title: Membrane-localized extra-large G proteins and Gbg of the heterotrimeric G proteins form functional complexes engaged in plant immunity in Arabidopsis.
abstract: In animals, heterotrimeric G proteins, comprising Ga, Gb, and Gg subunits, are molecular switches whose function tightly depends on Ga and Gbg interaction. Intriguingly, in Arabidopsis (Arabidopsis thaliana), multiple defense responses involve Gbg, but not Ga. We report here that the Gbg dimer directly partners with extra-large G proteins (XLGs) to mediate plant immunity. Arabidopsis mutants deficient in XLGs, Gb, and Gg are similarly compromised in several pathogen defense responses, including disease development and production of reactive oxygen species. Genetic analysis of double, triple, and quadruple mutants confirmed that XLGs and Gbg functionally interact in the same defense signaling pathways. In addition, mutations in XLG2 suppressed the seedling lethal and cell death phenotypes of BRASSINOSTEROID INSENSITIVE1-associated receptor kinase1-interacting receptor-like kinase1 mutants in an identical way as reported for Arabidopsis Gb-deficient mutants. Yeast (Saccharomyces cerevisiae) three-hybrid and bimolecular fluorescent complementation assays revealed that XLG2 physically interacts with all three possible Gbg dimers at the plasma membrane. Phylogenetic analysis indicated a close relationship between XLGs and plant Ga subunits, placing the divergence point at the dawn of land plant evolution. Based on these findings, we conclude that XLGs form functional complexes with Gbg dimers, although the mechanism of action of these complexes, including activation/deactivation, must be radically different form the one used by the canonical Ga subunit and are not likely to share the same receptors. Accordingly, XLGs expand the repertoire of heterotrimeric G proteins in plants and reveal a higher level of diversity in heterotrimeric G protein signaling.
authors.forename: Natsumi
authors.initials: N
authors.lastname: Maruta
authors.forename: Yuri
authors.initials: Y
authors.lastname: Trusov
authors.forename: Eric
authors.initials: E
authors.lastname: Brenya
authors.forename: Urvi
authors.initials: U
authors.lastname: Parekh
authors.forename: José Ramón
authors.initials: JR
authors.lastname: Botella
mesh_terms: D017360:Arabidopsis / Q000276:immunology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D016923:Cell Death; D002462:Cell Membrane / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D044388:GTP-Binding Protein gamma Subunits / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D000069452:Pathogen-Associated Molecular Pattern Molecules / Q000378:metabolism; D010802:Phylogeny; D057865:Plant Immunity; D011485:Protein Binding; D055503:Protein Multimerization; D016897:Respiratory Burst; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D015398:Signal Transduction; D013045:Species Specificity; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D046912:Multiprotein Complexes; D000069452:Pathogen-Associated Molecular Pattern Molecules; D020962:Heterotrimeric GTP-Binding Proteins