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. Acts as a positive regulator in resistance to pathogen that triggers the salicylic acid (SA) pathway. Promotes the DNA binding activity of RTV1 specifically to promoter regions of FT and SOC1 in vivo leading to the activation of floral integrator genes. Interacts with GB1. Component of a G-protein complex at least composed of XLG2 and GB1. Interacts with RTV1. Ubiquitous. Strongly expressed in vascular tissues, root and shoot meristems and lateral root primordia. By bacterial pathogen P.syringae. The helical domain (492-627) is required for self-activation. No visible phenotype. Enhanced susceptibility to P.syringae. 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.