DIFFERENTIALLY EXPRESSED miRNAs POTENTIALLY INVOLVED IN THE REGULATION OF DEFENSE MECHANISM TO DROUGHT STRESS IN MAIZE SEEDLINGS

Maize employs complex mechanisms of gene regulation in response to drought stress. Micro-RNAs (miRNAs) have emerged as a novel regulatory mechanism of gene expression. Drought induces upregulation and downregulation of numerous genes. However, little is known about the role of miRNAs in maize drought response. In this research, miRNA microarray hybridization showed that 34 miRNAs from 13 plant miRNA families had significantly altered expression after drought treatment. Most of the miRNA-mediated target genes contained a cis-acting element that responded to phytohormone (ABA) stimuli during drought stress. Drought stress-upregulated miR474 could downregulate target gene PDH, which is a negative regulator of proline accumulation, to improve osmoprotection responses to drought stress. On the other hand, drought-downregulated miRNAs (such as miR168, miR528, and miR167) might result in accumulation of their target mRNAs (MAPK, POD, and PLD) to initiate the regulation of ABA-induced stomatal movement and antioxidant defense.