Fusarium ear rot (FER) caused by Fusarium verticillioides is one of the most common diseases affecting maize production worldwide. FER results in severe yield losses and grain contamination with health-threatening mycotoxins. Although most studies to date have focused on comprehensive analysis of gene regulation in maize during defense responses against F. verticillioides infection, less is known about the role of microRNAs (miRNAs) in this process. We used deep sequencing to compare small RNA libraries from the maize kernels of susceptible (N6) or resistant (BT-1) inbred lines from uninfected plants and upon F. verticillioides infection. We found that pathogen exposure was accompanied by dynamic alterations in expression levels of multiple miRNAs, including new members of previously annotated miRNA families. A combination of transcriptomic, degradomic, and bioinformatics analyses revealed that F. verticillioides-responsive miRNAs and their potential target genes displayed opposite expression patterns in the susceptible and resistant genotypes. Functional category analysis uncovered preferential enrichment of the pathogen-responsive miRNAs and their targets in the phenylpropanoid metabolic processes, plant–pathogen interactions, and plant phytohormone signal transduction pathways. Furthermore, transgenic maize plants overexpressing miR408b exhibited reduced resistance to F. verticillioides infection in a susceptible maize line. These findings provide new insights into the regulatory roles of miRNAs in maize immunity against FER and new resources for breeding disease resistance into maize.
拟轮枝镰孢菌引起的玉米穗粒腐病是一种世界性的真菌病害，它不仅造成玉米严重减产，而且病原菌产生的毒素严重威胁人畜健康安全。诸多研究表明玉米穗粒腐病抗性是复杂的数量性状，其中涉及到众多的基因调控网络，利用图位克隆方法鉴定了许多与玉米穗粒腐病抗性相关的QTL及候选抗病基因。但是，关于microRNA是否在转录后水平参与调控玉米穗粒腐病还不清楚。该研究利用穗粒腐病高抗自交系（BT-1）和感病自交系（N6）为材料，通过高通量测序比较分析两种材料籽粒在拟轮枝镰孢菌侵染前后microRNA的特异性表达，鉴定出一系列可能与穗粒腐病抗性相关的microRNA，它们显著富集在已知抗病QTL位点，并且调控植物抗病免疫通路中一些关键的因子。利用降解组和转录组分析其调控的下游靶基因，发现这些差异表达的靶基因主要与苯丙素代谢通路、植物激素信号传导等通路密切相关。最后，选择一个在抗感玉米自交系之间差异表达，并在植物中高度保守的miR408b进行转基因功能分析，发现miR408b的过量积累显著升高对拟轮枝镰孢菌的敏感性，说明其可能是穗粒腐病抗性的一个负调控因子。这些结果有助于从基因转录后调控水平阐明玉米穗粒腐病抗病遗传机制，为抗病玉米选育提供更丰富的育种元件及潜在的分子标记。





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