Calcium-dependent NADPH oxidase that generates superoxide. Generates reactive oxygen species (ROS) during incompatible interactions with pathogens and is important in the regulation of the hypersensitive response (HR). Involved in abscisic acid-induced stomatal closing and in UV-B and abscisic acid ROS-dependent signaling. Inhibited by diphenylene iodonium (DPI). Monomer and homodimer (By similarity). Interacts (via N-terminus) with CIPK26 (PubMed:23335733). Interacts (via N-terminus) with SRC2 (PubMed:23872431). Expressed in roots, stems, seedlings, inflorescences, leaves and guard cells. Up-regulated by abscisic acid. Not glycosylated. Phosphorylated by CIPK26. Belongs to the RBOH (TC 5.B.1.3) family. Was originally called RBOHA. Intron retention.