasis in these plants. Copyright 脗漏 2015 Elsevier Masson SAS. All rights reserved.
URLPMID:16263903 [本文引用: 5]
Abstract Zinc (Zn) is an essential element for the normal growth of plants but information is scarce on the mechanisms whereby Zn is transported in rice (Oryza sativa L.) plants. Four distinct genes, OsZIP4, OsZIP5, OsZIP6, and OsZIP7 that exhibit sequence similarity to the rice ferrous ion transporter, OsIRT1, were isolated. Microarray and northern blot analysis revealed that OsZIP4 was highly expressed under conditions of Zn deficiency in roots and shoots. Real-time-PCR revealed that the OsZIP4 transcripts were more abundant than those of OsZIP1 or OsZIP3 in Zn-deficient roots and shoots. OsZIP4 complemented a Zn-uptake-deficient yeast (Saccharomyces cerevisiae) mutant, Deltazrt1,Deltazrt2, indicating that OsZIP4 is a functional transporter of Zn. OsZIP4-synthetic green fluorescent protein (sGFP) fusion protein was transiently expressed in onion epidermal cells localized to the plasma membrane. In situ hybridization analysis revealed that OsZIP4 in Zn-deficient rice was expressed in shoots and roots, especially in phloem cells. Furthermore, OsZIP4 transcripts were detected in the meristem of Zn-deficient roots and shoots. These results suggested that OsZIP4 is a Zn transporter that may be responsible for the translocation of Zn within rice plants.
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Two ZIP (Zrt, Irt-like Protein) cDNAs were isolated from rice (Oryza sativa L.) by RT-PCR approach, and named as OsZIP7a and OsZIP8 respectively. The predicted proteins of OsZIP7a and OsZIP8 consist of 384 and 390 amino acid residues respectively, and display high similarity to other plant ZIP proteins. Each protein contains eight transmembrane (TM) domains and a highly conserved ZIP signature motif, with a histidine-rich region in the variable region between TM domains III and IV. By semi-quantitative RT-PCR approach, it was found that the expression of OsZIP7a was significantly induced in rice roots by iron-deficiency, while that of OsZIP8 induced in both rice roots and shoots by zinc-deficiency. When expressed in yeast cells, OsZIP7a and OsZIP8 could complement an iron-uptake-deficient yeast mutant and a zinc-uptake-deficient yeast mutant respectively. It suggested that the OsZIP7a and OsZIP8 might encode an iron and a zinc transporter protein in rice respectively.
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Developing tissues such as meristem with low transpiration require high Zn levels for their active growth, but the molecular mechanisms underlying the preferential distribution to these tissues are poorly understood. We found that a member of the ZIP (ZRT, IRT-like protein), OsZIP3, showed high expression in the nodes of rice (Oryza sativa). Immunostaining revealed that OsZIP3 was localized at the xylem intervening parenchyma cells and xylem transfer cells of the enlarged vascular bundle in both basal and upper nodes. Neither OsZIP3 gene expression nor encoded protein was affected by either deficiency or toxic levels of Zn. Knockdown of OsZIP3 resulted in significantly reduced Zn levels in the shoot basal region containing the shoot meristem and elongating zone, but increased Zn levels in the transpiration flow. A short-term experiment with the (67) Zn stable isotope showed that more Zn was distributed to the lower leaves, but less to the shoot elongating zone and nodes in the knockdown lines compared with the wild-type rice at both the vegetative and reproductive growth stages. Taken together, OsZIP3 located in the node is responsible for unloading Zn from the xylem of enlarged vascular bundles, which is the first step for preferential distribution of Zn to the developing tissues in rice.
URLPMID:20496122 [本文引用: 3]
Zinc is an essential micronutrient for several physiological and biochemical processes. To investigate its transport in rice, we characterized OsZIP8 , a rice ZIP (Zrt, Irt-like Protein) gene that is strongly up-regulated in shoots and roots under Zn deficiency. OsZIP8 could complement the growth defect of Zn-uptake yeast mutant. The OsZIP8-GFP fusion proteins were localized to the plasma membrane, suggesting that OsZIP8 is a plasma membrane zinc transporter in rice. Activation and overexpression of this gene disturbed the zinc distribution in rice plants, resulting in lower levels in shoots and mature seeds, but an increase in the roots. Field-grown transgenic plants were shorter than the WT. Under treatment with excess zinc, transgenics contained less zinc in their shoots but accumulated more in the roots. Altogether, these results demonstrate that OsZIP8 is a zinc transporter that functions in Zn uptake and distribution. Furthermore, zinc homeostasis is important to the proper growth and development of rice.
URLPMID:17630290 [本文引用: 1]
Zinc (Zn), an essential nutrient in cells, plays a vital role in controlling cellular processes such as growth, development, and differentiation. Although the mechanisms of Zn translocation in rice plants (Oryza sativa) are not fully understood, it has recently received increased interest. OsZIP4 is a Zn transporter that localizes to apical cells. Transgenic rice plants overexpressing the OsZIP4 gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter were produced. The Zn concentration in roots of 35S-OsZIP4 transgenic plants was 10 times higher than in those of vector controls, but it was five times lower in shoots. The Zn concentration in seeds of 35S-OsZIP4 plants was four times lower compared with vector controls. Northern blot analysis and quantitative real-time reverse transcription-PCR revealed transcripts of OsZIP4 expression driven by the CaMV 35S promoter in roots and shoots of 35S-OsZIP4 plants, but levels of endogenous OsZIP4 transcripts were low in roots and high in shoots compared with vector controls. Microarray analysis revealed that the genes expressed in shoots of 35S-OsZIP4 plants coincided with those induced in shoots of Zn-deficient plants. These results indicate that constitutive expression of OsZIP4 changes the Zn distribution within rice plants, and that OsZIP4 is a critical Zn transporter that must be strictly regulated.
URLPMID:20419467 [本文引用: 6]
Abstract Zinc is essential for normal plant growth and development. To understand its transport in rice, we characterized OsZIP5, which is inducible under Zn deficiency. OsZIP5 complemented the growth defect of a yeast Zn-uptake mutant, indicating that OsZIP5 is a Zn transporter. The OsZIP5-GFP fusion protein was localized to the plasma membrane. Transgenic plants overexpressing the gene grew less well. Overexpression of the gene decreased the Zn concentration in shoots, but caused it to rise in the roots. Knockout plants showed no visible phenotypic changes under either normal or deficient conditions. However, they were tolerant to excess Zn and contained less Zn. In contrast, overexpressing transgenics were sensitive to excess Zn. These results indicate that OsZIP5 plays a role in Zn distribution within rice.
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Abstract Cadmium (Cd) accumulation in rice grains is enhanced if ponded water is released from paddy fields during the reproductive stage (intermittent irrigation). The release of ponded water creates aerobic soil conditions under which Cd becomes soluble and iron (Fe) solubility decreases. We hypothesized that Fe shortage in rice induces Fe uptake and translocation and that Cd is also taken up and translocated throughout this process. Hydroponically cultured Fe-deficient rice absorbed more Cd than did Fe-sufficient rice, and the presence of Fe enhanced the translocation of Cd to the shoots. Yeast mutants expressing OsIRT1 and OsIRT2 , which encode the rice Fe 2+ transporter, became more sensitive to Cd, suggesting that Cd was absorbed by OsIRT1 and OsIRT2. We discuss the possibility that Cd accumulation in rice grains during the reproductive stage is mediated by the Fe transport system.
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URLPMID:10394943 [本文引用: 1]
The molecular basis for the transport of manganese across membranes in plant cells is poorly understood. We have found that IRT1, an Arabidopsis thaliana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1螖). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport manganese as well. This manganese uptake activity was inhibited by cadmium, iron(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 cDNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2), and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper uptake-deficient yeast mutant (ctr1), implying that this transporter is not involved in the uptake of copper in plant cells. The expression of IRT1 is enhanced in A. thaliana plants grown under iron deficiency. Under these conditions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.
URLPMID:12084823 [本文引用: 1]
Plants are the principal source of iron in most diets, yet iron availability often limits plant growth. In response to iron deficiency, Arabidopsis roots induce the expression of the divalent cation transporter IRT1. Here, we present genetic evidence that IRT1 is essential for the uptake of iron from the soil. An Arabidopsis knockout mutant in IRT1 is chlorotic and has a severe growth defect in soil, leading to death. This defect is rescued by the exogenous application of iron. The mutant plants do not take up iron and fail to accumulate other divalent cations in low-iron conditions. IRT1-green fluorescent protein fusion, transiently expressed in culture cells, localized to the plasma membrane. We also show, through promoter::beta-glucuronidase analysis and in situ hybridization, that IRT1 is expressed in the external cell layers of the root, specifically in response to iron starvation. These results clearly demonstrate that IRT1 is the major transporter responsible for high-affinity metal uptake under iron deficiency.
URLPMID:12084831 [本文引用: 1]
Iron, an essential nutrient, is not readily available to plants because of its low solubility. In addition, iron is toxic in excess, catalyzing the formation of hydroxyl radicals that can damage cellular constituents. Consequently, plants must carefully regulate iron uptake so that iron homeostasis is maintained. The Arabidopsis IRT1 gene is the major transporter responsible for high-affinity iron uptake from the soil. Here, we show that the steady state level of IRT1 mRNA was induced within 24 h after transfer of plants to iron-deficient conditions, with protein levels peaking 72 h after transfer. IRT1 mRNA and protein were undetectable 12 h after plants were shifted back to iron-sufficient conditions. Overexpression of IRT1 did not confer dominant gain-of-function enhancement of metal uptake. Analysis of 35S-IRT1 transgenic plants revealed that although IRT1 mRNA was expressed constitutively in these plants, IRT1 protein was present only in the roots when iron is limiting. Under these conditions, plants that overexpressed IRT1 accumulated higher levels of cadmium and zinc than wild-type plants, indicating that IRT1 is responsible for the uptake of these metals and that IRT1 protein levels are indeed increased in these plants. Our results suggest that the expression of IRT1 is controlled by two distinct mechanisms that provide an effective means of regulating metal transport in response to changing environmental conditions.
URLPMID:3528025 [本文引用: 2]
A better understanding of the role of the Arabidopsis ZIP family of micronutrient transporters is necessary in order to advance our understanding of plant Zn, Fe, Mn, and Cu homeostasis. In the current study, the 11 Arabidopsis ZIP family members not yet well characterized were first screened for their ability to complement four yeast mutants defective in Zn, Fe, Mn, or Cu uptake. Six of the Arabidopsis ZIP genes complemented a yeast Zn uptake-deficient mutant, one was able partially to complement a yeast Fe uptake-deficient mutant, six ZIP family members complemented an Mn uptake-deficient mutant, and none complemented the Cu uptake-deficient mutant. AtZIP1 and AtZIP2 were then chosen for further study, as the preliminary yeast and in planta analysis suggested they both may be root Zn and Mn transporters. In yeast, AtZIP1 and AtZIP2 both complemented the Zn and Mn uptake mutants, suggesting that they both may transport Zn and/or Mn. Expression of both genes is localized to the root stele, and AtZIP1 expression was also found in the leaf vasculature. It was also found that AtZIP1 is a vacuolar transporter, while AtZIP2 is localized to the plasma membrane. Functional studies with Arabidopsis AtZIP1 and AtZIP2 T-DNA knockout lines suggest that both transporters play a role in Mn (and possibly Zn) translocation from the root to the shoot. AtZIP1 may play a role in remobilizing Mn from the vacuole to the cytoplasm in root stellar cells, and may contribute to radial movement to the xylem parenchyma. AtZIP2, on the other hand, may mediate Mn (and possibly Zn) uptake into root stellar cells, and thus also may contribute to Mn/Zn movement in the stele to the xylem parenchyma, for subsequent xylem loading and transport to the shoot.
URLPMID:15316291 [本文引用: 3]
Abstract To broaden our understanding of micronutrient metal transport in plants, we have identified cDNAs for six new metal transporters in the model legume Medicago truncatula. All of the predicted proteins have high similarity to the ZIP protein family, and have been designated MtZIP1, MtZIP3, MtZIP4, MtZIP5, MtZIP6, and MtZIP7. The six predicted proteins ranged from 350 to 372 amino acids in length; sequence analysis revealed that all proteins contained eight transmembrane domains and the highly conserved ZIP signature motif. Most of the proteins also exhibited a histidine-rich region in the variable sequence between transmembrane domains III and IV. When MtZIPs were transformed into appropriate metal-uptake defective yeast mutants and grown on metal-limited media, MtZIP1, MtZIP5, and MtZIP6 proteins restored yeast growth on Zn-limited media, MtZIP4 and MtZIP7 proteins restored yeast growth on Mn-limited media, and MtZIP3, MtZIP5, and MtZIP6 proteins restored yeast growth on Fe-limited media. Therefore, we conclude that these proteins function as metal transporters in Medicago truncatula. The expression pattern for each gene was studied by semi-quantitative RT-PCR in roots and leaves from plants grown under various metal supplies. MtZIP1 transcripts were only detected in Zn-deficient roots and leaves. MtZIP3 and MtZIP4 expression was down regulated in leaves from Mn- and Fe-deficient plants and appeared to be upregulated under Zn-deficient conditions in both roots and leaves. MtZIP5 was upregulated in leaves under Zn and Mn deficiency. The expression of MtZIP6 and MtZIP7 was unaffected by the metal supply, at least in root and leaf tissues. Characterizing these proteins in a single organism will allow us to understand the interplay between various ZIP genes, and the role they play in the regulation/execution of plant metal homeostasis.
URLPMID:19249224 [本文引用: 1]
Abstract Zinc (Zn) is an essential element for plants but limited information is currently available on the molecular basis for Zn(2+) transport in crop species. To expand the knowledge on Zn(2+) transport in barley (Hordeum vulgare L.), a cDNA library prepared from barley roots was expressed in the yeast (Saccharomyces cerevisiae) mutant strain Deltazrt1/Deltazrt2, defective in Zn(2+) uptake. This strategy resulted in isolation and identification of three new Zn(2+) transporters from barley. All of the predicted proteins have a high similarity to the ZIP protein family, and are designated HvZIP3, HvZIP5 and HvZIP8, respectively. Complementation studies in Deltazrt1/Deltazrt2 showed restored growth of the yeast cells transformed with the different HvZIPs, although with different efficiency. Transformation into Fe(2+) and Mn(2+) uptake defective yeast mutants showed that the HvZIPs were unable to restore the growth on Fe(2+) and Mn(2+) limited media, respectively, indicating a specific role in Zn(2+) transport. In intact barley roots, HvZIP8 was constitutively expressed whereas HvZIP3 and HvZIP5 were mainly expressed in -Zn plants. These results suggest that HvZIP3, HvZIP5 and HvZIP8 are Zn(2+) transporters involved in Zn(2+) homeostasis in barley roots. The new transporters may facilitate breeding of barley genotypes with improved Zn efficiency and Zn content.
URLPMID:24953837 [本文引用: 5]
Mineral elements, including both essential and toxic elements, are delivered to different tissues after they are taken up from the roots, but the mechanism (or mechanisms) underlying the distribution remains poorly understood. In graminaceous plants, this distribution occurs in nodes, which have a complex, well-organized vascular system. A transfer of mineral elements between different vascular bundles is required, especially for preferential distribution to developing tissues that have low transpiration but high nutrient requirements. This intervascular transfer is mediated by various transporters localized at different cells in the node. In this opinion article, we propose four modes of distribution for different mineral elements: xylem-switch, phloem-tropic, phloem-kickback, and minimum-shift, based on specific molecular transport processes identified in the nodes mainly of rice (Oryza sativa). We also discuss the prospects for future studies on mineral nutrient distribution in the nodes.
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When rice plants were grown in a solution containing 0.025 ppm 65Zn and 0.25 ppm 54Mn, there was a strong accumulation of 65Zn in the base of actively elongating young and emergent leaf sheaths and blades, and in the young panicle, while 65Zn accumulation in the sheath and blade of older leaves was considerable. Strong 65Zn accumulation was also noted at the base of the elongating internode, wh...
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Accurate and plain maps on the vascular bundles of the dwarf part of stem inthe rice plant are illustrated in fig. 1 and 2. The vascular network of the dwarf part of stem presents striking similarity to that of the elongated part of stem on the point of histogenic view. In the swelling elliptical leaf traces of the dwarf part of stem as well as the elongated part of stem, trachieds and xylem parenchyma, containing xylem transfer cells, display a mosaic structure. But, no phloem transfer cell has been found throughout the entire stem. When a leaf is emerging out, the swelling elliptical portions of the leaf traces elaborate their xylem structure, in which xylem parenchyma and transfer cells absorb solutes from transpiration stream and send them toward the shoot apex. This function of the swelling xylem structure was verified by the distribution in the stem of barium absorbed through the roots. The vascular bundles of the stem are classified in which these types, from fig.6, in which these types, from fig.6-1 to fig.6-5, have gradually increasing efficiency with regard to horizontal transport
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Zinc deficiency remarkably depressed the zinc concentrations in the meristematic tissues of rice plants. When the zinc concentration was decreased to a level of less than 100 ppm, disorders of the nitrogen metabolism appeared. Zinc deficiency severely depressed the production of proteins in meristematic tissues and brought about the accumulation of free amino acids and ami des (above all, asparagine, glutamine, and alanine). Two-dimensional separation patterns of proteins obtained by O090005Parrell090005s technique suggested that the composition of the proteins remained almost unchanged although their amount was remarkably reduced.
URLPMID:3346231 [本文引用: 2]
Heavy metals are transported to rice grains via the phloem. In rice nodes, the diffuse vascular bundles (DVBs), which enclose the enlarged elliptical vascular bundles (EVBs), are connected to the panicle and have a morphological feature that facilitates xylem-to-phloem transfer. To find a mechanism for restricting cadmium (Cd) transport into grains, the distribution of Cd, zinc (Zn), manganese (Mn), and sulphur (S) around the vascular bundles in node I (the node beneath the panicle) ofOryza sativa鈥楰oshihikari鈥 were compared 1 week after heading. Elemental maps of Cd, Zn, Mn, and S in the vascular bundles of node I were obtained by synchrotron micro-X-ray fluorescence spectrometry and electron probe microanalysis. In addition, Cd K-edge microfocused X-ray absorption near-edge structure analyses were used to identify the elements co-ordinated with Cd. Both Cd and S were mainly distributed in the xylem of the EVB and in the parenchyma cell bridge (PCB) surrounding the EVB. Zn accumulated in the PCB, and Mn accumulated around the protoxylem of the EVB. Cd was co-ordinated mainly with S in the xylem of the EVB, but with both S and O in the phloem of the EVB and in the PCB. The EVB in the node retarded horizontal transport of Cd toward the DVB. By contrast, Zn was first stored in the PCB and then efficiently transferred toward the DVB. Our results provide evidence that transport of Cd, Zn, and Mn is differentially controlled in rice nodes, where vascular bundles are functionally interconnected.
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URLPMID:23575418 [本文引用: 1]
Developing tissues such as meristems and reproductive organs require high zinc, but the molecular mechanisms of how zinc taken up by the roots is preferentially delivered to these tissues with low transpiration are unknown. Here, we report that rice (Oryza sativa) heavy metal ATPase2 (OsHMA2), a member of P-type ATPases, is involved in preferential delivery of zinc to the developing tissues in rice. OsHMA2 was mainly expressed in the mature zone of the roots at the vegetative stage, but higher expression was also found in the nodes at the reproductive stage. The expression was unaffected by either zinc deficiency or zinc excess. OsHMA2 was localized at the pericycle of the roots and at the phloem of enlarged and diffuse vascular bundles in the nodes. Heterologous expression of OsHMA2 in yeast (Saccharomyces cerevisiae) showed influx transport activity for zinc as well as cadmium. Two independent Tos17 insertion lines showed decreased zinc concentration in the crown root tips, decreased concentration of zinc and cadmium in the upper nodes and reproductive organs compared with wild-type rice. Furthermore, a short-term labeling experiment with (67)Zn showed that the distribution of zinc to the panicle and uppermost node I was decreased, but that, to the lower nodes, was increased in the two mutants. Taken together, OsHMA2 in the nodes plays an important role in preferential distribution of zinc as well as cadmium through the phloem to the developing tissues.
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Abstract The effect of Zn deficiency in wheat ( Triticum aestivum L. cv. Ares) on the release of Zn mobilizing root exudates was studied in nutrient solution. Compared to Zn sufficient plants, Zn deficient plants had higher root and lower shoot dry weights. After visual Zn deficiency symptoms in leaves appeared (15鈥17 day old plants) there was a severalfold increase in the release of root exudates efficient at mobilizing Zn from either a selective cation exchanger (Zn-chelite) or a calcareous soil. The release of these root exudates by Zn deficient plants followed a distinct diurnal rhythm with a maximum between 2 and 8 h after the onset of light. Re-supply of Zn to deficient plants depressed the release of Zn mobilizing root exudates within 12 h to about 50%-, and after 72 h to the level of the control plants (Zn sufficient plants). The root exudates of Zn deficient wheat plants were equally effective at mobilizing Fe from freshly precipitated Fe III hydroxide as Zn from Zn-chelite. Furthermore, root exudates from Fe deficient wheat plants mobilized Zn from Zn-chelite, as well as Fe from Fe III hydroxide. Purification of the root exudates and identification by HPLC indicated that under Zn as well as under Fe deficiency, wheat roots of the cv. Ares released the phytosiderophore 2鈥-deoxymugineic acid. Additional experiments with barley ( Hordeum vulgare L. cv. Europa) showed that in this species another phytosiderophore (epi-3-hydroxymugineic acid) was released under both Zn and Fe deficiencies. These results demonstrate that the enhanced release of phytosiderophores by roots of grasses is not a response mechanism specific for Fe deficiency, but also occurs under Zn deficiency. The ecological relevance of enhanced release of phytosiderophore also under Zn deficiency is discussed.
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To determine the responses of plants to deficiencies of multiple metals, tobacco plants ( Nicotiana tabacum L.) were subjected to treatments that were deficient in combinations of Fe and two other micronutrients, Zn and Mn. The response was measured using macro indices, including plant appearance, FW, chlorophyll concentration, and mineral concentrations, and with a molecular index, the barley ( Hordeum vulgare L.) Ids2 promoter / GUS fusion gene system (Yoshihara et al. 2003, Plant Biotech 20: 33鈥41). Tobacco plants grown in medium with combined deficiencies grew better and had higher chlorophyll concentrations than did plants grown on medium deficient in Fe only, although the measured Fe concentrations in the plant tissues were essentially the same. The Ids2/GUS expression responded to Fe deficiency, but not to Mn or Zn deficiencies in tobacco plants when Fe was present. Tobacco plants grown in medium with combined deficiencies had clearly detectable GUS activity, but the response was significantly lower than that in tobacco plants deficient in Fe only. The Fe-deficiency symptoms were mitigated at both the visible and molecular levels. Although more precise experimental evidence is needed to explain the mitigation mechanism, the balance of minerals was shown to be an important parameter to consider when estimating iron deficiency based on tobacco plant responses.
URL [本文引用: 1]
URL [本文引用: 1]
水稻在长期的自然进化和人工选择过程中积累了大量自然变异,这些自然变异是许多重要农艺性状的遗传基础,也是水稻育种筛选的主要目标.近些年,随着分子技术的发展,水稻自然变异研究取得了一系列重要突破.本文结合最新研究进展,系统介绍了水稻自然变异的特点及相应分析方法,并强调了高通量测序技术在今后水稻自然变异挖掘中的意义;对最近10年来报道的抽穗期、产量元件及抗逆和驯化相关性状自然变异的分子机制及驯化特征进行了详细说明;结合这些自然变异的分子特征,总结了利用不同变异类型改良现有品种的方法,为今后分子育种提供理论依据.
URL [本文引用: 1]
水稻在长期的自然进化和人工选择过程中积累了大量自然变异,这些自然变异是许多重要农艺性状的遗传基础,也是水稻育种筛选的主要目标.近些年,随着分子技术的发展,水稻自然变异研究取得了一系列重要突破.本文结合最新研究进展,系统介绍了水稻自然变异的特点及相应分析方法,并强调了高通量测序技术在今后水稻自然变异挖掘中的意义;对最近10年来报道的抽穗期、产量元件及抗逆和驯化相关性状自然变异的分子机制及驯化特征进行了详细说明;结合这些自然变异的分子特征,总结了利用不同变异类型改良现有品种的方法,为今后分子育种提供理论依据.
URLPMID:25274737 [本文引用: 1]
Rice Variation Map (RiceVarMap, http:/ricevarmap.ncpgr.cn) is a database of rice genomic variations. The database provides comprehensive information of 6,551,358 single nucleotide polymorphisms (SNPs) and 1,214,627 insertions/deletions (INDELs) identified from sequencing data of 1479 rice accessions. The SNP genotypes of all accessions were imputed and evaluated, resulting in an overall missing data rate of 0.42% and an estimated accuracy greater than 99%. The SNP/INDEL genotypes of all accessions are available for online query and download. Users can search SNPs/INDELs by identifiers of the SNPs/INDELs, genomic regions, gene identifiers and keywords of gene annotation. Allele frequencies within various subpopulations and the effects of the variation that may alter the protein sequence of a gene are also listed for each SNP/INDEL. The database also provides geographical details and phenotype images for various rice accessions. In particular, the database provides tools to construct haplotype networks and design PCR-primers by taking into account surrounding known genomic variations. These data and tools are highly useful for exploring genetic variations and evolution studies of rice and other species.
