title: Diversity of heterotrimeric G-protein γ subunits in plants.
abstract: BACKGROUND
  Heterotrimeric 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.
  
  
  RESULTS
  After 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.
  
  
  CONCLUSIONS
  Phylogenetic 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.
authors.affiliation: Plant Genetic Engineering Laboratory, School of Agriculture and Food Sciences, University of Queensland, Brisbane, Queensland, 4072, Australia.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Trusov
authors.forename: David
authors.initials: D
authors.lastname: Chakravorty
authors.forename: José Ramón
authors.initials: JR
authors.lastname: Botella
mesh_terms: D000595:Amino Acid Sequence; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010944:Plants / Q000145:classification / Q000378:metabolism*; D017368:Protein Prenylation; D017386:Sequence Homology, Amino Acid
chemical_list: D020962:Heterotrimeric GTP-Binding Proteins