In plants, 5mC DNA methylation is an important and conserved epistatic mark involving genomic stability, gene transcriptional regulation, developmental regulation, abiotic stress response, metabolite synthesis, etc. However, the roles of 5mC DNA methylation modification (5mC methylation) in tea plant growth and development (in pre-harvest processing) and flavor substance synthesis in pre- and post-harvest processing are unknown. We therefore conducted a comprehensive methylation analysis of four key pre-harvest tissues (root, leaf, flower, and fruit) and two processed leaves during oolong tea post-harvest processing. We found that differential 5mC methylation among four key tissues is closely related to tissue functional differentiation and that genes expressed tissue-specifically, responsible for tissue-specific functions, maintain relatively low 5mC methylation levels relative to non-tissue-specifically expressed genes. Importantly, hypomethylation modifications of CsAlaDC and TS/GS genes in roots provided the molecular basis for the dominant synthesis of theanine in roots. In addition, integration of 5mC DNA methylationomics, metabolomics, and transcriptomics of post-harvest leaves revealed that content changes in flavor metabolites during oolong tea processing were closely associated with transcription level changes in corresponding metabolite synthesis genes, and changes in transcript levels of these important synthesis genes were strictly regulated by 5mC methylation. We further report that some key genes during processing are regulated by 5mC methylation, which can effectively explain the content changes of important aroma metabolites, including α-farnesene, nerolidol, lipids, and taste substances such as catechins. Our results not only highlight the key roles of 5mC methylation in important flavor substance synthesis in pre- and post-harvest processing, but also provide epimutation-related gene targets for future improvement of tea quality or breeding of whole-tissue high-theanine varieties.

Catechins are the major flavor substances in teas, which have a variety of health effects; however, high catechin and high sensory quality are a pair of contradictions that are difficult to coordinate. To explore the processing procedure with high catechins and high sensory quality, a single-factor processing experiment was carried out over the processing production of oolong tea. Combined with orthogonal partial least square discriminant analysis (OPLS-DA), correlation analysis, and principal component analysis (PCA), the optimal production procedure for oolong tea is as follows: red light withering for 8 h, leaf rotating for 10 min with a total standing time for 8 h, drum roasting for 5 min at 290 °C, low-temperature rolling (flattening at 4 °C for 5 min, without pressure for 1 min and under pressure for 5 min), microwave drying (800 W for 7.5 min). This study demonstrates a significant increase in the retention of catechins, which contributes to the mellow and brisk tastes of oolong tea, addressing the challenge of catechin content and sensory quality. Our study provides a novel insight into the relationship between the oolong tea processing and flavor formation.

High-aroma Camellia sinensis cultivars Jinguanyin and Jinmudan are usually used to make black tea and lightly fermented oolong tea. The Oolong tea produced has a rich, lingering aroma and high quality. However, tea green leafhoppers can significantly reduce both yield and quality. Therefore, this study investigated the impact of varying degrees of tea green leafhopper damage on the volatile compounds of Oolong tea which made from Jinguanyin and Jinmudan according to the heavy-fermentation beauty tea process. The volatile profiles were analyzed by GC–MS. Results indicated that medium degree of puncturing by tea green leafhoppers enhanced the formation and accumulation of volatiles in Oolong tea made from Jinguanyin. We also found that Linalool, Geraniol, Dihydrolinalool and (Z)-linalooloxide(furanoid) were identified as key volatile compounds contributing to unique floral, fruity and sweet aroma of Jinguanyin and Jinmudan oolong tea. And the contents in JGYTM were the highest at 2749.98 μg/kg, 24751.63 μg/kg, 17131.17 μg/kg and 8172.35 μg/kg, respectively. The OAV values were 1833.32, 3300.22, 155.74 and 24,517.1, respectively. The content of geraniol in JMDTH was the highest at 22973.28 μg/kg, with an OAV value of 3063.1. The contents of linalool, dihydrolinalool and (Z)-linalooloxide(furanoid) were the highest in JMDTL, at 2207.25 μg/kg, 10080.36 μg/kg and 7441.64 μg/kg, respectively, with OAV values of 1471.5, 91.64 and 22,324.9, respectively. Therefore, the medium and low levels of puncture caused by the tea green leafhoppers respectively impart unique floral and fruity scents as well as sweet aromas to the Jinguanyin and Jinmudan Oolong teas. This study provides technical reference for the cultivation and management of Jinguanyin and Jinmudan, and provides theoretical basis for the improvement of raw materials and aroma of Oriental beauty tea in oolong tea.

Ecological factors directly influence the growth and metabolism of tea plants (Camellia sinensis L.), and unfavorable environmental conditions cause abiotic stress to them. Abiotic stress causes damage to reliable, high-quality, and safe tea production, yet the optimal ecological conditions for enhancing both yield and quality remain unclear. To investigate the response patterns of shoot growth to ecological factors and its relationship with catechin accumulation, this study conducted the cultivation of tea plants with a precise modulation of both individual and combined ecological parameters. Under 30 °C and 90% air humidity, specific combinations of light intensity and substrate relative humidity (“250 µmol·m⁻²·s⁻¹ + 65%” or “350 µmol·m⁻²·s⁻¹ + 70%”) significantly enhanced growth and yield. A significant correlation between shoot growth and catechin accumulation was observed, and mathematical models further revealed a synergistic response between shoot growth capacity and total catechin content to ecological factors. Furthermore, co-expression analysis indicated that catechin biosynthesis-related genes exhibited coordinated expression with key growth-related genes, including CsTCP, CsErf, and CsXth. In conclusion, these findings identify optimal ecological conditions to mitigate abiotic stress and reveal a synergistic relationship between catechin biosynthesis and shoot growth, providing an ecological basis for balancing yield and quality in tea production.

Epigallocatechin gallate (EGCG) imparts distinctive health benefits and flavor to tea, and its accumulation is modulated by plant growth regulators (PGRs). However, the regulatory mechanisms of Paclobutrazol (PAC) and Lovastatin (LS) underlying EGCG biosynthesis remain uncharacterized. We integrated quantitative analysis, transcriptomics, and metabolomics to investigate the regulatory effects of exogenous PAC and LS on EGCG accumulation in tea plants and systematically elucidate the underlying molecular mechanism governing EGCG biosynthesis. The results demonstrated that exogenous PAC and LS treatments significantly elevated the accumulation of EGCG, as well as endogenous auxin and jasmonic acid (JA) contents. The variation trend of these key metabolites was highly consistent with the accumulation patterns of upstream flavonoid components, including eriodictyol, delphinidin, and epigallocatechin. Transcriptomic profiling further verified the critical involvement of auxin and JA signal transduction pathways in PGR-induced EGCG differential accumulation, and we screened a total of 14 auxin-related and 8 JA-related core signal regulatory factors. Furthermore, integrated bioinformatic analyses and antisense oligonucleotide (AsODN) functional validation experiments revealed that the core hormone signaling genes CsARF2 and CsMYC2 regulate the expression of CsSCPL16 through the transcription factor CsMYB80, and ultimately promote the conversion of epigallocatechin to EGCG and promote the accumulation of EGCG in tea plants. Collectively, the PGRs boost EGCG biosynthesis by mediating endogenous auxin and JA signal transduction. These results support the development of targeted agronomic practices to improve tea quality and lay a theoretical basis for expanding the industrial exploitation of tea bioactive constituents.