Function of α subunit of heterotrimeric G protein in brassinosteroid response of rice plants

Abstract

The α subunit of heterotrimeric G-proteins (Gα) is involved in a broad range of aspects of the brassinosteroid (BR) response, such as the enhancement of lamina bending. However, it has been suggested from epistatic analysis of d1 and d61, which are mutants deficient for Gα and the BR receptor BRI1, that Gα and BRI1 may function via distinct pathways in many cases. In this study, we investigated further the genetic interaction between Gα and BRI1. We report the analysis of transformants of d1-1 and d1-1/d61-7 into which were introduced a constitutively active form of Gα, Q223L. The application of 24-epi-brassinolide (24-epiBL) to d1-1 expressing Q223L still resulted in elongation of the coleoptile and, in fact, it was enhanced over the wild-type plant (WT) level in a concentration dependent manner. In d1-1/d617 expressing Q223L, the seed size was enlarged over that of d61-7 due to activation of Gα. These results suggest that Q223L is able to augment the BR response in response to 24-epiBL and also that Q223L functions independently of BRI1 in the process of determining seed morphology, given that Q223L was functional in the BRI1-deficient mutant, d61-7.