Abstract
We have already reported about the BR-induced rice gene BRASSINOSTEROID UPREGULATED1 (BU1), encoding a helixloop-helix protein. BU1 protein is a positive regulator of BR response which controls bending of the lamina joint in rice. BU1 mainly expresses in lamina joint, young panicle and panicle. Rice plants overexpressing BU1 (BU1:OX) showed enhanced bending of the lamina joint, increased grain size, and resistance to brassinazole, an inhibitor of BR biosynthesis. In contrast to BU1:OX, RNAi plants designed to repress both BU1 and its homologs displayed erect leaves, although RNAi plants designed to repress only BU1 did not display erect leaves. In this research, BU1 homologs named BU1-like (BUL) genes were characterized. Expression levels of BU1, BUL1 to 3 decrease by application of Brz. Above all, BUL1 decreases most to the level of 15% compared to the control plant. Addition of BL increased the expression level of BUL2 twice compared to the control, however, the expression levels of BUL1 and BUL3 were not increased. BUL1 expressed in young panicle and panicle as well as BU1 in WT plant. BUL2 mainly expressed in young panicle and BUL3 expressed in leaf. Transgenic plants that overexpress and repress BUL1 were generated and analyzed.
