Biological Function of the JA-inductive bHLH Transcription Factor RERJ1 in Rice Defense Responses

Abstract

Plant hormone jasmonic acid (JA) has been recognized as a signal molecule that is induced by various stresses such as wounding and pathogen attack and mediates defense reactions. We previously identified the JA-early responsive bHLH factor RERJ1, but its biological function in rice plants has been unknown. Here we conducted histochemical analyses using RERJ1 promoter-GUS transgenic plants, and characterized a rerj1-tos17 mutant. The inductive expression of RERJ1 was observed in the defined area to be wounded within 15 min, suggesting that RERJ1 functions at the sites injured by insect herbivory, for example. Transcriptome analysis of JA-treated rerj1-tos17 mutant indicated that JA-inductive expressions of defense-related genes, such as proteinase inhibitors genes, were severely suppressed in the mutant. These results suggest that RERJ1 is induced by JA at injured sites, then functions to transactivate many defense-related genes in rice. Now bioassays for insect resistance are being conducted with the rerj1-tos17 mutant.