Minisymposium 2: Signaling

Abs # 12001: Role of a Seven-transmembrane RGS Protein in Sugar Signaling in Arabidopsis

Presenter:	Jones, Alan M, alan_jones@unc.edu
Authors	Jones, Alan M (A) (B)
Affiliations:	(A): University of North Carolina, Dept of Biology (B): Dept. of Pharmacology

Arabidopsis contains a single Regulator of G-protein Signaling (AtRGS1) protein. RGS proteins act to desensitize signaling pathways involving heterotrimeric G proteins by accelerating the intrinsic GTPase activity of the alpha subunit. AtRGS1 is unusual because it contains a seven-transmembrane (7TM) domain at its amino-terminal half and a functional RGS box at its cytosolic-facing, C-terminal half (Chen, et al Science 301: 1728-1731, 2003). D-glucose serves as both a metabolite and a hormone-like signal that regulates plant cell proliferation. A high D-glucose concentration arrests cell proliferation, but Arabidopsis mutants lacking AtRGS1 are insensitive to high concentrations of D-glucose and sucrose, but have the same sensitivity to other hexose sugars and dissacharides. Conversely, plants ectopically expressing AtRGS1 are hypersensitive to sugars. D-glucose, but not L-glucose, causes rapid internalization of a AtRGS1:GFP fusion protein in hypocotyl epidermal and root cortical cells which is reminiscent of the behavior of some animal 7TM receptors. Stability of AtRGS1 in certain cell types is dependent on a protein designated AtGIP1 which was identified as an interactor to the single canonical heterotrimeric G protein alpha subunit. atgip1-1 null mutants are hypersensitive to D-glucose and has many other phenotypes. Many of the phenotypes of atgip1-1 are found in the atgip1-1,atgpa1-3 double mutants indicating that atgip1-1 is epistatic to atgpa1-3 and suggesting that GIP1 acts downstream of GPA1. Stability of the alpha subunit is also dependent on GIP1. GIP1 serves to desensitize cells to glucose by controlling the steady-state levels of AtRGS1 protein. These results raise the possibility that AtRGS1 is a glucose receptor that controls cell proliferation through regulation of the active state of its cognate G-protein complex.