Phytomelatonin: Biosynthesis, Signaling, and Functions.

Phytomelatonin has attracted significant attention over the years for its roles in promoting plant growth and enhancing stress resistance. The biosynthetic pathway of phytomelatonin is more intricate than that of melatonin in animals, occurring in plants in the endoplasmic reticulum, chloroplasts, mitochondria, and cytoplasm. By compartmentalizing phytomelatonin production within specific organelles and differentially expressing biosynthesis genes, plants may finely tune the levels of this hormone under normal growth conditions, as well as in rapid responses to changing environmental conditions. Phytomelatonin can interact with its receptor PMTR1, triggering G protein signaling, initiating ROS-Ca2+ signaling hubs, and activating MAPK cascades. Phytomelatonin's main role is promoting plant growth and development, whereas phytomelatonin-mediated resistance to numerous abiotic and biotic stresses is inducible and primed. The flexibility in the biosynthesis, together with the signaling pathways influenced, may contribute to phytomelatonin balancing the trade-offs between growth and stress resistance.