Biased Signaling: Distinct Ligand-directed Plasma Membrane Signalosomes Using a Common RGS/G protein Core

Abstract

Abbreviations: Arabidopsis thaliana Regulator of G Signaling (AtRGS1), Clathrin-Mediated 43 Endocytosis (CME), Sterol-Dependent Endocytosis (SDE), Total Internal Reflection 44 Fluorescence Microscopy (TIRF), Clathrin Light Chain (CLC), Flotilin 1 (FLOT1), 45 Vacuolar Protein Sorting 26 (VPS26) 46 SUMMARY 47 Biased signaling occurs when different ligands that are directed at the same receptor launch 48 different cellular outcomes. Because of their pharmacological importance, we know the most 49 about biased ligands and little is known about other mechanisms to achieve signaling bias. 50 In the canonical animal G protein system, endocytosis of a 7-transmembrane GPCR 51 desensitizes a cell from its extracellular signal. β-arrestins facilitate GPCR endocytosis but 52 also propagate cytoplasmic signaling depending on the bias. In Arabidopsis, GPCRs are not 53 required for G protein coupled signaling because the heterotrimeric G protein complex 54 spontaneously exchanges nucleotide. Instead, the prototype 7-transmembrane Regulator of 55 G Signaling 1 protein AtRGS1 modulates G signaling and through ligand-dependent 56 endocytosis, de-repression of signaling is initiated but canonical arrestins are not involved. 57 Endocytosis initiates from two separate pools of plasma membrane: microdomains and a 58 clathrin-accessible neighborhood, each with a select set of discriminators, activators, and 59 newly-discovered arrestin-like adaptors. Different trafficking origins and trajectories lead 60 to different cellular outcomes. Thus, compartmentation with its attendant signalosome 61

Heterotrimeric G protein signalling in plant biotic and abiotic stress response

“…These studies indicate that the MAPK cascade could act as a downstream effector of G protein signalling (Lieberherr et al 2005; Su et al 2015). Interestingly, recent studies found flg22 initiates AtRGS1 endocytosis via clathrin‐mediated endocytosis (CME) to induce a MAPK cascade known to drive transcriptional reprogramming (Ross‐Elliott et al 2020). Whereas glucose induces endocytosis of AtRGS1 via sterol‐dependent endocytosis (SDE) to induce genes transcriptional change independent of the MAPK cascade (Ross‐Elliott et al 2020).…”

“…Interestingly, recent studies found flg22 initiates AtRGS1 endocytosis via clathrin‐mediated endocytosis (CME) to induce a MAPK cascade known to drive transcriptional reprogramming (Ross‐Elliott et al 2020). Whereas glucose induces endocytosis of AtRGS1 via sterol‐dependent endocytosis (SDE) to induce genes transcriptional change independent of the MAPK cascade (Ross‐Elliott et al 2020). Although MAPK activation is recognized as a defence marker in plant immunity, how G protein complex triggers activation of the MAPK cascade still needs further exploration (Su et al 2015).…”