Review on Hormonal Regulation of Drought Stress Response in Plants

Drought stress is a major environmental challenge that significantly impairs plant growth, productivity, and survival. Plants have evolved complex physiological and biochemical mechanisms to perceive and respond to drought conditions, with plant hormones playing pivotal roles in mediating these responses. This abstract provides an overview of the key hormones involved in drought stress regulation—abscisic acid (ABA), jasmonic acid (JA), ethylene, cytokinins (CKs), and gibberellins (Gas)—and their interactions in orchestrating drought tolerance mechanisms. Abscisic acid (ABA) is the central hormone in drought stress signalling. It accumulates rapidly under water deficit conditions, triggering stomatal closure to reduce water loss and activating the expression of drought-responsive genes. ABA's role is mediated through a complex signalling cascade involving receptors (PYR/PYL/RCAR), protein phosphatases (PP2Cs), and kinases (SnRK2s), ultimately leading to transcriptional changes that enhance stress tolerance. Jasmonic acid (JA) and its derivatives contribute to drought tolerance by modulating antioxidant defence mechanisms and osmotic adjustments. JA signalling interacts with ABA pathways to fine-tune stress responses, often enhancing ABA's effects on stomatal closure and gene expression. Ethylene, a gaseous hormone, exhibits dual roles in drought stress. While high levels of ethylene can promote leaf senescence and abscission, contributing to water conservation, it also interacts with ABA signalling to regulate stomatal closure and root growth, optimizing water uptake and minimizing loss. Cytokinins (CKs) generally promote cell division and growth, but under drought conditions, their levels decrease, which can lead to reduced shoot growth and enhanced root growth. This shift in resource allocation favours water uptake overgrowth, aiding plant survival during drought. CKs also interact with ABA, often antagonistically, to balance growth and stress responses. Gibberellins (Gas), known for promoting growth, are typically downregulated during drought stress to conserve energy and resources. The suppression of GA biosynthesis and signalling is crucial for maintaining growth arrest, a common drought avoidance strategy. In summary, the hormonal regulation of drought stress response in plants is a highly intricate and dynamic process involving multiple hormones and their interactions. Understanding these regulatory networks is essential for developing strategies to enhance drought tolerance in crops, thereby ensuring agricultural productivity in the face of increasing water scarcity.