Melatonin (MT), also called the hormone of darkness, exists in all forms of life. In plants, MT is termed phytomelatonin (PMT). Progress has been made in the past 30 years in understanding the biosynthesis of tryptophan-derived PMT, and most of the associated genes have been cloned successfully.

In a study published in Annual Review of Plant Biology, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and the collaborators discussed the biosynthesis, signal transduction, and function of the plant hormone PMT, and highlighted the critical role of PMT in enhancing crop growth and stress resistance without compromising yield, which has profound implications for global food security.

Researchers first evaluated the concentrations of PMT across a wide spectrum of plants, from unicellular algae to mosses, ferns, gymnosperms, and higher plants. They found that PMT is universally present in plants at low concentrations.

PMT operated through unique biosynthetic and signaling pathways. Plants synthesize PMT across multiple cellular compartments, including the cytoplasm, chloroplasts, and mitochondria. This compartmentalized production, combined with differential expression of biosynthesis genes, enables plants to precisely modulate PMT levels. Such flexibility allows rapid adjustments to environmental shifts while maintaining growth under optimal conditions—a dual capability.

In detail, plants were able to fine-tune PMT levels for normal growth conditions as well as in response to rapidly changing environmental conditions, through compartmentalized production in specific cell organelles and differential expression of genes. Under favorable conditions, PMT prioritized developmental processes. When stresses emerged, however, it redirected resources to fortify cellular defenses—such as antioxidant production and stress-responsive gene activation—without compromising long-term viability.

Researchers proposed two cost-effective strategies to harness PMT's potential, including exogenous application of optimal melatonin concentrations to crops and boosting endogenous PMT levels via genetic engineering.

“As the challenge of global food security intensifies, the dual function of PMT in enhancing both yield and resilience places it at the vanguard of agricultural innovation. More studies on its biosynthesis and signaling pathways may contribute to sustainable agriculture,” said CHEN Qi from XTBG, the first author of this study.