Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems (By similarity). Binds GTP with specificity. Plays a role in the root morphogenesis by regulation of the cell proliferation. Ubiquitous. Strongly expressed in vascular tissues, root and shoot meristems and lateral root primordia. The helical domain (514-664) is required for self-activation. No visible phenotype. Dark-grown xlg1-1 xlg2-1 xlg3-1 triple mutant plants showed markedly increased primary root length compared with wild-type plants. Dark-grown roots of the xlg triple mutants also showed altered sensitivity to sugars, abscisic acid (ABA) hyposensitivity and ethylene hypersensitivity, whereas seed germination in xlg triple mutants was hypersensitive to osmotic stress and ABA (PubMed:17999646). Belongs to the G-alpha family. XLG subfamily. Truncated C-terminus.