Heterotrimeric G Proteins in Plants: Canonical and Atypical Gα Subunits

Heterotrimeric GTP-binding proteins (G proteins), consisting of G alpha, G beta and G gamma subunits, transduce signals from a diverse range of extracellular stimuli, resulting in the regulation of numerous cellular and physiological functions in Eukaryotes. According to the classic G protein paradigm established in animal models, the bound guanine nucleotide on a G alpha subunit, either guanosine diphosphate (GDP) or guanosine triphosphate (GTP) determines the inactive or active mode, respectively. In plants, there are two types of G alpha subunits: canonical G alpha subunits structurally similar to their animal counterparts and unconventional extra-large G alpha subunits (XLGs) containing a C-terminal domain homologous to the canonical G alpha along with an extended N-terminal domain. Both G alpha and XLG subunits interact with G beta gamma dimers and regulator of G protein signalling (RGS) protein. Plant G proteins are implicated directly or indirectly in developmental processes, stress responses, and innate immunity. It is established that despite the substantial overall similarity between plant and animal G alpha subunits, they convey signalling differently including the mechanism by which they are activated. This review emphasizes the unique characteristics of plant G alpha subunits and speculates on their unique signalling mechanisms.

Automated summary

Plant G proteins consist of canonical G alpha subunits and unconventional XLG subunits, interacting with G beta gamma dimers and RGS protein, and participating in development, stress responses, and immunity. Despite the overall similarity between plant and animal G alpha subunits, they convey signals differently.