Melatonin in crop plants: from biosynthesis through pleiotropic effects to enhanced stress resilience.

Melatonin plays a crucial role in enhancing plant resilience to environmental stresses by regulating physiological and biochemical responses. This review provides an overview of melatonin biosynthesis, signaling pathways, and its interactions with phytohormones, highlighting its multifunctional roles across various crop species. We summarize recent discoveries regarding the biosynthetic pathways of melatonin and its crucial metabolites, emphasizing the importance of tryptophan and serotonin in this process. Furthermore, we discuss the intricate crosstalk between melatonin and phytohormones, particularly auxins, cytokinins, and brassinosteroids, which collectively influence root development, growth, and stress tolerance, among other traits. The antioxidant activity of melatonin and its derivatives, along with their impact on photosynthesis, has also been thoroughly discussed. Notably, melatonin's regulatory actions promote root growth, thereby improving water and nutrient absorption under stress conditions. The identification of candidate genes and a putative receptor provides a foundation for future studies aimed at elucidating the molecular mechanisms underlying melatonin signaling in crop species. Ultimately, this review underscores the potential of harnessing melatonin in crop improvement strategies to enhance resilience to abiotic stresses while promoting sustainable agricultural practices.