Overexpression of OsNINJA1-interacting protein OsFHA1 affects jasmonate-mediated OsMYC2 signaling but not disease resistance in rice

Jasmonic acid (JA) is a plant hormone that regulates rice growth and development. The rice protein NOVEL INTERACTOR OF JAZ1 (OsNINJA1) acts as a repressor of JA signaling by forming a complex with JASMONATE ZIM-domain (JAZ) proteins, but the role of OsNINJA1-interacting proteins in JA signaling in rice remains unclear. In the present study on the role of the OsNINJA1-interacting protein, forkhead-associated (FHA) domain-containing protein1 (OsFHA1), in JA signaling in rice, the expression of OsFHA1 was downregulated after treatment with JA. Among the 15 OsJAZ proteins in rice, OsFHA1 interacted only with OsJAZ2. Resistance against rice bacterial blight was induced by JA in OsFHA1-overexpressing plants and in the wild-type (WT) plants. The expression of JA-mediated OsMYC2-dependent defense-related genes that are induced early (4 h) was not upregulated by JA treatment in OsFHA1-overexpressing plants. Conversely, the expression of JA-mediated OsMYC2-independent defense-related genes induced later (24 h) was upregulated by JA treatment in OsFHA1-overexpressing plants and in WT plants. These results suggest that OsFHA1 is a negative regulator only of OsMYC2-mediated JA signaling in rice.