PLANT BIOLOGY Reciprocal Regulators: PLD and Gα

Unlike animals, plants have a limited repertoire of G proteins; for example, Arabidopsis has a single gene encoding a Gα subunit. Despite this low amount of diversity, plant G proteins are implicated in several plant pathways, including germination pathways, guard-cell signaling, and cell-cycle regulation. Plants with mutations in either the gene encoding phospholipase D (PLD) or Gα exhibit some similar phenotypes. Zhao and Wang investigated the biochemical interaction between PLD and Gα, specifically PLDα1 and Gα from Arabidopsis. A direct interaction was detected using recombinant proteins in glutathione S-transferase pull-down experiments and with recombinant Gα and leaf extracts. Furthermore, this interaction was dependent on a DRY motif in PLD, which is also present in many animal G protein-coupled receptors. Biochemical activity assays with the Gα bound to various guanosine triphosphate (GTP) analogs indicated that the guanosine diphosphate-bound Gα interacted most strongly with PLD and inhibited PLD activity; whereas GTP binding appeared to decrease this interaction. PLD stimulated the guanosine triphosphatase activity of Gα. Thus, there is the possibility of a cycle of activation and deactivation occurring as the two proteins interact. The nature of how this interaction regulates plant signaling awaits further analysis.

J. Zhao, X. Wang, Arabidopsis phospholipase Dα1 interacts with the heterotrimeric G-protein α-subunit through a motif analogous to the DRY motif in G-protein-coupled receptors. J. Biol. Chem. 279, 1794-1800 (2004). [Abstract] [Full Text]