Rice bacterial blight disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most severe diseases of rice. However, the regulatory mechanisms of rice defense against Xoo remain poorly understood. The rice MEDIATOR25, OsMED25-a subunit of the mediator multiprotein complex that acts as a universal adaptor between transcription factors (TFs) and RNA polymerase II-plays an important role in jasmonic acid (JA)-mediated lateral root development in rice. In this study, we found that OsMED25 also plays an important role in JA- and auxin-mediated resistance responses against rice bacterial blight. The osmed25 loss-of-function mutant exhibited high resistance to Xoo. The expression of JA-responsive defense-related genes regulated by OsMYC2, which is a positive TF in JA signaling, was downregulated in osmed25 mutants. Conversely, expression of some OsMYC2-independent JA-responsive defense-related genes was upregulated in osmed25 mutants. Furthermore, OsMED25 interacted with some AUXIN RESPONSE FACTORS (OsARFs) that regulate auxin signaling, whereas the mutated osmed25 protein did not interact with the OsARFs. The expression of auxin-responsive genes was downregulated in osmed25 mutants, and auxin-induced susceptibility to Xoo was not observed in osmed25 mutants. These results indicate that OsMED25 plays an important role in the stable regulation of JA- and auxin-mediated signaling in rice defense response.
Keywords: Xanthomonas oryzae pv. oryzae; auxin; jasmonic acid; mediator; rice.