Role of phytohormones in regulating cold stress tolerance: Physiological and molecular approaches for developing cold-smart crop plants

Global climate variations induce extreme temperatures and significantly decrease crop production, leading to food insecurity worldwide. Temperature extremes (mainly cold stress (CS): chilling 0–15 °C and freezing <0 °C temperatures) limit plant growth and development and severely affect plant physiology and biochemical and molecular processes. Subsequently, plants execute numerous endogenous mechanisms, including phytohormone biosynthesis (i.e., abscisic acid, cytokinins, jasmonic acid, salicylic acid, gibberellic acid, brassinosteroids, indole-3-acetic acid, ethylene, and strigolactones) to tolerate stressful environments. Phytohormones are vital for managing diverse events associated with plant growth and development under CS as important endogenous signaling substances that dynamically arbitrate many physiological, biochemical, and molecular responses through a stress-responsive regulatory cascade. This review briefly appraises plant responses and adaptation mechanisms to CS and then comprehensively reports on the crucial role of several phytohormones in adjusting the CS response for plant acclimation. We also discuss phytohormone-regulated genes controlling CS tolerance and their genetic engineering to combat CS in diverse plant species and develop future CS-smart crop plants. The potential of state-of-the-art omics approaches to help identify phytohormone-induced novel genes, metabolites, and metabolic pathways is also discussed. In short, we conclude that the exogenous application of phytohormones and genetic engineering of phytohormones-regulated genes are promising techniques for developing cold-smart crop plants.