Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems (Probable). May function in a signal transduction pathway required for normal growth and development of internodes, leaves, panicles and seeds (PubMed:10377457). Involved in gibberellin signal transduction (PubMed:10468600, PubMed:11027362). Involved in R gene-mediated disease resistance. Functions upstream of the small GTPase RAC1 in the early steps of signaling (PubMed:12237405). Involved in brassinosteroid (BR) response. May not be a signaling molecule in BRI1-mediated perception or transduction (PubMed:17117160, PubMed:19036785). Acts together with the E3 ubiquitin ligase TUD1 to mediate a BR signaling pathway that affects plant growth and development (PubMed:23526892). G proteins are composed of 3 units; alpha, beta and gamma. The alpha chain contains the guanine nucleotide binding site (PubMed:15078334). Interacts with COLD1 (PubMed:25728666). Interacts with TUD1 (PubMed:23526892). Highly expressed in young internodes. Expressed in the base of the stamen, pistil, lemma, and palea before flowering and in the pericarp of the ovary after fertilization. By infection with an avirulent race of rice blast fungus (M.grisea) and sphingolipid elicitors (PubMed:12237405). Down-regulated by a virulent race of rice blast fungus (M.grisea) (PubMed:12237405). Down-regulated by 24-epi-brassinolide (PubMed:17117160). The helical domain (69-189) is required for self-activation. Dwarf plants and small seeds (PubMed:10377457, PubMed:10468600). Short internodes, leaves and panicles (PubMed:10377457). Belongs to the G-alpha family. Extended N-terminus.