Genome-wide identification and characterization of genes involved in melatonin biosynthesis in Morus notabilis (wild mulberry)

Genome Identification of the Tea Plant (Camellia sinensis) ASMT Gene Family and Its Expression Analysis under Abiotic Stress

The tea plant (Camellia sinensis (L.) O. Ktze) is an important cash crop grown worldwide. It is often subjected to environmental stresses that influence the quality and yield of its leaves. Acetylserotonin-O-methyltransferase (ASMT) is a key enzyme in melatonin biosynthesis, and it plays a critical role in plant stress responses. In this paper, a total of 20 ASMT genes were identified in tea plants and classified into three subfamilies based on a phylogenetic clustering analysis. The genes were unevenly distributed on seven chromosomes; two pairs of genes showed fragment duplication. A gene sequence analysis showed that the structures of the ASMT genes in the tea plants were highly conserved and that the gene structures and motif distributions slightly differed among the different subfamily members. A transcriptome analysis showed that most CsASMT genes did not respond to drought and cold stresses, and a qRT-PCR analysis showed that CsASMT08, CsASMT09, CsASMT10, and CsASMT20 significantly responded to drought and low-temperature stresses; in particular, CsASMT08 and CsASMT10 were highly expressed under low-temperature stress and negatively regulated in response to drought stress. A combined analysis revealed that CsASMT08 and CsASMT10 were highly expressed and that their expressions differed before and after treatment, which indicates that they are potential regulators of abiotic stress resistance in the tea plant. Our results can facilitate further studies on the functional properties of CsASMT genes in melatonin synthesis and abiotic stress in the tea plant.

Expanding the application of tryptophan: Industrial biomanufacturing of tryptophan derivatives

Tryptophan derivatives are various aromatic compounds produced in the tryptophan metabolic pathway, such as 5-hydroxytryptophan, 5-hydroxytryptamine, melatonin, 7-chloro-tryptophan, 7-bromo-tryptophan, indigo, indirubin, indole-3-acetic acid, violamycin, and dexoyviolacein. They have high added value, widely used in chemical, food, polymer and pharmaceutical industry and play an important role in treating diseases and improving life. At present, most tryptophan derivatives are synthesized by biosynthesis. The biosynthesis method is to combine metabolic engineering with synthetic biology and system biology, and use the tryptophan biosynthesis pathway of Escherichia coli, Corynebacterium glutamicum and other related microorganisms to reconstruct the artificial biosynthesis pathway, and then produce various tryptophan derivatives. In this paper, the characteristics, applications and specific biosynthetic pathways and methods of these derivatives were reviewed, and some strategies to increase the yield of derivatives and reduce the production cost on the basis of biosynthesis were introduced in order to make some contributions to the development of tryptophan derivatives biosynthesis industry.

Ectopic overexpression of mulberry MnT5H2 enhances melatonin production and salt tolerance in tobacco

Soil salinization severely inhibits plant growth and has become one of the major limiting factors for global agricultural production. Melatonin (N-acetyl-5-methoxytryptamine) plays an important role in regulating plant growth and development and in responding to abiotic stresses. Tryptamine-5-hydroxylase (T5H) is an enzyme essential for the biosynthesis of melatonin in plants. Previous studies have identified the gene MnT5H for melatonin synthesis in mulberry (Morus notabilis), but the role of this gene in response to salinity stress in mulberry is remain unclear. In this study, we ectopically overexpressed MnT5H2 in tobacco (Nicotiana tabacum L.) and treated it with NaCl solutions. Compared to wild-type (WT), melatonin content was significantly increased in the overexpression-MnT5H2 tobacco. Under salt stress, the expression of NtCAT, NtSOD, and NtERD10C and activity of catalase (CAT), peroxidase (POD), and the content of proline (Pro) in the transgenic lines were significantly higher than that in WT. The Malondialdehyde (MDA) content in transgenic tobacco was significantly lower than that of WT. Furthermore, transgenic tobacco seedlings exhibited faster growth in media with NaCl. This study reveals the changes of melatonin and related substance content in MnT5H2-overexpressing tobacco ultimately lead to improve the salt tolerance of transgenic tobacco, and also provides a new target gene for breeding plant resistance to salt.

Phytochemicals, Pharmacological Effects and Molecular Mechanisms of Mulberry

There are numerous varieties of mulberry, and each has high medicinal value and is regarded as a promising source of traditional medicines and functional foods. Nevertheless, the nutrients and uses of mulberry differ from species (Morus alba L., Morus nigra L. and Morus rubra L.). Phenolic compounds are prominent among the biologically active ingredients in mulberry, especially flavonoids, anthocyanins and phenolic acids. Epidemiologic studies suggest that mulberry contains a rich, effective chemical composition and a wide range of biological activity, such as antioxidant, anti-inflammatory, anti-tumor and so on. However, compared with other berries, there has been a lack of systematic research on mulberry, and this hinders its further expansion as a functional fruit. The main purpose of this review is to provide the latest data regarding the effective chemical constituents and pharmacological effects of mulberry to support its further therapeutic potential and health functions.

Molecular Mechanisms Underlying the Biosynthesis of Melatonin and Its Isomer in Mulberry

Mulberry (Morus alba L.) leaves and fruit are traditional Chinese medicinal materials with anti-inflammatory, immune regulatory, antiviral and anti-diabetic properties. Melatonin performs important roles in the regulation of circadian rhythms and immune activities. We detected, identified and quantitatively analyzed the melatonin contents in leaves and mature fruit from different mulberry varieties. Melatonin and three novel isoforms were found in the Morus plants. Therefore, we conducted an expression analysis of melatonin and its isomer biosynthetic genes and in vitro enzymatic synthesis of melatonin and its isomer to clarify their biosynthetic pathway in mulberry leaves. MaASMT4 and MaASMT20, belonging to class II of the ASMT gene family, were expressed selectively in mulberry leaves, and two recombinant proteins that they expressed catalyzed the conversion of N-acetylserotonin to melatonin and one of three isomers in vitro. Unlike the ASMTs of Arabidopsis and rice, members of the three ASMT gene families in mulberry can catalyze the conversion of N-acetylserotonin to melatonin. This study provides new insights into the molecular mechanisms underlying melatonin and its isomers biosynthesis and expands our knowledge of melatonin isomer biosynthesis.