Abstract
Hypericum perforatum is a traditional medicinal plant that contains various secondary metabolites. As an active component in H. perforatum, 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 H. perforatum, and two SNAT genes (HpSNAT1 and HpSNAT2) were functionally verified to be involved in the biosynthesis of melatonin. It was found that HpSNAT1 and HpSNAT2 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 Arabidopsis protoplasts transient transfection. Overexpression of HpSNAT1 and HpSNAT2 in Arabidopsis (SNAT) and H. perforatum (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, SNAT-overexpressing Arabidopsis plants showed a stronger ability of root growth and scavenging endogenous reactive oxygen species. In this study, the complete transgenic plants of H. perforatum were obtained through Agrobacterium-mediated genetic transformation for the first time, which laid a significant foundation for further research on the function of key genes in H. perforatum.
Highlights
The Quantitative real-time PCR (qPCR) results were consistent with the expression pattern of HpSNAT1 and HpSNAT2 in different tissue transcriptome sequencing results, indicating that the two genes were highly expressed in leaves (Figure 1C)
Through the analysis of cisacting elements in the promoter region of the two genes, it was found that both two genes contain gibberellic acid (GA), methyl jasmonate (MeJA), salicylic acid (SA), auxin (IAA), abscisic acid (ABA), and stress response elements of low temperature, drought, and injury
HpSNAT1 contains flavonoids biosynthesis and elements related to plant circadian rhythm regulation, while HpSNAT2 contains ethylene response and elements related to gene expression regulation in plant meristem
Summary
As an important bioactive component in H. perforatum, melatonin (N-acetyl-5methoxytryptamine) is a ubiquitous multifunctional substance acting as a free radical scavenger, Functional Characterization of HpSNAT1/2 circadian rhythm regulator, and immune regulatory molecule (Galano et al, 2011; Manchester et al, 2015; Ma et al, 2020). It can induce antidepressant effects (Detanico et al, 2009), regulate some nerve regeneration processes (Atik et al, 2011), and protect organisms from environmental and internal oxidative stress (Galano and Reiter, 2018). It has been reported that melatonin can regulate the whole growth and development stage of plants, from promoting seed germination to delaying leaf senescence; and enhance the tolerance of plants to abiotic and biotic stresses, such as drought and salt stress, osmotic stress, extreme temperature, senescence, and pathogen attacks (Lee et al, 2014; Li et al, 2015; Liang et al, 2015; Han et al, 2017)
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