Abstract
For the purpose of isolating brassinosteroid(BR)-induced genes of rice, we monitored the transcriptomic responce of brd1, a mutant that has a defective BR biosynthetic gene OsBR6ox, to BL treatment. Among the up-regulated genes, we present detailed analyses of OsBU3 and OsBU17, both encoding putative bHLH proteins.
Rice overexpressing OsBU3 (OsBU3:OX) showed severe bending of the lamina joint. In contrast, RNAi plants designed to repress both OsBU3 and its paralogues displayed erect leaves. In addition, OsBU3:OX plants were resistant to brassinazole, an inhibitor of BR biosynthesis, suggesting that OsBU3 is not involved in BR biosynthesis but BR signaling. Analysis of promoter-GUS plants demonstrated that OsBU3 is specifically expressed in the lamina joint. Further, OsBU3:OX plants showed large grain and reduced fertility.
In contrast, OsBU17:OX showed erect leaves but did not show dwarfism. OsBU17 may be mainly involved in bending of the lamina joint.
