Heterotrimeric G-Protein-Dependent Proteome and Phosphoproteome in Unstimulated Arabidopsis Roots

Abstract

The G-protein complex is a cytoplasmic on-off molecular switch that is set by plasma membrane receptors that activate upon binding of its cognate extracellular agonist. In animals, the default setting is the “off” resting state, while in plants, the default state is constitutively “on” but repressed by a plasma membrane receptor-like protein. De-repression appears to involve specific phosphorylation of key elements of the G-protein complex and possibly target proteins that are positioned downstream of this complex. To address this possibility, we quantified protein abundance and phosphorylation state in wild type and G-protein deficient Arabidopsis roots in the unstimulated resting state. A total of 3,246 phosphorylated and 8,141 non-modified protein groups were identified. We found that 428 phosphorylation sites decreased and 509 sites increased in abundance in the G-protein quadrupole mutant lacking an operable G-protein-complex. Kinases with known roles in G-protein signaling including MAP KINASE 6 and FERONIA were differentially phosphorylated along with many other proteins now implicated in the control of G-protein signaling. Taken together, these datasets will enable the discovery of novel proteins and biological processes dependent on G-protein signaling.