5.4 ROS signaling
ROS scavenging and signaling play a key role in plant responses to both biotic and abiotic stress conditions (Pastori & Foyer, 2002; Fujita et al., 2006; Ton et al., 2009; Atkinson & Urwin, 2012; Kissoudis et al., 2014; Morales et al., 2016). During abiotic stress conditions, such as osmotic stress and high light, elevated levels of ROS must be detoxified by the plant to prevent damage to cell membranes and degradation of proteins, including important protein complexes related to photosynthesis (Staehelin & van der Staay, 1996; Wu et al., 2013; van Eerden et al., 2015; Kobayashi, 2016). Detoxification occurs through the action of antioxidants, including superoxide dismutase (SOD), enzymes and metabolites from the ascorbate‑glutathione cycle, and catalase (CAT) (see de Carvalho et al., 2013 for review). During biotic stress conditions, plants generate ROS to limit pathogen spread by initiating the hypersensitive response and cell death (Atkinson & Urwin, 2012). In both cases, ROS serve as a signal of stress conditions and elicit downstream ROS-responsive genes. This includes transcription factors, ABA biosynthetic genes, and antioxidant metabolism genes (Atkinson & Urwin, 2012). Additionally, many biotic and abiotic stresses activate ROS production through NADPH oxidase (RBOH) proteins. RBOH proteins are regulated through several post-translational mechanisms by both biotic (aphid, bacterial, fungal infection) and abiotic stresses (salinity, heat, high light), making them a central hub for integrating multiple stress conditions (Rivero et al., 2022). Therefore, master regulators of ROS signaling mechanisms would be key targets for future research.