ERECT LEAF1 suppresses jasmonic acid response in rice by decreasing OsWRKY4 stability.

ERECT LEAF 1 (ELF1), which was identified as a component of brassinosteroid signaling in rice, is involved in brassinosteroid-mediated suppression of jasmonic acid response. Here, by conducting yeast two-hybrid assay and in vitro ubiquitination experiments, we demonstrate that ELF1 interacts with the OsWRKY4 transcription factor, a positive regulator of defense responses to rice sheath blight. ELF1 decreased the stability of OsWRKY4, whereas exogenous jasmonic acid treatment suppressed this effect of ELF1, resulting in OsWRKY4 accumulation in rice plants. In wild-type rice, OsWRKY4 expression was up-regulated by jasmonic acid treatment but down-regulated by brassinosteroid treatment, suggesting that jasmonic acid-induced OsWRKY4 accumulation was caused by a combination of increased production and suppressed degradation. The expression levels of the OsWRKY4 target genes, PR1b and PR5, seemed to be correlated with the OsWRKY4 level. These results suggest that ELF1 indirectly controls the expression of PR1b and PR5 genes by regulating the OsWRKY4 protein level, and support a hypothesis that brassinosteroid and jasmonic acid cooperate to maintain the balance between growth and defense responses. We conclude that ELF1 participates in the antagonistic interaction between these two phytohormones by suppressing the jasmonic acid response through the down-regulation of OsWRKY4 protein level in rice.