Journal of Tea Science Research, 2025, Vol.15, No.1, 1-11 http://hortherbpublisher.com/index.php/jtsr 3 polymorphisms (SNPs) can explain phenotypic differences in catechin content (Jin et al., 2016). QTL mapping and genome-wide association studies (GWAS) have also identified candidate genes, and molecular markers associated with catechin biosynthesis, providing theoretical support for molecular marker-based breeding of high-quality tea varieties (Koech et al., 2018; 2019; Yamashita et al., 2020). Transcription factors such as the MYB, bHLH, and WRKY families regulate the expression of genes involved in catechin synthesis, exhibiting tissue-specific and developmental stage-specific regulation, thereby controlling catechin accumulation (Maritim et al., 2020; Parmar et al., 2022). Environmental factors such as drought and temperature regulate catechin content by influencing gene expression. Transcriptome and QTL studies have revealed associations between stress-responsive genes and catechin levels (Koech et al., 2019; Maritim et al., 2020). 3.2 Regulation of theanine accumulation Theanine is an amino acid unique to tea leaves, whose synthesis primarily relies on the synergistic action of theanine synthase (TS), glutamine synthase (GS), and glutamate dehydrogenase (GDH). The expansion and functional divergence of the GS gene family are closely associated with the high theanine content in tea leaves (Wei et al., 2018). Transcriptome and genomic studies have shown that the regulation of theanine synthesis involves the expansion of related gene families and includes tea-specific regulatory mechanisms, such as unique gene variants and specific expression patterns. These characteristics lead to significant differences in theanine metabolism between tea plants and their closely related species (Wei et al., 2018; Xia et al., 2020b). Wei et al. (2018) identified a tea plant gene, CsTSI, through phylogenetic analysis, that is highly homologous to bacterial GSI-type glutamine synthases. Tissue expression analysis revealed that it is highly expressed in roots, consistent with the tissue distribution of theanine. The researchers constructed a CsTSI overexpression line in Arabidopsis thaliana and confirmed its ability to synthesize theanine through ethylamine precursor feeding experiments, clarifying its functional role in theanine biosynthesis (Figure 1). 3.3 Aroma biosynthesis networks Tea aroma is composed of a complex network of volatile compounds, dominated by monoterpenes and fatty acid derivatives. Genes encoding enzymes such as terpene synthase (TPS), and lipoxygenase (LOX) are highly expressed in tea varieties with distinctive aroma characteristics (Maritim et al., 2020). The TPS gene family is responsible for the synthesis of monoterpenes, while the LOX pathway produces fatty acid-derived volatiles. Transcriptome analysis and protein-protein interaction studies have revealed that, the coordinated regulation of these pathways, and identified several key candidate genes, providing potential targets for future improvements in tea aroma traits (Maritim et al., 2020; Parmar et al., 2022). 4 Functional Genomics of Stress Resistance Traits 4.1 Cold and drought resistance pathways The abscisic acid (ABA) signaling pathway plays a core role in tea plants' response to abiotic stress. The PYL gene family encodes ABA receptors, and its members are upregulated under drought and low-temperature stress. Some specific genes (like CSS0047272.1) respond in both drought and pathogen infection, indicating signal crossover between abiotic and biological stress pathways (An et al., 2023). Transcription factor families, such as HD-Zip and BZR1, showed stress-responsive expression under cold, drought and salt stress, suggesting their involvement in ABA and other plant hormone-mediated response pathways (Shen et al., 2019; Li et al., 2023a). The expression levels of MYB transcription factors, especially CsMYB45, CsMYB46 and CsMYB105, increased under low temperature and methyl jasmonate treatment, regulating the cold resistance of tea plants through the jasmonic acid signaling pathway (Han et al., 2022). The superoxide dismutase (SOD) gene plays a key role in eliminating ROS accumulated, during low temperatures and drought stress. Most CsSOD genes are induced under low-temperature stress, while CsCSD genes mainly
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