Phosphorylation-Dependent Regulation of G-Protein Cycle during Nodule Formation in Soybean

Abstract

ORCID IDs: 0000-0002-6738-3574 (S.R.C.); 0000-0002-5570-3120 (S.P.)Signaling pathways mediated by heterotrimeric G-protein complexes comprising Ga, Gb, and Gg subunits and their regulatory RGS (Regulator of G-protein Signaling) protein are conserved in all eukaryotes. We have shown that the specific Gb and Gg proteins of a soybean (Glycine max) heterotrimeric G-protein complex are involved in regulation of nodulation. We now demonstrate the role of Nod factor receptor 1 (NFR1)-mediated phosphorylation in regulation of the G-protein cycle during nodulation in soybean. We also show that during nodulation, the G-protein cycle is regulated by the activity of RGS proteins. Lower or higher expression of RGS proteins results in fewer or more nodules, respectively. NFR1 interacts with RGS proteins and phosphorylates them. Analysis of phosphorylated RGS protein identifies specific amino acids that, when phosphorylated, result in significantly higher GTPase accelerating activity. These data point to phosphorylation-based regulation of G-protein signaling during nodule development. We propose that active NFR1 receptors phosphorylate and activate RGS proteins, which help maintain the Ga proteins in their inactive, trimeric conformation, resulting in successful nodule development. Alternatively, RGS proteins might also have a direct role in regulating nodulation because overexpression of their phospho-mimic version leads to partial restoration of nodule formation in nod49 mutants.

Gα and regulator of G‐protein signaling (RGS) protein pairs maintain functional compatibility and conserved interaction interfaces throughout evolution despite frequent loss of RGS proteins in plants

“…This might make RGS‐mediated fast signal termination unnecessary. However, the functional analysis of RGS in A. thaliana and soybean ( G. max ) supports its key roles during regulation of important physiological processes (Chen & Jones, ; Fan et al ., ; Roy Choudhury & Pandey, ). Another notion is that the G‐protein cycle in plants with an inherent RGS protein is regulated differently from the G‐protein cycle in plants lacking an RGS protein.…”

“…This might make RGS-mediated fast signal termination unnecessary. However, the functional analysis of RGS in A. thaliana and soybean (G. max) supports its key roles during regulation of important physiological processes (Chen & Jones, 2004;Fan et al, 2008;Roy Choudhury & Pandey, 2015 New Phytologist (2017)…”

Sporophyte formation and life cycle completion in moss requires heterotrimeric G-proteins

“…Genetic and physiological analysis of Arabidopsis, rice, soybean, and maize mutants suggests that G-proteins regulate a broad spectrum of signaling pathways in plants (Urano and Jones, 2014). The most obvious developmental defects exist in the Ga mutants of rice and maize (Ashikari et al, 1999;Bommert et al, 2013), which show severe dwarfism and alterations in inflorescence architecture, and in soybean where G-proteins regulate nodule formation (Roy Choudhury and Pandey, 2015). In Arabidopsis, where G-proteins have been characterized in most detail, changes in the overall plant development, morphology, and response to environment are observed due to the lack of one or more G-protein subunits; however, none of these impair the ability of the plant to complete its life cycle (Urano and Jones, 2014).…”

Dynamic and diverse sugar signaling

“…It will be a promising investigation to determine whether cell-wall invertases or sucrose transporters are required to generate high local sugar signals to stimulate RGS1 signaling [7]. A significant recent study has implicated a role of RGS1 in soybean nodulation [79*]. Distinct from RGS1 phosphorylation by WNKs to trigger endocytosis in Arabidopsis sugar signaling [77*], Nod factor receptor1 (NFR1) phosphorylates RGS1 to accelerate GTPase activity and maintains Gα proteins in inactive trimeric conformation.…”