Calcium-dependent NADPH oxidase that generates superoxide. Involved in the generation of reactive oxygen species (ROS) during incompatible interactions with pathogens, in response to pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) signaling and in UV-B and abscisic acid ROS-dependent signaling and via SIK1 mediated activation by phosphorylation (PubMed:30212650). Might be required for ROS signal amplification during light stress. Inhibited by diphenylene iodinium (DPI). Monomer and homodimer (By similarity). Interacts with BIK1 and FLS2 (PubMed:24629339). Interacts with PBL13 (PubMed:26432875). Binds to SIK1 upon flagellin perception and becomes activated by phosphorylation (PubMed:30212650). More abundant in roots than in leaves, stems or inflorescences. Expressed in mesophyll and guard cells. Up-regulated by pathogen infection and by abscisic acid. Phosphorylated at Ser-39, Ser-343 and Ser-347 by BIK1 upon flagellin (flg22) treatment (PubMed:24629339). Activated by phosphorylation at Ser-347 mediated by SIK1 and at Ser-8, Ser-9 and Ser-339 upon flagellin (e.g. flg22) perception (PubMed:30212650). Plants do not accumulate reactive oxygen species during disease-resistance reactions, do not up-regulate UV-B-dependent gene expression and are impaired in abscisic acid-induced stomatal closing and in root growth and seed germination inhibitions. Belongs to the RBOH (TC 5.B.1.3) family.