G Protein-Coupled Receptor Signaling in Plants

Abstract

Plants, like other multicellular organisms, rely on signal transduction for cell–cell commu- nication and responses to the environment. One prominent mechanism for signaling is the use of small GTPases as on/off switches. In plants, heterotrimeric G proteins, consisting of an alpha, beta, and gamma subunits, and Rop GTPases, which are Rho-related proteins in plants, play a role in a myriad of developmental, hormonal, and environmental responses. In addition, Rab-GTPases regulate intracellular traffi cking. This book describes methods used in the study of small GTPases and related proteins. In eukaryotes, heterotrimeric G proteins are associated with G protein-coupled recep- tors (GPCRs). Remarkably, while GPCRs are highly prevalent in animals and yeast, very few candidate GPCRs have been identifi ed in plants. One major issue is that GPCRs are not well conserved in sequence. The chapter by Gookin and Bendtsen (Chapter 1 ) seeks to address this by using bioinformatics approaches to identify proteins matching GPCR char- acteristics. There is also a comparative dearth in the number of heterotrimeric G protein subunits present in plant genomes. Despite this, heterotrimeric G proteins play roles in several key plant processes, including several described in this book. In contrast, there are several dozen Rab-GTPases present in plants, the function of each of which is just begin- ning to be understood. Finally, most G proteins are subject to lipid modifi cation, which serves to facilitate membrane association and to promote protein–protein interactions. Heterotrimeric G pro- tein alpha and gamma subunits, Rop-GTPases, and Rab-GTPases are all subject to the addition to one or more lipid moieties. Several chapters cover how to identify these lipid modifi cations, which include myristoylation, acylation, and prenylation. Further studies into the roles of small GTPases will help elucidate several key processes in plants.