1 Introduction

Tea (Camellia sinensis) is one of the most widely consumed beverages worldwide, valued not only for its unique flavor and aroma but also for its notable health benefits. As a perennial evergreen shrub, tea has significant economic, cultural, and nutritional importance, especially in Asia and increasingly in global markets. Among the diverse bioactive compounds present in tea leaves, catechins—a subclass of flavonoids—are particularly important due to their roles in determining the sensory qualities of tea and contributing to its functional properties.

Catechins influence key aspects of tea quality, such as astringency, bitterness, and color, and serve as key determinants of consumer preference. They also exhibit remarkable pharmacological effects, including antioxidant, anti-inflammatory, anticarcinogenic, and cardioprotective activities (Xiang et al., 2021; Yu et al., 2021). These health-promoting properties have made catechins a focal point of research in plant science, nutrition, and pharmacology.

The biosynthesis of catechins in tea plants originates from the phenylpropanoid pathway and its downstream flavonoid branches. This process is regulated by a complex network of structural genes, transcription factors such as MYB, bHLH, and WD40, and post-transcriptional and epigenetic mechanisms. Understanding this regulatory network is essential not only for elucidating the metabolic architecture of tea plants but also for facilitating genetic improvement through molecular breeding and biotechnology (Li et al., 2022; Zhao et al., 2023).

The objective of the present review is to represent recent advancement in research in the field of catechin biosynthesis and regulation in tea plants in a systematic way. Major focus is given on the identification of crucial structure and regulatory genes, multi-omics technology, and novel regulatory factors such as non-coding RNAs and epigenetic modifications. With the addition of genomics, transcriptomics, and metabolomics information, this study aims to provide a comprehensive perspective of catechin metabolism and offer strategic recommendations for tea breeding superior, functional tea cultivars.

2 Types and Functional Characteristics of Catechins in Tea Plants

2.1 Major types and relative contents of catechins

Camellia sinensis tea crops produce several major catechins, including epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) (Jin et al., 2023). EGCG is typically the most abundant, especially in green tea, and its formation is achieved through some routes of the flavonoid biosynthesis pathway (Ahmad et al., 2020). Galloylated catechins (EGCG, ECG) contribute up to 75% of the soluble catechins in the tea leaf, while the total catechins are responsible for 8-24% of dry leaf weight (Ahmad et al., 2020). The ratio of each catechin is relative to the tea variety, leaf development stage, and environmental conditions such as light and temperature (Xiang et al., 2021).

2.2 Role of catechins in tea quality

Catechins are key determinants of tea’s sensory qualities, particularly astringency and bitterness (Ahmad et al., 2020). Galloylated catechins (EGCG, ECG) contribute most to astringency and the characteristic taste of green tea (Ahmad et al., 2020). The enzymatic oxidation of catechins during tea processing leads to the formation of theaflavins and thearubigins, which are important for the color and flavor of black and oolong teas. Genetic variation in catechin biosynthetic genes, such as F3′,5′H and CHS, influences catechin content and thus tea quality, providing targets for breeding programs (Jiang et al., 2020).

2.3 Nutritional and pharmacological activities of catechins

Catechins, especially EGCG, exhibit strong antioxidant, anti-inflammatory, and anticancer properties (Rashidinejad et al., 2021). They neutralize reactive oxygen and nitrogen species, contributing to the prevention of various cancers (lung, breast, esophageal, stomach, liver, prostate). Catechins also support cardiovascular health, modulate immune responses, and may have antibacterial and antidiabetic effects (Rashidinejad et al., 2021). However, their bioavailability can be limited by poor stability and absorption, which is an area of ongoing research for functional food applications (Jin et al., 2023).

3 Biosynthetic Pathways of Catechins

3.1 Overview of the phenylpropanoid and flavonoid biosynthesis pathways

Catechins in Camellia sinensis are synthesized via the phenylpropanoid and flavonoid pathways. The process begins with phenylalanine, which is converted through a series of enzymatic steps into flavonoid intermediates, ultimately leading to the production of catechins. These pathways involve multiple gene families and are tightly regulated at both the transcriptional and post-transcriptional levels (Zhu et al., 2025).

3.2 Key structural genes involved in catechin biosynthesis

Key structural genes in catechin biosynthesis include phenylalanine ammonia-lyase (PAL), 4-coumarate:CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), leucoanthocyanidin reductase (LAR), and anthocyanidin reductase (ANR) (Kausar et al., 2020; Zhu et al., 2025). Recent research has identified DFR as an important regulatory factor in controlling flux through the catechin pathway (Kausar et al., 2020). Further, genes CsCHIc, CsF3'H, and CsANRb have been implicated to be responsible for catechin content, and transcription factors MYB, bHLH, and MADS are regulatory (Wang et al., 2018). For galloylated catechins, some acyltransferases and galloyltransferases are also involved (Jin et al., 2023; Zhu et al., 2025) (Figure 1).

3.3 Tissue specificity and developmental regulation of biosynthetic pathways

Catechin biosynthesis is highly tissue- and development-specific. The highest catechin concentrations are typically found in young leaves, with lower levels in stems and roots (Wang et al., 2018). Transcriptome analyses reveal that the expression of biosynthetic genes and their regulatory transcription factors varies across developmental stages and tissues, reflecting the dynamic regulation of catechin accumulation during leaf development (Guo et al., 2017). Coexpression patterns and subcellular localization studies further support the tissue-specific regulation of these pathways (Wang et al., 2018).

4 Transcriptional Regulatory Networks and Key Transcription Factors

4.1 Functional studies on MYB, bHLH, WD40 and other transcription factors

R2R3-MYB transcription factors play a fundamental role in controlling catechin biosynthesis in Camellia sinensis. There are 118 R2R3-MYB proteins identified systematically with some subgroups tea-specialized or expanded, suggesting their fundamental function during the evolutionary diversification of tea-specialized metabolites. Surprisingly, certain R2R3-MYBs are highly expressed in young leaves and apical buds, where galloylated catechins such as ECG and EGCG are stored (Li et al., 2022b). CsMYB34, a R2R3-MYB that is genus-specific, was found to directly regulate the biosynthesis of galloylated catechins through the promoter binding of the biosynthetic gene CsSCPL4 and its resultant positive regulation on its expression (Xu et al., 2024).

4.2 Formation mechanisms and regulatory models of the MBW complex

The MBW complex, composed of MYB, bHLH, and WD40 proteins, is a well-established regulatory module in flavonoid biosynthesis. While the specific assembly and function of the MBW complex in tea plants are still being elucidated, evidence from other plant systems and the identification of MYB and bHLH factors in tea suggest a similar regulatory mechanism. These complexes coordinate the expression of structural genes involved in catechin biosynthesis, enabling precise spatial and temporal control of metabolite accumulation (Li et al., 2022a; Shi et al., 2024).

4.3 Comparative expression and functional analysis of regulatory factors among different cultivars

Comparative studies across tea cultivars reveal that the expression levels of key MYB transcription factors, such as CsMYB34, are positively correlated with galloylated catechin content. In a survey of 19 tea varieties, higher CsMYB34 expression consistently matched increased levels of galloylated catechins, highlighting its role in cultivar-specific metabolite profiles (Xu et al., 2024). Such findings underscore the genetic basis for variation in catechin content and provide targets for breeding programs aimed at enhancing tea quality.

5 Epigenetic Regulation and Non-coding RNAs

5.1 Advances in DNA methylation and histone modifications in catechin regulation

Epigenetic mechanisms such as histone modifications and DNA methylation are major non-sequence-changing regulators of gene expression. These epigenetic modifications can influence the expression of secondary metabolite biosynthesis-related genes, including catechins. Recent studies highlight that histone modifications and DNA methylation are reversible, dynamic, and part of a multifaceted regulatory mechanism with the capability to impact plant metabolic pathways (Bure et al., 2022). Although most research has been targeted to disease and human models, the principles of epigenetic regulation can be applied broadly to plant systems.

5.2 miRNAs and lncRNAs targeting structural genes or transcription factors

Non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), are emerging as the key regulators in epigenetic control. miRNAs can suppress mRNAs encoding structural enzymes or transcription factors, triggering post-transcriptional gene silencing. lncRNAs can modulate gene expression through interaction with DNA, RNA, or proteins, and have been functionally classified as scaffolds or decoys for chromatin-modifying complexes (Wei et al., 2017). These ncRNAs are part of feedback mechanisms that control gene expression, and their regulatory roles are actively being explored in various biological contexts (Kondo et al., 2017).

5.3 Integrative models of epigenetic and transcriptional regulation

Emerging models suggest that epigenetic modifications and non-coding RNAs are interconnected, forming complex regulatory networks. For example, ncRNAs can recruit histone-modifying enzymes to specific genomic loci, while histone modifications can influence the expression of ncRNAs themselves (Kazimierczyk and Wrzesinski, 2021). This mutual regulation enables precise and context-dependent control of gene expression, which is essential for the dynamic regulation of secondary metabolite pathways such as catechin biosynthesis.

6 Application of Multi-omics Approaches in Catechin Research

6.1 Genomic and transcriptomic insights into key gene expression patterns

High-throughput genomics and transcriptomics enable the identification and quantification of genes involved in catechin biosynthesis. Integrative analysis of these data types reveals expression patterns of structural and regulatory genes, helping to map the genetic networks underlying catechin accumulation. Machine learning and network-based approaches are increasingly used to interpret these complex datasets, allowing for the discovery of key gene modules and regulatory elements (Reel et al., 2021; Chen et al., 2023).

6.2 Metabolomics for tracing catechin accumulation and metabolic flux

Metabolomics allows for direct quantification of catechin content and relevant metabolites, giving a snapshot of tea tissue metabolic flux. Combined with transcriptomic and genomic data, metabolomics is employed to follow the pathway of precursors and intermediates, bridging gene expression and metabolite accumulation. Multi-omics integration approaches, comprising data-driven and knowledge-based workflows, are employed to correlate metabolite profiling with gene activity to elucidate catechin biosynthesis dynamics (Wörheide et al., 2021).

6.3 Proteomics and epigenomics revealing hierarchical regulatory structures

Proteomics adds another layer by quantifying the abundance and modification of enzymes and regulatory proteins in catechin pathways. Epigenomics, like DNA methylation and histone modification profiling, illustrates how gene expression is controlled at the chromatin level. Together, these omics layers reveal hierarchical regulatory networks, from epigenetic marks to protein complexes, that control catechin biosynthesis (Subramanian et al., 2020; Chen et al., 2023).

6.4 Case study: Integrated omics analysis of high-catechin cultivars

Integrated multi-omics analyses—combining genomics, transcriptomics, metabolomics, and proteomics—have been applied to compare high- and low-catechin tea cultivars. These studies identify cultivar-specific gene expression patterns, metabolite profiles, and regulatory networks that explain differences in catechin content. Such integrative approaches are essential for pinpointing biomarkers and candidate genes for breeding high-catechin tea varieties (Subramanian et al., 2020; Valous et al., 2024).

7 Prospects for Molecular Breeding and Application of Catechin Regulation

7.1 QTL mapping and development of molecular markers related to catechins

Quantitative trait loci (QTL) mapping and association analysis have also identified significant genetic variants determining catechin content. Notably, functional single nucleotide polymorphisms (SNPs) in the flavonoid 3',5'-hydroxylase (F3'5'H) gene and chalcone synthase (CHS) gene are most significantly involved with catechin profile variations. These markers explain considerable phenotypic variation and are highly effective in marker-assisted selection for improving tea quality in breeding programmes (Jin et al., 2016; Jiang et al., 2020).

7.2 Application of gene editing technologies (e.g., CRISPR) in functional validation and breeding

While direct reports of CRISPR use in tea are limited, functional validation of candidate genes through transgenic and molecular approaches has been demonstrated. For example, manipulation of CsMYB1 and other transcription factors has clarified their roles in catechin biosynthesis and trichome development, providing targets for future gene editing to enhance desirable traits (Li et al., 2022b; Zhang et al., 2025).

7.3 Development of functional tea products and catechin optimization strategies

Understanding natural allelic variation and regulatory mechanisms enables the development of tea cultivars with optimized catechin content for health and flavor. The identification of key regulators, such as CsMYB1 and WRKY transcription factors, offers strategies to breed or engineer tea plants with higher levels of specific catechins, supporting the creation of functional tea products with enhanced health benefits (Luo et al., 2018; Li et al., 2024; Tuo et al., 2024).

7.4 Regulatory mechanisms and application potential in response to environmental stress

Hormone- and environment-mediated regulation of CsSCPL genes in tea plants is closely related to catechin biosynthesis and adaptation to the environment. CsMYB1, for instance, is pivotal as a transcription factor to regulate coordinately trichome formation and catechin production—characters subjected to selection in domestication to enhance stress tolerance and flavor. Besides, regulatory modules CsPHRs-CsJAZ3 and CsHSFA-CsJAZ6 play roles in mediating nutrient deficiency and heat stress responses, respectively, uncovering molecular mechanisms for the tea plant to maintain catechin accumulation under stress. These findings offer promising molecular targets for breeding tea cultivars that are not only catechin-enriched but also stress-resilient (Ahmad et al., 2020; Li et al., 2022a; Zhang et al., 2023) (Figure 2).

8 Concluding Remarks

Biosynthesis of catechin in tea leaves is regulated by a cluster of phenylpropanoid and flavonoid pathway structural genes that are involved in CHS, ANR, and SCPL enzymes. Transcriptional profiling and gene co-expression network analysis identified thousands of differentially expressed genes and highlighted the roles of transcription factors—MYB, bHLH, and WD40—in controlling catechin accumulation throughout leaf development and upon environmental stimulation. The research has also recently shown the function of TCP and GLK transcription factors, which process developmental and environmental information to enhance catechin biosynthesis.

Transcriptional control lies at the heart of catechin metabolism, with MYB-bHLH-WD40 (MBW) complexes and additional transcription factors (e.g., CsMYB1, CsTCPs, CsGLKs) activating or repressing biosynthetic genes directly. Epigenetic control through promoter insertions and chromatin remodeling also regulates gene expression, as in the domestication selection of CsMYB1 alleles for enhanced catechin content and stress tolerance. Multi-omics approaches—combining genomics, transcriptomics, metabolomics, and proteomics—have enabled the identification of hub genes, regulatory modules, and environmental factors (light, temperature, and nutrients) that in combination specify catechin profiles in different cultivars and tissues.

The integration of functional genomics and molecular breeding holds great promise for developing high-quality tea cultivars with optimized catechin content. Marker-assisted selection, QTL mapping, and gene editing technologies are poised to accelerate the breeding of tea plants with desirable flavor, health benefits, and environmental resilience. Continued application of multi-omics and systems biology will deepen our mechanistic understanding and facilitate the rational design of functional tea products tailored to consumer and agronomic needs.

Acknowledgments

We would like to thank Professor Wang for his guidance and support during this study. 

Conflict of Interest Disclosure

The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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