An atypical heterotrimeric G‐protein γ‐subunit is involved in guard cell K⁺‐channel regulation and morphological development in Arabidopsis thaliana

Abstract

SUMMARYCurrently, there are strong inconsistencies in our knowledge of plant heterotrimeric G-proteins that suggest the existence of additional members of the family. We have identified a new Arabidopsis G-protein c-subunit (AGG3) that modulates morphological development and ABA-regulation of stomatal aperture. AGG3 strongly interacts with the Arabidopsis G-protein b-subunit in vivo and in vitro. Most importantly, AGG3-deficient mutants account for all but one of the 'orphan' phenotypes previously unexplained by the two known c-subunits in Arabidopsis. AGG3 has unique characteristics never before observed in plant or animal systems, such as its size (more than twice that of canonical c-subunits) and the presence of a C-terminal Cys-rich domain. AGG3 thus represent a novel class of G-protein c-subunits, widely spread throughout the plant kingdom but not present in animals. Homologues of AGG3 in rice have been identified as important quantitative trait loci for grain size and yield, but due to the atypical nature of the proteins their identity as G-protein subunits was thus far unknown. Our work demonstrates a similar trend in seeds of Arabidopsis agg3 mutants, and implicates G-proteins in such a crucial agronomic trait. The discovery of this highly atypical subunit reinforces the emerging notion that plant and animal G-proteins have distinct as well as shared evolutionary pathways.

Dissecting Arabidopsis Gβ Signal Transduction on the Protein Surface

“…it is known that the AGB1/AGG3 dimer is an important modulator of reproductive organ shapes (Chakravorty et al, 2011;Li et al, 2012). We found that W109A and S129R fully rescued this reproductive phenotype, whereas the other two tested AGB1 mutants failed to restore the wild-type morphology (Fig.…”

Phosphorylation-Dependent Regulation of G-Protein Cycle during Nodule Formation in Soybean

“…Plants also possess relatively fewer G-protein subunits when compared with the mammalian systems (Chen et al, 2003;Perfus-Barbeoch et al, 2004;Chakravorty et al, 2011). The most elaborate plant G-protein network identified to date is present in soybean where recent genome duplication has led to existence of 4 Ga, 4 Gb, 12 Gg, and 2 RGS proteins Choudhury et al, 2011Choudhury et al, , 2012.…”

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.…”