Diversity of heterotrimeric G-protein γ subunits in plants

Abstract

BackgroundHeterotrimeric G-proteins, consisting of three subunits Gα, Gβ and Gγ are present in most eukaryotes and mediate signaling in numerous biological processes. In plants, Gγ subunits were shown to provide functional selectivity to G-proteins. Three unconventional Gγ subunits were recently reported in Arabidopsis, rice and soybean but no structural analysis has been reported so far. Their relationship with conventional Gγ subunits and taxonomical distribution has not been yet demonstrated.ResultsAfter an extensive similarity search through plant genomes, transcriptomes and proteomes we assembled over 200 non-redundant proteins related to the known Gγ subunits. Structural analysis of these sequences revealed that most of them lack the obligatory C-terminal prenylation motif (CaaX). According to their C-terminal structures we classified the plant Gγ subunits into three distinct types. Type A consists of Gγ subunits with a putative prenylation motif. Type B subunits lack a prenylation motif and do not have any cysteine residues in the C-terminal region, while type C subunits contain an extended C-terminal domain highly enriched with cysteines. Comparative analysis of C-terminal domains of the proteins, intron-exon arrangement of the corresponding genes and phylogenetic studies suggested a common origin of all plant Gγ subunits.ConclusionPhylogenetic analyses suggest that types C and B most probably originated independently from type A ancestors. We speculate on a potential mechanism used by those Gγ subunits lacking isoprenylation motifs to anchor the Gβγ dimer to the plasma membrane and propose a new flexible nomenclature for plant Gγ subunits. Finally, in the light of our new classification, we give a word of caution about the interpretation of Gγ research in Arabidopsis and its generalization to other plant species.

Characterization of the Heterotrimeric G-Protein Complex and Its Regulator from the Green Alga Chara braunii Expands the Evolutionary Breadth of Plant G-Protein Signaling

“…C. braunii G-protein genes showed an overall nucleotide sequence similarity of 53.1%, 48.1%, and 44.2%/39.2% with Arabidopsis GPA1, AGB1, and AGG1/AGG2, respectively. No sequence homologs were identified for AtAGG3 genes in Chara species, which is not surprising, as sequence homologs of AtAGG3 are present only in higher plants (Chakravorty et al, 2011;Li et al, 2012;Trusov et al, 2012). Conceptually translated amino acid sequences of C. braunii Ga, Gb, and Gg homologs (named CbGa, CbGb, and CbGg, hereafter) exhibit 47.9%, 43.9%, and 18.8%/23.1% identity (66.1%, 58.4%, and 28.6%/41% similarity) with the corresponding Arabidopsis proteins.…”

Heterotrimeric G-proteins in green algae

“…Sequence-based homology searches have successfully identified G-protein genes in a variety of plants. 24 Nonetheless, it can be stated without doubt that G-protein signaling of photo-autotrophic organisms evolved early in the plant lineage, long before embryophytes conquered terrestrial habitats. Furthermore, the origin of heterotrimeric G-protein signaling can be dated before major innovations like the appearance of phragmoplasts, but after or concurrent with the appearance of multicellular, filamentous morphology.…”

Membrane-Localized Extra-Large G Proteins and Gβγ of the Heterotrimeric G Proteins Form Functional Complexes Engaged in Plant Immunity in Arabidopsis

“…These unconventional subunits will join the unconventional extra-large Gg subunits (Chakravorty et al, 2011;Trusov et al, 2012), the unconventional regulator of G protein signaling1 (RGS1) protein, which combines the seven transmembrane domain and the RGS activity Temple and Jones, 2007), the scarcity of G protein-coupled receptors (Urano et al, 2013;Urano and Jones, 2014), the selfactivation and slow GTPase activity of the canonical Ga Jones et al, 2011;Urano et al, 2012), and the independent plasma membrane targeting of Ga and Gbg (Adjobo-Hermans et al, 2006;Zeng et al, 2007).…”