Premium
Melatonin biosynthesis in plants: multiple pathways catalyze tryptophan to melatonin in the cytoplasm or chloroplasts
Author(s) -
Back Kyoungwhan,
Tan DunXian,
Reiter Russel J.
Publication year - 2016
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/jpi.12364
Subject(s) - melatonin , tryptamine , serotonin , tryptophan hydroxylase , tryptophan , biology , biosynthesis , biochemistry , chloroplast , endoplasmic reticulum , enzyme , microbiology and biotechnology , endocrinology , amino acid , gene , receptor , serotonergic
Melatonin is an animal hormone as well as a signaling molecule in plants. It was first identified in plants in 1995, and almost all enzymes responsible for melatonin biosynthesis had already been characterized in these species. Melatonin biosynthesis from tryptophan requires four‐step reactions. However, six genes, that is, TDC , TPH , T5H , SNAT , ASMT , and COMT , have been implicated in the synthesis of melatonin in plants, suggesting the presence of multiple pathways. Two major pathways have been proposed based on the enzyme kinetics: One is the tryptophan/tryptamine/serotonin/ N ‐acetylserotonin/melatonin pathway, which may occur under normal growth conditions; the other is the tryptophan/tryptamine/serotonin/5‐methoxytryptamine/melatonin pathway, which may occur when plants produce large amounts of serotonin, for example, upon senescence. The melatonin biosynthetic capacity associated with conversion of tryptophan to serotonin is much higher than that associated with conversion of serotonin to melatonin, which yields a low level of melatonin synthesis in plants. Many melatonin intermediates are produced in various subcellular compartments, such as the cytoplasm, endoplasmic reticulum, and chloroplasts, which either facilitates or impedes the subsequent enzymatic steps. Depending on the pathways, the final subcellular sites of melatonin synthesis vary at either the cytoplasm or chloroplasts, which may differentially affect the mode of action of melatonin in plants.