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

Plant J. 2011 Sep;67(5):840-51. doi: 10.1111/j.1365-313X.2011.04638.x. Epub 2011 Jun 24.


Currently, 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 γ-subunit (AGG3) that modulates morphological development and ABA-regulation of stomatal aperture. AGG3 strongly interacts with the Arabidopsis G-protein β-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 γ-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 γ-subunits) and the presence of a C-terminal Cys-rich domain. AGG3 thus represent a novel class of G-protein γ-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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Abscisic Acid / metabolism*
  • Amino Acid Sequence
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • DNA, Complementary / genetics
  • Flowers / growth & development
  • GTP-Binding Protein beta Subunits / genetics
  • GTP-Binding Protein beta Subunits / metabolism*
  • GTP-Binding Protein gamma Subunits / genetics
  • GTP-Binding Protein gamma Subunits / metabolism*
  • Germination
  • Hypocotyl / growth & development
  • Molecular Sequence Data
  • Mutagenesis, Insertional
  • Phenotype
  • Plant Leaves / growth & development
  • Plant Stomata / physiology
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / growth & development
  • Plants, Genetically Modified / physiology
  • Potassium Channels / metabolism*
  • Protein Interaction Mapping
  • RNA / genetics
  • Recombinant Fusion Proteins
  • Seeds / genetics
  • Seeds / growth & development
  • Seeds / physiology
  • Sequence Alignment
  • Signal Transduction


  • AGB1 protein, Arabidopsis
  • AGG3 protein, Arabidopsis
  • Arabidopsis Proteins
  • DNA, Complementary
  • GTP-Binding Protein beta Subunits
  • GTP-Binding Protein gamma Subunits
  • Potassium Channels
  • Recombinant Fusion Proteins
  • RNA
  • Abscisic Acid