Rice ERECT LEAF 1 acts in an alternative brassinosteroid signaling pathway independent of the receptor kinase OsBRI1.

ERECT LEAF 1 (ELF1) was previously identified as a component of brassinosteroid signaling in rice. A double mutant obtained by crossing elf1-1 (a null mutant of ELF1) with d61-1 (a leaky mutant of OsBRI1) showed a more severe phenotype than did the elf1-1 single mutant, resembling that of a severe brassinosteroid-deficient mutant. Microarray analysis showed that the gene expression profile of elf1-1 was distinct from that of d61-12 (a leaky mutant of OsBRI1 with a phenotype similar to that of elf1-1), and fewer than half of genes differentially expressed between the wild-type and elf1-1 showed similar differences in d61-12 relative to the wild-type. These results indicate that less than half of ELF1-regulated genes in rice seedlings are affected by OsBRI1, and suggest that ELF1 acts in a rice brassinosteroid signaling pathway different from that initiated by OsBRI1. Gene expression analysis showed that some stress response-related genes were induced in elf1-1 but not in d61-12, and 8 of 9 genes oppositely regulated in elf1-1 and d61-12 were significantly up- or down-regulated in both elf1-1 and jasmonic acid-treated wild-type. These results imply that ELF1 suppresses stress-induced signalling, and that jasmonic acid signaling is stimulated in elf1-1; therefore, ELF1 may be involved in the brassinosteroid-mediated suppression of jasmonic acid response in rice.