FIGURE 1.

Shared responses of plant roots to abiotic stresses. Roots display different cellular and molecular responses to alleviate the negative effects in their development and functionality provoked by abiotic stresses. Several key sensing, signaling and regulatory networks are shared between different stresses. First, roots are able to sense the stress and activate several physiological adaptive processes. Many abiotic stresses provoke a damage of the membranes and the loss of ionic and osmotic homeostasis that triggers ROS (O₂^–, H₂O₂) accumulation within different organelles. ROS is produced at the plasma membrane or the mitochondria by NADPH oxidases (RBOHs). This ROS has a dual function in response to abiotic stresses. Although at high levels, ROS are toxic to the cells, they can also act as a signal transducer activating Ca²⁺ channels that causes an increase in the intracellular Ca²⁺ concentration. This flux of Ca²⁺ triggers a cascade of events that activates calcium-dependent protein kinases (MAPKs) that phosphorylate and activate different TFs in the nucleus. These TFs belong to different families including, DREBs, MYBs, NAC, ERFs, WRKY, and HSFs. These TFs can regulate the expression of downstream genes involved in specific gene regulatory networks modulating each abiotic stress. They also regulate the biosynthesis and the metabolism of different phytohormones that in turn coordinate various signal transduction pathways regulating abiotic-stress response. On the other hand, interplay between ROS and hormone signaling orchestrates the acclimation response of plants to different abiotic stress combinations.