Journal of Tea Science Research, 2024, Vol.14, No.6, 304-312 http://hortherbpublisher.com/index.php/jtsr 306 2.3 Influence of environmental and management factors Sensory quality and chemical composition are determined by environmental conditions (altitude, soil, climate) and cultivation practice (methods of processing, storage, cultivar selection). For example, teas grown at high altitude are sweeter and fresher due to lower temperature and unique ecological conditions. Processing operations such as fermentation, withering, and yellowing alter the composition of major metabolites, therefore impacting taste and aroma. Soil properties and microbial population on the other hand are mainly accountable for the accrual of quality traits in tea leaves, and seasonal differences can cause significant changes in the amount of catechin, amino acids, and caffeine. All these combine to determine the regional and seasonal typic of the tea quality (Zhou et al., 2020; Yang et al., 2022; Wu et al., 2025). 3 Key Functional Genes and Metabolic Pathways Regulating Tea Quality 3.1 Genes involved in the biosynthesis of tea polyphenols and catechins Catechins and other polyphenols are major contributors to tea’s taste and health benefits. Their biosynthesis is controlled by structural genes such as chalcone synthase, flavonoid 3',5'-hydroxylase, leucoanthocyanidin dioxygenase, and polyphenol oxidase. MYB transcription factors (e.g., CsMYB8, CsMYB99) play central roles in regulating these pathways. Co-expression network analyses have identified hub genes and modules that coordinate catechin biosynthesis, and environmental factors like light also influence gene expression and metabolite accumulation (Tai et al., 2018; Lu et al., 2024). 3.2 Metabolic pathways related to amino acid synthesis Amino acids, particularly theanine, are responsible for tea's umami flavor. The genes like theanine synthetase and glutamine synthetase regulate the biosynthesis of theanine, being controlled by transcription factors like CsMYB9 and CsMYB49. WRKY transcription factors like CsWRKY53 and CsWRKY40 and abscisic acid (ABA) signaling play a significant role in theanine hydrolysis during postharvest treatment and influence the quality of finished tea. DNA methylation and other epigenetic mechanisms also control amino acid biosynthetic gene expression consistent with seasonal and environmental fluctuations (Qiao et al., 2019; Su et al., 2020; Li et al., 2023). 3.3 Genes involved in caffeine biosynthesis and degradation Caffeine content is determined by N-methyltransferase genes, which have expanded in tea. MYB transcription factors (e.g., CsMYB85, CsMYB86) are involved in caffeine biosynthesis regulation. Comparative genomics shows that tea’s caffeine pathway evolved independently from those in coffee and cacao, with higher expression of caffeine biosynthetic genes correlating with increased caffeine accumulation in certain cultivars (Su et al., 2020). 3.4 Biosynthetic pathways of aromatic compounds Aroma is shaped by the biosynthesis of volatile terpenoids, fatty acid-derived volatiles, and carotenoid-derived volatiles. Key genes include terpene synthases, carotenoid cleavage dioxygenases (CsCCD), and various glycosidases. MYB transcription factors (e.g., CsMYB68, CsMYB147) regulate the production of mono- and sesquiterpenoid volatiles. Alternative splicing and post-transcriptional regulation also play significant roles in modulating aroma compound biosynthesis during tea processing, such as withering and supplementary light exposure (Zhang et al., 2022; Ni et al., 2023; Lu et al., 2024). 4 Roles of Epigenetic Regulation and Transcription Factors in Quality Formation 4.1 Transcriptional regulatory networks Transcription factors (TFs) such as MYB, bHLH, WRKY, and GOLDEN 2-LIKE (GLK) play important roles in regulating the biosynthesis of prominent secondary metabolites (e.g., catechins, theanine, caffeine, flavonoids, and aroma compounds) to determine tea quality. For example, MYB TFs regulate flavonoid, caffeine, and theanine biosynthesis, while WRKY TFs can act as negative regulators of O-methylated catechin biosynthesis. The bHLH family is involved in trichome development and influencing resistance and quality (Qiao et al., 2019). Dynamic gene regulatory networks, especially wound- or environment-stimulated networks, organize the expression of
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