Mechanistic Insights into Plant Drought Tolerance: A Multi-level Perspective

Drought stress (DS) is a major environmental factor impacting plant growth and productivity on a global scale. Due to rapidly changing climatic conditions, DS is proving to be the most detrimental among various stresses. It poses a significant threat to agricultural sustainability by hindering the growth and yield of agriculturally important crops worldwide. Plants have developed various adaptive mechanisms, including physio-biochemical changes, secondary metabolism, and genetic regulation, to cope with such challenging conditions. This review provides a comprehensive analysis of how DS influences physiological processes such as photosynthesis, and stomatal conductance, alongside biochemical adjustments. Furthermore, this review investigates the alterations in secondary metabolism, emphasizing the enhanced synthesis of phenolics, flavonoids, terpenoids, and glucosinolates (GLSs) as adaptive responses. The review also highlights the molecular mechanisms underlying drought tolerance (DT), focusing on gene expression changes, signal transduction pathways, and the critical role of transcription factors (TFs). Abscisic acid (ABA) is pivotal in plant response and tolerance, regulating numerous genes through ABA signaling. TFs are central to genetic regulation under stress conditions, with several TFs, such as ABA-responsive element binding protein/factor (AREB/ABF), WRKY, NAC, and Nuclear factor-Y (NF-Y), modulating gene expression in an ABA-dependent manner. Additionally, certain APETALA2/Ethylene response factors (AP2/ERF) and some NAC TFs govern gene expression independently of ABA. Furthermore, this study has highlighted the regulation of phytohormones and their interaction during drought events and the involvement of gamma-aminobutyric acid (GABA) signaling in DS management. The current study aims to provide a comprehensive understanding of ABA signaling in stomatal closure and the activation of TFs involved in regulating plant responses to DS. It also seeks to develop potential strategies to enhance plant tolerance to drought conditions.