Melatonin microbe interactions in plant rhizosphere.

Melatonin has emerged as a pivotal molecule in agriculture due to its ability to promote plant growth and alleviate abiotic stresses. Beyond endogenous biosynthesis, plants recruit microbial symbionts that also produce melatonin, which regulates redox balance, systemic resistance, and root development. Although plants and microbes employ distinct yet partially overlapping enzymatic pathways, both contribute to melatonin production under diverse conditions. A major limitation of direct melatonin application is its light sensitivity and instability across soil pH, restricting field-level use. Alternatively, melatonin-producing microbes can enrich soils, enhancing melatonin availability, uptake, and transport within plants to improve stress tolerance and growth. This review synthesizes current understanding of melatonin biosynthesis in plants and microbes, its ecological and physiological roles, and the promise of microbial consortia as delivery systems. We highlight melatonin-based strategies as sustainable tools for crop management and outline future directions for agricultural applications.