MicroRNA biogenesis factor DRB1 is a phosphorylation target of mitogen activated protein kinase MPK3 in both rice and Arabidopsis

MicroRNA (miRNA) biogenesis requires AtDRB1 (double-stranded RNA binding protein)/HYL1 (Hyponastic Leaves1) protein for processing and maturation of miRNA precursors. The AtDRB1/HYL1 protein associates with AtDCL1 (Dicer-Like1) and accurately processes primary-miRNAs (pri-mRNAs) first to precursor-miRNAs (pre-miRNAs) and finally to mature miRNAs. The dephosphorylation of AtDRB1/HYL1 protein is very important for the precise processing of miRNA precursors. The monocot model crop plant Oryzasativa encodes four orthologues of AtDRB1/HYL1 protein, the only one encoded by Arabidopsis thaliana. The present study focuses on the functionality of the O.sativa DRBs as the orthologues of AtDRB1/HYL1 by using RNA binding assays and inplanta protein-protein interaction analysis. Further, mitogen-activated protein kinase MPK3 is established as the kinase phosphorylating DRB1 protein in both the model plants, O.sativa and Arabidopsis. MicroRNA microarray analysis in atmpk3 and atmpk6 mutants indicate the importance of AtMPK3 in maintaining the level of miRNAs in the plant.