Phosphorylation dynamics in a flg22-induced, heterotrimeric G-protein dependent signaling network in Arabidopsis thaliana reveals a candidate PP2A phosphatase involved in AtRGS1 trafficking

Abstract

flg22 is recognized by the plant cell as a signal indicating that bacteria are present. Here we show a rapid and massive change in protein abundance and phosphorylation state of the Arabidopsis root cell proteome in wildtype and a mutant deficient in G-protein coupled signaling. Many of the flg22-induced changes fall on proteins comprising the G protein interactome and on highly populated hubs of the immunity network. Approximately 95% of the phosphorylation changes in the G-protein interactome depend on a functional G protein complex; some on proteins in the G protein interactome. One of these is ATB?, an interactor to REGULATOR OF G SIGNALING 1 protein (AtRGS1), a 7-transmembrane spanning modulator of the nucleotide-binding state of the core G protein complex. A null mutation of ATB? confers basal endocytosis of AtRGS1. AtRGS1 level is lower in the atb? mutant in a proteasome-dependent manner. We propose that phosphorylation-dependent endocytosis of AtRGS1 is part of the mechanism to degrade AtRGS1 thus sustaining activation of the G protein complex required for regulation of system dynamics in innate immunity.