Genome-wide Investigation of micro RNAs and Their Targets in Brassica rapa ssp. pekinensis Root with Plasmodiophora brassicae Infection

Increasing evidence has revealed that micro RNAs play a pivotal role in the post transcriptional regulation of gene expression in response to pathogens in plants. However, there is little information available about the expression patterns of mi RNAs and their targets in Chinese cabbage(Brassica rapa ssp. pekinensis) under Plasmodiophora brassicae stress. In the present study, using deep sequencing and degradome analysis, a genome-wide identification of mi RNAs and their targets during P. brassicae stress was performed. A total of 221 known and 93 potentially novel mi RNAs were successfully identified from two root libraries of one control(635-10CK) and P. brassicae-treated Chinese cabbage samples(635-10T). Of these, 14 known and 10 potentially novel mi RNAs were found to be differentially expressed after P. brassicae treatment. Degradome analysis revealed that the 223 target genes of the 75 mi RNAs could be potentially cleaved. KEGG(Kyoto Encyclopedia of Genes and Genomes)pathway analysis suggested that the putative target genes of the mi RNAs were predominately involved in selenocompound metabolism and plant hormone signal transduction. Then the expression of 12 mi RNAs was validated by quantitative real-time PCR(q RT-PCR). These results provide insights into the mi RNA-mediated regulatory networks underlying the stress response to the plant pathogen P. brassicae.