Time-dependent, Glucose-regulated Arabidopsis Regulator of G-Protein Signaling 1 Network

Plants lack 7-transmembrane, G-protein coupled receptors (GPCRs) because the G alpha subunit of the heterotrimeric G protein complex is “self-activating” - meaning that it spontaneously exchanges bound GDP for GTP without the need of a GPCR. In lieu of GPCRs, most plants have a seven transmembrane receptor-like Regulator of G Signaling (RGS) protein, a component of the complex that keeps G signaling in its non-activated state. The addition of glucose physically uncouples AtRGS1 from the complex through specific endocytosis leaving the activated G protein at the plasma membrane. Here, the complement of proteins in the AtRGS1/G-protein complex over time from glucose-induced endocytosis was profiled by immunoprecipitation coupled to mass spectrometry (IP-MS). A total of 119 proteins in the AtRGS1 complex were identified. Several known interactors of the complex were identified, thus validating the approach, but the vast majority were not known previously. AtRGS1 protein interactions were dynamically modulated by D-glucose. In response to D-glucose, a diverse range of proteins became maximally associated with AtRGS1, whereas endosomal trafficking proteins were more distinctively associated with AtRGS1 following D-glucose treatment. Functional analyses are consistent with core proteins operating in response to stimulus and other metabolic pathways and thus provide an insight into spatiotemporal and mechanistic aspects of AtRGS1 regulation.