Reactive oxygen species and oxidative signalling in plants

Plants mastered the art of reduction/oxidation (redox) control early in evolution, incorporating reactive oxygen species (ROS) as ubiquitous 'pioneer' signalling molecules that mediate growth and stress responses. Each compartment of the plant cell generates ROS, particularly superoxide and hydrogen peroxide. By virtue of their photosynthetic metabolism, plants produce large quantities of hydrogen peroxide, particularly through the process of photorespiration, but they maintain low levels of oxidant accumulation in the absence of environmental or metabolic perturbations. ROS production and signalling are intimately associated with plant biology, such as growth and development, stress resistance, and immune responses. The chemical reactivity of ROS makes them excellent local and systemic signalling molecules. ROS produced by the respiratory burst oxidase homologues are particularly important in the long-distance cell-to-cell signalling process called the ROS wave. Interactions with cell proteins, particularly ROS receptors, such as the receptor kinase called H2O2-induced Ca2+ increases 1, serve to modulate the network of metabolic and hormonal pathways that underpin regulation and functions. ROS-dependent post-translational modifications of protein Cys residues are a central mechanism for the transmission of redox signals. In addition, ROS promote liquid-liquid phase separation that alters the location and function of proteins such as transcription factors, facilitating the formation of heterotypic transcriptional condensates that alter gene expression. ROS-dependent phase separation is a key mechanism for plants to adapt to environmental changes.