Functional Characterization of Serotonin N-Acetyltransferase Genes (/) in Melatonin Biosynthesis of .

Hypericum perforatum is a traditional medicinal plant that contains various secondary metabolites. As an active component in , melatonin plays important role in plant antioxidation, growth, and photoperiod regulation. Serotonin N-acetyltransferase (SNAT) is the key enzyme involved in the last or penultimate step of phytomelatonin biosynthesis. A total of 48 members of SNAT family were screened and analyzed based on the whole genome data of , and two genes ( and ) were functionally verified to be involved in the biosynthesis of melatonin. It was found that and were highly expressed in the leaves and showed obvious responses to high salt and drought treatment. Subcellular localization analysis indicated that these two proteins were both localized in the chloroplasts by the protoplasts transient transfection. Overexpression of and in (SNAT) and (wild-type) resulted in melatonin content 1.9-2.2-fold and 2.5-4.2-fold higher than that in control groups, respectively. Meanwhile, -overexpressing plants showed a stronger ability of root growth and scavenging endogenous reactive oxygen species. In this study, the complete transgenic plants of were obtained through -mediated genetic transformation for the first time, which laid a significant foundation for further research on the function of key genes in .