The genome of Arabidopsis thaliana appears to contain one set of genes that code for the three subunits in the heterotrimeric G protein complex: Gα (coded by AtGPA1), Gβ, and Gγ. These G proteins are found in nearly all parts of the developing plant (roots, leaves, reproductive organs) and are associated with the plasma membrane, and endoplasmic reticulum. Okamoto et al. have identified Gα as an important regulator of hypocotyl elongation. By using transgenic plants that conditionally overexpress Gα (as directed by a glucocorticoid-sensitive promoter), Okamoto et al. found greater inhibition of hypocotyl elongation in transgenic plants overexpressing a constitutively active form of Gα, than in plants overexpressing the wild-type Gα. Thus, Gα activity appears to influence attenuating hypocotyl cell elongation. These responses occurred in far-red (phytochrome A-dependent) and red light (phytochrome B-dependent) conditions, and the authors also observed that another component of the phytochrome A signaling pathway, called FHY1, was essential for mediating the Gα effect on hypocotyl elongation.
H. Okamoto, M. Matsui, X. W. Deng, Overexpression of the heterotrimeric G-protein α-subunit enhances phytochrome-mediated inhibition of hypocotyl elongation in Arabidopsis. Plant Cell 13, 1639-1652 (2001). [Abstract] [Full Text]