Identification and Validation of miRNAs Associated with the Resistance of Maize (Zea mays L.) to Exserohilum turcicum

Northern leaf blight, caused by the fungus Exserohilum turcicum (Pass.), is a major disease of maize (Zea mays L.). MicroRNAs (miRNAs) have been recently reported as gene expression regulators related to several stress responses; however, evidence of the role of miRNAs in plant response to biotic stresses is limited. In this study, the miRNA expression patterns in maize in response to E. turcicum stress were investigated using a plant miRNA microarray platform. A total of 118 miRNAs were detected in mock- and E. turcicum-inoculated leaves. Among these miRNAs, miR530, miR811, miR829, and miR845 were identified as new miRNAs in maize through a homology-based approach. The secondary structures and putative targets of these miRNAs were also predicted. In addition, four miRNAs were differentially regulated in response to E. turcicum: miR811, miR829, miR845, and miR408. The functional annotation of the predicted targets indicated that these stress-responsive miRNAs regulate metabolic, morphologic, and physiologic adaptations in maize seedlings at the post-transcriptional level. Four targets were negatively correlated with their corresponding miRNAs (miR811, miR829, and miR408). Furthermore, we have demonstrated for the first time that miR811 and miR829 confers a high degree of resistance to E. turcicum, which can be used in maize breeding programs.

玉米北方叶枯病（Northern leaf blight）是由大斑突脐蠕孢菌（Exserohilum turcicum (Pass.)）引发的玉米（Zea mays L.）主要病害。微小RNA（microRNAs, miRNAs）作为一类基因表达调控因子，近年研究证实其参与多种胁迫响应过程，但目前关于miRNA在植物应对生物胁迫中的作用证据仍较为匮乏。本研究借助植物miRNA微阵列平台，探究了玉米响应E. turcicum胁迫的miRNA表达谱。研究在模拟接种与E. turcicum接种的玉米叶片中共检测到118个miRNAs，其中通过同源比对法鉴定出4个玉米新miRNA：miR530、miR811、miR829与miR845。本研究同时预测了这些miRNAs的二级结构与潜在靶标基因。此外，有4个miRNAs在响应E. turcicum胁迫时呈现差异表达，分别为miR811、miR829、miR845与miR408。对预测靶标的功能注释结果显示，这些胁迫响应miRNAs可通过转录后调控途径，参与调控玉米幼苗的代谢、形态及生理适应性过程。其中4个靶标与对应的miRNAs（miR811、miR829与miR408）呈负调控关系。本研究还首次证实，miR811与miR829可赋予玉米对E. turcicum的高抗性，该研究成果可应用于玉米育种项目中。