A receptor-like kinase mediated phosphorylation of Gα protein affects signaling during nodulation
SUMMARYHeterotrimeric G-proteins, comprised of Gα, Gβ and Gγ subunits regulate signaling in eukaryotes. In metazoans, G-proteins are activated by GPCR-mediated GDP to GTP exchange on Gα; however, the role of receptors in regulating plant G-protein signaling remains equivocal. Mounting evidence points to the involvement of receptor-like kinases (RLKs) in regulating plant G-protein signaling pathways, but their mechanistic details remain limited. We have previously shown that during soybean nodulation, the nod factor receptor 1 (NFR1) interacts with G-protein components and indirectly controls signaling.We explored the direct regulation of G-protein signaling by RLKs using protein-protein interactions, receptor-mediated phosphorylation and the effects of such phosphorylations on soybean nodule formation.Results presented in this study demonstrate a direct, phosphorylation-based regulation of Gα by symbiosis receptor kinase (SymRK). SymRKs interact with and phosphorylate Gα at multiple residues, including two in its active site, which abolishes GTP binding. In addition, phospho-mimetic Gα fails to interact with Gβγ, potentially allowing for constitutive signaling by the freed Gβγ.These results uncover a novel mechanism of G-protein cycle regulation in plants where receptor-mediated phosphorylation of Gα not only affects its activity, but also influences the availability of its signaling partners, thereby exerting a two-pronged control on signaling.