Abstract
The rice dwarf1 mutant is deficient in the α subunit of heterotrimeric G protein (Gα). To elucidate physiological roles of the heterotrimeric G protein in phythchrome signal transduction, we examined transcript levels of the typical light-inducible genes, namely LHCB and RBCS, in the mutant under various light conditions. The mutant seedlings exhibited reduced light-inducibility in these genes under the conditions trigger very low fluence responses (VLFR). Comparable levels of spectrophotometrically active phytochromes could be detected in the mutant with those observed for wild type, suggesting that phytochrome A, major photoreceptor for VLFR, is normal in this mutant. In addition, recombinant rice seedlings expressing the constitutively active Gα protein (Q223L) displayed significantly higher expression levels of these genes under the conditions induce VLFR. These results indicate that the Gα acts as a positive regulator in phytochrome A-signaling pathways for the light-inducible gene expression in rice plants.
