Abiotic stress: Interplay between ROS, hormones and MAPKs

Reactive oxygen species (ROS) are endogenously produced by several plant organelles and compartments, particularly those with high electron transport rates, such as chloroplasts, mitochondria and peroxisomes as metabolic by-products that act as cellular messengers and redox regulators of several plant biological processes. Excessive accumulation of ROS causes oxidative stress leading to protein denaturation, lipids peroxidation, and nucleotides degradation, which results in cellular damage and ultimately cell death. Functional approaches have provided evidence of the convergence of signaling pathways regulating plant responses to developmental cues and abiotic and biotic stress factors. They have highlighted the role of phytohormones and redox signaling, and identified key regulatory elements – molecular hubs – where multiple signaling cascades converge. The integration of multiple signals through these hubs allows the plant to fine-tune its response to particular conditions. In this regard, growing evidence shows that the generation of ROS is one of the most common plant responses to different stresses, representing a point at which various signaling pathways come together to modulate the plant response to environmental cues. Redox regulation of integral pathway proteins provides a rapid and simple mechanism for the regulation of plant development and defence pathways. MAPK pathways are common and versatile signaling components that lie downstream of second messengers and hormones, and play central roles in plant responses to various stresses. In this review, the complex nature of plant stress signaling network is discussed. An emphasis on different signaling players with a specific attention to ROS as the primary source of the signaling battery in plants is presented. The interaction between ROS and other signaling components, e.g., redox homeostasis, MAPKs, and plant hormones has also been assessed.