Plant hormone jasmonic acid (JA) has been recognized as a signal molecule produced by various stresses such as wounding and pathogen attack and mediates defense reactions. We previously identified a JA-early responsive bHLH factor RERJ1, and reported that the RERJ1 overexpression showed up-regulations of many pathogenesis-related (PR) genes in rice cells and severe growth inhibition in the rice plants. However, biological function of the RERJ1 in rice plants is still unknown. We therefore conducted histochemical analyses of RERJ1 promoter-GUS transgenic plants, and characterized a Tos17 mutant of RERJ1 (rerj1-tos). The inductive expression of RERJ1 was observed in the defined area to be wounded within 2 hours, suggesting that RERJ1 functions at the sites injured by insect herbivory, for example. It has been known that JA is produced at narrow area in leaves by insect herbivory, which arrows plants to emit volatile terpenoids. Therefore, we examined expression of a monoterpene linalool synthetic gene OsLS in the rerj1-tos mutant and JA-deficient mutants. The OsLS gene, which maximally expresses at 2 to 4 hours after wounding in wild-type plants, was significantly less expressed in the rerj1-tos mutant, and also the expression was totally disappeared in the JA-deficient mutants. These results suggest that RERJ1 is induced by synthesized JA at injured sites, then functions to transactivate many PR genes, including the OsLS gene in rice plants.
