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

Plant heterotrimeric G proteins transduce extracellular signals that activate plant immunity. Plants encode canonical and non-canonical G and G{gamma} subunits, but only a single canonical G{beta} subunit is known. The existence of only one G{beta} subunit limits the number of heterotrimeric G protein combinations able to transduce different signals. It remains unknown whether non-canonical G{beta} subunits exist. Here, we identify two WD40-repeat genes that negatively regulate plant immunity. The proteins encoded by these two genes, DEFENSE REGULATED WD40-REPEAT 1 and 2 (DRW1/2), are structurally similar to AGB1. DRW2 localizes to the plasma membrane and interacts with the canonical G and G{gamma} subunits. Reduced levels of DRW in the drw1 and drw2 single mutants resulted in greater MAPK activation in response to flagellin treatment and conferred increased resistance to the bacterial pathogen Pseudomonas syringae. Furthermore, the drw1 drw2 double-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 G{beta} subunits are not conserved with the canonical G{beta} subunit. Our study identifies additional heterotrimeric G protein components, greatly increasing the number of heterotrimeric G protein complexes that participate in signal transduction.