Abstract
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.