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bioRxiv · 10.1101/2025.09.10.672744

UDP-glucose Activation of a G-protein/Sucrose Synthase Signaling Supercomplex

Jia, H.·Lou, F.·Watkins, J.·Oliveira, C. C.·Tate, C. G.·Jones, A. M.
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Abstract

Arabidopsis thaliana REGULATOR OF G PROTEIN SIGNALING 1 (AtRGS1, hereafter, RGS1) within the heterotrimeric G protein complex plays a role in sensing extracellular signals. High millimolar concentrations of some sugars induce RGS1 endocytosis and therefore G protein activation. However, this is not likely a direct, rather an indirect effect through a sugar metabolite. One metabolite at the plasma membrane where RGS1 resides is UDP-glucose (UDPG) produced by SUCROSE SYNTHASE (SUS) enzymes, previously shown to interact with RGS1. Our direct measurements indicate that the Kd for UDPG binding to RGS1 (2.4 {micro}M) is consistent with UDPG activation of RGS1 with an EC50 of 17 {micro}M to rapidly trigger G protein activation within minutes. RGS1 associates directly with SUS1 and SUS4, exhibiting affinities (Kd = 161 nM and 106 nM, respectively) that are markedly tighter than the corresponding Km values for UDPG formation (40 {micro}M and 70 {micro}M, respectively). Therefore, SUS may be one source for this RGS1 ligand in a manner analogous to "metabolite funneling" in enzymology. UDPG induces rapid phosphorylation of RGS1 at the C-terminal phosphorylation cluster, a site previously implicated in RGS1 endocytosis and G protein activation. UDPG activation of RGS1 changes the global transcript profiles in various processes, largely involving plant defense. These results provide the first molecular evidence for UDPG as a newly recognized low-molecular weight signal controlling key aspects of plant physiology.

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Jia, H., Lou, F., Watkins, J., Oliveira, C. C., Tate, C. G., Jones, A. M.. 2025-09-12. UDP-glucose Activation of a G-protein/Sucrose Synthase Signaling Supercomplex. https://doi.org/10.1101/2025.09.10.672744

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