Reactive oxygen species (ROS) are important messengers in eukaryotic organisms. Extracellular ROS production by NADPH oxidases in plants is triggered by receptor-like protein kinase (RLK)-dependent signaling networks. This ROS production is tightly controlled by multiple mechanisms including phosphorylation by different kinases. Here we show that the cysteine-rich RLK CRK2 exists in a preformed complex with the NADPH oxidase RBOHD at the plasma membrane. 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. We identified phosphorylation sites in the C-terminal region of RBOHD and mutations of the phosphorylation sites modulate ROS production in response to biotic stimuli. Our work demonstrates that CRK2 occupies a central role in controlling ROS production and highlights that regulation of NADPH oxidase activity by phosphorylation of the C-terminal region is an ancient mechanism which is conserved between animals and plants.