CRK2-mediated control of ROS production by phosphorylation of the RBOHD C-terminus in Arabidopsis

Reactive oxygen species (ROS) are important messengers in eukaryotic organisms and their production is tightly controlled. Active extracellular ROS production by NADPH oxidases in plants is triggered by receptor-like protein kinase (RLK)-dependent signaling networks. Here we show that the cysteine-rich RLK CRK2 exists in a preformed complex with the NADPH oxidase RBOHD at the plasma membrane in Arabidopsis. Functional CRK2 is required for the full pathogen-induced ROS burst and consequently the crk2 mutant is impaired in defense against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. We identified phosphorylation sites in the C-terminal region of RBOHD and mutations of these phosphorylation sites alter ROS production in response to biotic stimuli. Our work demonstrates that CRK2 regulates elicitor-triggered ROS production. We propose that regulation of NADPH oxidase activity by phosphorylation of the C-terminal region is an ancient mechanism and phospho-sites are conserved throughout the plant lineage and between animals and plants.