The overexpression of OsSRO1a, which encodes an OsNINJA1- and OsMYC2-interacting protein, negatively affects OsMYC2-mediated jasmonate signaling in rice.

KEY MESSAGE: OsNINJA1-interacting protein, OsSRO1a, acts as a mediator that suppresses OsMYC2 activity in response to JA. Jasmonic acid (JA) is an important plant hormone for the stable growth and development of higher plants. The rice gene NOVEL INTERACTOR OF JAZ1 (OsNINJA1) interacts with Jasmonate ZIM-domain (JAZ) proteins and is a repressor of JA signaling. In this study, we identified several OsNINJA1-interacting proteins in rice from a yeast two-hybrid screen. Among the newly identified genes, we focused on SIMILAR TO RCD ONE1a (OsSRO1a) and investigated its role in JA signaling. Full-length OsSRO1a interacted with OsNINJA1 in plant cells but not in yeast cells. OsSRO1a also interacted with OsMYC2, a positive transcription factor in JA signaling, in both plant and yeast cells. The expression of OsSRO1a was upregulated at a late phase after JA treatment. Transgenic rice plants overexpressing OsSRO1a exhibited JA-insensitive phenotypes. In wild-type plants, JA induces resistance against rice bacterial blight, but this phenotype was suppressed in the OsSRO1a-overexpressing plants. Furthermore, the degradation of chlorophyll under dark-induced senescence conditions and the JA-induced upregulation of OsMYC2-responsive genes were suppressed in the OsSRO1a-overexpressing plants. These results suggest that OsSRO1a is a negative regulator of the OsMYC2-mediated JA signaling pathway in rice.