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]