Regulation and functional role of Arabidopsis miR163 and its targets in plant defense

In plants, microRNAs (miRNAs) have emerged as important regulators in various aspects of growth and development. miR163, a recently evolved miRNA, is highly accumulated in Arabidopsis thaliana but is nearly undetectable in its related outcrossing relative, Arabidopsis arenosa. It has been showed that miR163 plays a role in conferring natural variation of secondary metabolites accumulation in Arabidopsis polyploids. miR163 and its targets expression can be induced by alamethicin (fungal elicitor) treatment. In addition, one of the miR163 targets, farnesoic acid methyltransferase (FAMT) can convert farnesoic acid (FA) to methyl farnesoate (MeFA) to which MeFA is a precursor of insect juvenile hormone III (JHIII). Therefore, these data suggested a role of miR163 and its target in plant defense. However, their physiological relevance in plant defense against biotic stresses is still unclear. The goal of this study is to elucidate the functional roles of Arabidopsis miR163 and its targets in plant defense against bacterial pathogens. We will first evaluate the dynamic and epigenetic regulation of miR163 and its targets under biotic stresses by using wild type A. thaliana, the mir163 mutant and an established MIR163 promoter-GUS reporter transgenic lines. In addition, by overexpressing miR163 or its targets in transgenic A. thaliana, we will examine their direct functional roles in defense against Pseudomonas syringae (Pst). At a biochemical level, alteration of metabolite profiles mediated by miR163 will be characterized using high performance liquid chromatography (HPLC) and mass spectrometry (MS) analyses. Potential gene regulatory network and transcriptome changes mediated by miR163 and its target genes in response to Pst infection will be evaluated using mRNA-seq on genome-wide scale. It is expected that results will shed light on the role of miR163 in plant defenses. Moreover, data obtained will provide a foundation for further investigation on the role of miR163 and its targets in the related Arabidopsis autotetraploids and their tetraploid hybrids, as well as providing insights to the evolutionary significance of miRNA in mediating plant defense pathways in different plant species or hybrids.