Plant signaling networks involving reactive oxygen species and Ca²⁺

Although reactive oxygen species (ROS) are highly toxic substances and are produced during aerobic respiration and photosynthesis, recent studies have demonstrated that ROS, such as superoxide anion (O²-) and hydrogen peroxide (H₂O₂), are deliberately produced as important signaling messengers playing key roles in regulating a broad range of physiological processes including cellular growth and development as well as adaptation to environmental changes in plants. Given the toxicity of ROS, the enzymatic ROS production needs to be tightly regulated both spatially and temporally. Respiratory burst oxidase homologues (Rboh) have been identified as ROS-producing NADPH oxidases, which act as key signaling nodes integrating multiple signal transduction pathways in plants. We here discuss the interrelationship among signaling pathways involving Ca²⁺, protein phosphorylation and Rboh-mediated ROS production, as well as physiological roles of the signaling networks.