Journal of Tea Science Research, 2024, Vol.14, No.6, 344-352 http://hortherbpublisher.com/index.php/jtsr 347 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
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