Plant G-protein signaling cascade and host defense

The heterotrimeric guanine-nucleotide-binding proteins (G-proteins) play a crucial role in signal transduction and regulate plant responses against biotic and abiotic stresses. Necrotrophic pathogens trigger G alpha subunit and, in contrast, sometimes G beta gamma dimers. Beneficial microbes play a vital role in the activation of heterotrimeric G-proteins in plants against biotrophic and necrotrophic pathogens. The subunits of G-protein (alpha, beta, and gamma) are activated differentially against different kinds of pathogens which in turn regulates the entry of the pathogen in a plant cell. Defense mediated by G-proteins in plants imparts resistance against several pathogens. Activation of different G-protein subunits depends on the mode of nutrition of the pathogen. The current review discussed the role of the three subunits against various pathogens. It appeared to be specific in the individual host-pathogen system as well as the role of effectors in the induction of G-proteins. We also discussed the G-protein-mediated production of reactive oxygen species (ROS), including H2O2, activation of NADPH oxidases, hypersensitive response (HR), phospholipases, and ion channels in response to microorganisms.