Phytomelatonin as a key regulator of drought stress adaptation: signaling networks, microbial interactions, and biotechnological potential

The impact of drought stress has remained a major problem that affects crop yield, growth, and development worldwide. There is increasing research interest showing that phytomelatonin acts as an integrative regulator that enhances plant tolerance to drought. Phytomelatonin, which is a potent antioxidant, acts by scavenging the reactive oxygen species (ROS) in plants but its role in drought tolerance is greater than antioxidation. It is of key importance for several physiological and developmental processes involved in plant survival, including seed germination, root development, and leaf senescence. The various pathways in which phytomelatonin mediate drought tolerance are multifaceted and involve molecular mechanisms of signaling. These pathways involve interactions with membrane-bound receptor proteins, notably phytomelatonin receptor 1 (PMTR1), the activation of downstream signaling components like mitogen-activated protein kinase (MAPK) cascades, and various transcription factors that regulate gene expression in response to stress. In this review the molecular mechanisms of phytomelatonin treatment under drought stress have been explored. In addition, it explores innovative approaches to enhance the precision of genetic and metabolic engineering strategies through the application of melatonin, aiming to improve drought tolerance of plants in a comprehensive manner. Melatonin-mediated resistance to drought, partly through activation of plant-associated microbial communities, shows promising effects. However, the underlying mechanisms of how melatonin influences these microbial communities under drought stress remain poorly understood. This review consolidates the research conducted on melatonin, emphasizing this developing field of study. Additionally, it underscores the significance of melatonin's interactions with other phytohormones in facilitating adaptation to drought conditions, aiming to enhance its regulatory functions. Drawing from the aforementioned developments, this review provides a summary of recent advances to systematically explore the impact of melatonin on drought tolerance and describes research directions to improve the understanding of its various implications and applications in sustainable agricultural systems in drought-affected regions.