A novel potato microRNA stu-miR856 regulates mitogen-activatedprotein kinase genes contributing to drought tolerance

Mitogen-activated protein kinases (MAPKs) are significant components of MAPK cascades, which play versatile roles in different transduction pathways to mediate stress adaptation. However, little information is known about post-transcriptional regulation of MAPK genes in plant under drought stress. MicroRNAs (miRNAs), a class of newly identified, short non-coding RNAs, regulate the expression of target genes in plant growth, development, and stress responses. In order to investigate the mechanism of miRNA regulating MAPK genes in potato, we identified a novel potato miRNA with the sequence CGGCCTTAATAAGATGGTGAAG and named it as stu-miR856 depending on miRNA deep sequencing and bioinformatic analysis. Target prediction indicates that it can bind to the coding sequence region of two potato MAPK-like genes, and cleavage positions of them were also effectively validated by RNA ligase-mediated 5' rapid amplification of cDNA ends assay. In addition, expressional analysis shows that stu-miR856 and its targets exhibited an opposite expression pattern: stu-miR856 expression significantly decreased while its target genes greatly increased in the different stages of drought treatment. The results indicate that a decreased expression of stu-miR856 might drive overexpression of two StMAPK genes family members, which may contribute to regulation of the drought adaptation of potato plants.