Direct Regulation of the NADPH Oxidase RBOHD by the PRR-Associated Kinase BIK1 during Plant Immunity

The rapid production of reactive oxygen species (ROS) burst is a conserved signaling output in immunity across kingdoms. In plants, perception of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors (PRRs) activates the NADPH oxidase RBOHD by hitherto unknown mechanisms. Here, we show that RBOHD exists in complex with the receptor kinases EFR and FLS2, which are the PRRs for bacterial EF-Tu and flagellin, respectively. The plasma-membrane-associated kinase BIK1, which is a direct substrate of the PRR complex, directly interacts with and phosphorylates RBOHD upon PAMP perception. BIK1 phosphorylates different residues than calcium-dependent protein kinases, and both PAMP-induced BIK1 activation and BIK1-mediated phosphorylation of RBOHD are calcium independent. Importantly, phosphorylation of these residues is critical for the PAMP-induced ROS burst and antibacterial immunity. Our study reveals a rapid regulatory mechanism of a plant RBOH, which occurs in parallel with and is essential for its paradigmatic calcium-based regulation. [Display omitted] •The plasma membrane Arabidopsis NADPH oxidase RBOHD is part of the PRR complex•RBOHD is directly phosphorylated by the kinase BIK1 in response to PAMP perception•BIK1 activation and BIK1-mediated RBOHD phosphorylation are calcium independent•BIK1-mediated phosphorylation of RBOHD is critical for its function in immunity Kadota et al. describe how microbes activate the plant NADPH oxidase RBOHD. They show that RBOHD is part of a pathogen recognition complex. Upon microbial perception, RBOHD is phosphorylated and activated by BIK1, leading to production of reactive oxygen species that are involved in downstream immune signaling.