Discovery of novel Defense Regulated WD40-repeat proteins DRW1/2 and their roles in plant immunity

Abstract

ABSTRACTPlant heterotrimeric G proteins transduce extracellular signals that activate plant immunity. Plants encode canonical and non-canonical Gα and Gγ subunits, but only a single canonical Gβ subunit is known. The existence of only one Gβ subunit limits the number of heterotrimeric G protein combinations able to transduce different signals. It remains unknown whether non-canonical Gβ subunits exist. Here, we identify two WD40-repeat genes that negatively regulate plant immunity. The proteins encoded by these two genes,DEFENSE REGULATED WD40-REPEAT1 and 2 (DRW1/2), are structurally similar to AGB1. DRW2 localizes to the plasma membrane and interacts with the canonical Gα and Gγ subunits. Reduced levels ofDRWin thedrw1anddrw2single mutants resulted in greater MAPK activation in response to flagellin treatment and conferred increased resistance to the bacterial pathogenPseudomonas syringae. Furthermore, thedrw1 drw2double-mutant also displayed increased MAPK activation upon flagellin treatment and broad-spectrum resistance against bacterial and fungal pathogen infection. The function of DRW1 and DRW2 is opposite of AGB1, which promotes immune signaling, suggesting that the function of these potential non-canonical Gβ subunits are not conserved with the canonical Gβ subunit. Our study identifies additional heterotrimeric G protein components, greatly increasing the number of heterotrimeric G protein complexes that participate in signal transduction.