The dsRNA-binding protein OsDRB1.4 is phosphorylated by OsMPK5 and negatively regulates rice defense against Magnaporthe oryzae

Abstract

Plant mitogen-activated protein kinases (MAPKs) are pivotal regulators of the innate immune signaling pathway and phosphorylate an array of transcription factors to reprogram the expression of disease-responsive genes. However, how MAPKs reprogram plant gene expression at the posttranscriptional level is poorly understood. Here, we show that double-stranded RNA-binding protein 1.4 (OsDRB1.4) is a substrate of OsMPK5 in rice. OsDRB1.4 belongs to a monocot-specific subgroup of the DRB family and contains a noncanonical MAPK interaction motif in its C terminus. OsMPK5 mainly phosphorylates the 216th serine of OsDRB1.4 in vivo. Silencing and knockout of OsDRB1.4 increased rice defense against Magnaporthe oryzae and increased the expression of 34 genes, including PR5 and three R-GENE ANALOG genes, whereas OsDRB1.4-overexpressing rice was more susceptible to blast disease. In contrast, overexpressing OsDRB1.4 with the phosphorylation sites mutated in rice did not affect disease susceptibility, suggesting that these phosphorylation sites are critical for OsDRB1.4 functionality. A total of 130 transcript units and 171 annotated repetitive sequence transcripts were identified as the RNA partners of OsDRB1.4 through targeted RNA editing. RNA electrophoretic mobility shift assays validated that OsDRB1.4 directly bound the stem-loop dsRNAs of microRNA precursors and the 3′-UTRs of protein-coding mRNAs. Further analysis indicated that OsDRB1.4 positively regulated the expression of mature osa-miR7695 and osa-miR2871. More importantly, OsDRB1.4 bound stem-loop dsRNA in the 3′-UTR of Pi-ta RESISTANCE (Ptr) and negatively affected protein expression. Together, our data reveal that the OsMPK5-OsDRB1.4 module negatively regulates rice defense against M. oryzae through the posttranscriptional suppression of defense-related genes.