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

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