Heterotrimeric G-proteins in plant cell signaling

Heterotrimeric G-proteins, which couple cell surface receptors with interna l effecters, are evident in all eukaryotes. Their operation involves recept or activation, GTP/GDP exchange and modulation of effector activity; deacti vation occurs by an intrinsic GTPase activity. Structurally, G-proteins com prise three dissimilar subunits; G alpha, G beta and G gamma. The G alpha s ubunit consists of an alpha -helical and a GTPase domain, the latter is res ponsible for interaction with G beta gamma, receptor and effector. CP and G y form a tightly associated heterodimer which can also modulate effector ac tivity when released by the activated G alpha. Genome sequence and other da ta suggest that, in plants, there are several (similar to8-10?) G alpha, on e or two G beta and one G gamma. These proteins are expressed throughout th e plant, mainly in the plasma membrane and endoplasmic reticulum. In vivo, there is strong evidence for G-protein control of ion channels, particularl y K+, in the response pathways to fungal and bacterial pathogens as well as in some aspects of gibberellin, abscisic acid and auxin signaling pathways . Finally, future prospects for understanding plant G-protein linked signal ing will rely on new and emerging technologies; these include antisense sup pression, gene knockouts, yeast two-hybrid and phage display molecular appr oaches, intracellular immunization using recombinant single chain antibodie s and expression of peptide encoding minigenes. (C) New Phytologist (2001) 151: 165-174.