Melatonin-mediated stress signaling in plants: Multilayered networks and translational potential for...

Melatonin, initially identified as an animal hormone, is now well recognized as an essential bioactive molecule in plants, where it regulates a wide range of functions from growth and development to stress adaptation. Accumulating evidence indicates that melatonin is ubiquitously present across diverse plant species and plays key roles in physiological processes such as seed germination, root and shoot development, protection of the photosynthetic apparatus, and fruit ripening. Importantly, melatonin functions as a potent antioxidant and signaling molecule, enabling plants to cope with various abiotic and biotic stresses, including drought, salinity, temperature extremes, heavy metal toxicity, and pathogen attack. These protective effects are mediated through efficient scavenging of reactive oxygen and nitrogen species, enhancement of antioxidant enzyme activities, modulation of stress-responsive gene expression, and extensive crosstalk with phytohormones such as abscisic acid, salicylic acid, and ethylene. Recent advances in elucidating melatonin biosynthesis and subcellular localization have further revealed its organelle-specific functions and broader involvement in plant metabolic regulation and stress resistance. Moreover, exogenous application of melatonin through seed priming, foliar application, or postharvest treatments has been shown to enhance plant growth, yield, and stress tolerance, while genetic manipulation of melatonin biosynthetic pathways offers promising strategies for developing climate-resilient crop varieties. Together, these findings underscore the potential of melatonin as a safe and versatile regulator in sustainable agriculture, contributing to improved crop productivity and food security under increasingly challenging environmental conditions.