Arabidopsis thaliana RGS1 is a novel "regulator of G-protein signaling" (AtRGS1) protein that consists of an N-terminal seven transmembrane domain characteristic of G-protein-coupled receptors and a C-terminal RGS box. AtRGS1 modulates plant cell proliferation. Atrgs1 mutants are insensitive to glucose and less sensitive to fructose and sucrose, suggesting that sugar signaling in Arabidopsis involves AtRGS1. In addition, sugar metabolism and phosphorylation by hexokinase (HXK) are not required for AtRGS1-mediated sugar signaling, suggesting that AtRGS1 functions in a HXK-independent glucose signaling pathway.