Extra-large G proteins and their roles in plant development and responses to environmental stresses

Eukaryotic G (guanine nucleotide-binding) proteins mediate important signal transduction pathways involved in diverse biological processes, including plant immunity against a wide range of pathogens. Plant signaling relies significantly on G proteins, including the Gα, Gβ, and Gγ subunits, which mediate important functions. Extra-large GTP-binding proteins (XLGs) are a subfamily of plant-specific Gα proteins that structurally resemble canonical Gα proteins but have distinct functional roles. Unlike canonical Gα proteins, XLGs lack intrinsic GTPase activity and possess an extended N-terminal region with nuclear localization signals, and interact with plasma membrane-localized receptors, suggesting their roles beyond plasma membrane signaling. XLGs play an essential role in a variety of physiological processes, such as root morphogenesis, chloroplast development, and responses to biotic and abiotic stressors. Among the XLGs, XLG1, XLG2, and XLG3 play especially vital roles with XLG2 and XLG3 involved in pathogen perception and signal transduction for activation of immune responses. XLGs interact with G-protein subunits and receptor-like kinases (RLKs), particularly FLS2 and BIK1, to form dynamic complexes involved in defense signal transduction. Several recent invesitgations demonstrate the significance of XLGs in modulating plant immunity and development suggesting their application for enhancing crop output and resilience. Understanding the mechanisms behind XLG functions may assistin the development of novel approaches to enhance plant resilience to environmental challenges. This review highlights the roles of XLG proteins in plant development and stress responses.