Journal of Tea Science Research, 2024, Vol.14, No.6, 313-321 http://hortherbpublisher.com/index.php/jtsr 314 The study provides a comprehensive overview of the recent advances in secondary metabolic pathways and their regulations in Camellia sinensis. It encapsulates the major secondary metabolites, biosynthetic pathways, and genetic and epigenetic regulations. By integrating multi-omics and functional studies, the review presents a shared framework to enhance an understanding of tea secondary metabolism. The acquired knowledge is important for onward basic plant science and has applied implications for molecular breeding for tea quality and stress tolerance enhancement, towards sustainable tea cultivation and industry development. 2 Major Secondary Metabolites in Tea Plants and Their Functions 2.1 Polyphenols and alkaloids Polyphenols, especially catechins, flavonoids, theaflavins, and thearubigins, are the most abundant and significant bioactive compounds in tea. They contribute to the antioxidant, anti-inflammatory, anticancer, and cardiovascular protective effects of tea, and are key determinants of tea’s taste, color, and health benefits (Li et al., 2022). Alkaloids such as caffeine, theobromine, and theophylline are present in tea leaves. Caffeine is the most prominent, contributing to tea’s stimulating effects and bitterness, while also playing a role in plant defense against herbivores and pathogens (Kottawa-Arachchi et al., 2018). 2.3 Volatile aromatic compounds Volatile compounds, including terpenoids, alcohols, aldehydes, and esters, are responsible for the characteristic aroma and flavor of tea. Key volatiles like linalool, geraniol, and methyl salicylate are crucial for tea quality and are influenced by both genetics and processing methods (Liu et al., 2024). 2.4 Amino acids and other functional compounds Amino acids, particularly theanine, contribute to the umami taste and sweetness of tea. They also have calming effects and are important for the overall flavor profile and health benefits of tea (Kang et al., 2024). Other notable compounds include polysaccharides, vitamins, minerals, and saponins, which contribute to the nutritional value, immune regulation, and additional health-promoting properties of tea (Luo et al., 2023). 3 Elucidation of Secondary Metabolic Pathways 3.1 Phenylpropanoid pathway and flavonoid biosynthesis Phenylpropanoid pathway is the central pathway in tea flavonoid biosynthesis, a group of compounds with primary importance to tea quality and resistance in plants. In plants, it is an enzyme cascade tightly controlled by transcription factors such as MYB, bHLH, and WD-repeat proteins. Recent transcriptomic research has discovered widespread gene expression and regulatory network differences among tea cultivars and identified AP2/ERF, WRKY, NAC, and MYB transcription factors to be involved in controlling both phenylpropanoid and flavonoid biosynthesis (Li et al., 2022). Flavonoid biosynthesis branches out into multiple sub-pathways to produce catechins, anthocyanins, and other compounds contributing to tea flavor and its health-promoting properties (Liu et al., 2021; Pratyusha and Sarada, 2022). 3.2 Terpenoid biosynthesis via MVA and MEP pathways Terpenoids, responsible for much of tea’s aroma, are synthesized through the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. Transcriptome data reveal that tea flowers accumulate higher levels of terpenoids than leaves, largely due to elevated expression of terpene synthase genes. The regulation of terpenoid biosynthesis differs between tissues, suggesting specialized control mechanisms in flowers versus leaves (Xia et al., 2017). 3.3 Purine metabolism and caffeine biosynthesis Caffeine biosynthesis in tea plants proceeds via the purine alkaloid pathway, involving key enzymes such as S-adenosyl methionine synthase (SAMS), xanthosine methyltransferase (XMT), and caffeine synthase (TCS). Comparative transcriptomics between Camellia sinensis varieties have revealed that differences in caffeine and theobromine content are linked to the expression of these genes and their regulation by MYB and AP2/ERF transcription factors (Wang et al., 2025). The tea tree genome also shows lineage-specific expansions of caffeine biosynthetic genes, supporting the independent evolution of this pathway in tea.
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