Revisiting the Critical Role of ROS and RNS in Plant Defense

Reactive oxygen/nitrogen species (ROS/RNS) have personated themselves as integral components of signal transduction processes regulating vital functions in plants exposed to climate extremes. As toxic by-products of aerobic metabolism, recent findings have confirmed that ROS/RNS biosynthesis/signaling are essential for advancing important cellular and metabolic processes in plants. Studies have suggested that the growth-promoting functions of ROS/RNS are mainly attributed to the differences in their production and subsequent scavenging, thereby triggering a plethora of physiological and programmed signaling pathways. The activated programmed signaling pathways under the influence of ROS/RNS signaling to regulate respiratory burst oxidase homologs (RBOH). The activated RBOH establishes Spatio-temporal coordination with other signaling molecules and phytohormones, thus controlling the plant stress response. This review describes the different ROS/RNS produced in separate subcellular compartments in plants and their underlying mechanisms. Being toxic, how these ROS/RNS function as signaling molecules/components to regulate plant immune response under stress conditions is also highlighted and discussed with some novel findings in recent years. Finally, the present work also deciphers how these ROS/RNS are subsequently integrated with phytohormones and other signaling components to modulate stress-responsive genes/transcription factors responsible for improving plants' growth and development.