Overexpression of the heterotrimeric G-protein alpha-subunit enhances phytochrome-mediated inhibition of hypocotyl elongation in Arabidopsis

Plant heterotrimeric G-proteins have been implicated in a number of signali ng processes. However, most of these studies are based on biochemical or ph armacological approaches. To examine the role of heterotrimeric G-proteins in plant development, we generated transgenic Arabidopsis expressing the G alpha subunit of the heterotrimeric G-protein under the control of a glucoc orticoid-inducible promoter. With the conditional overexpression of either the wild type or a constitutively active version of Arabidopsis Gel, transg enic seedlings exhibited a hypersensitive response to light. This enhanced light sensitivity was more exaggerated in a relatively lower intensity of l ight and was observed in white light as well as far-red, red, and blue ligh t conditions. The enhanced responses in far-red and red light required func tional phytochrome A and phytochrome B, respectively. Furthermore, the resp onse to far-red light depended on functional FHY1 but not on FIN219 and FHY 3. This dependence on FHY1 indicates that the Arabidopsis Ga protein may ac t only on a discrete branch of the phytochrome A signaling pathway. Thus, o ur results support the involvement of a heterotrimeric G-protein in the lig ht regulation of Arabidopsis seedling development.