Molecular Plant Breeding 2025, Vol.16, No.5, 278-286 http://genbreedpublisher.com/index.php/mpb 279 etc. These substances endow tea with various flavors such as floral, fruity and nutty aromas (Yin et al., 2022; Yu et al., 2023; Yang et al., 2024). Non-volatile components, such as catechins, amino acids, sugars and caffeine, can affect the freshness, bitterness and richness of tea soup (Xia et al., 2017; Wang et al., 2022). Different types of tea vary greatly in the types and contents of these components, which determines their respective flavor characteristics (Han et al., 2016; Liu et al., 2023; Ma et al., 2023). 2.2 Biosynthetic pathways for terpenoids, phenylpropanoids, and amino acid derivatives Terpenoids are mainly synthesized through the mevalonic acid (MVA) and methyl erythritol phosphate (MEP) pathways. Terpene synthase (TPS) is the key enzyme. In high-aroma tea tree varieties, this gene family shows significant amplification (Xia et al., 2017; Wang et al., 2021a). Phenylpropanes are derived from phenylalanine and are generated through multiple reactions such as phenylalanine ammonia-lyase (PAL) (Yin et al., 2022). Amino acid derivatives are derived from the degradation and transformation of amino acids such as tryptophan and phenylalanine (Yang et al., 2024). Fatty acid degradation and carotenoid cleavage can also produce key aroma substances, such as β -violet ketone and β -cyclocitral (Yin et al., 2022). 2.3 Genetic determinants and transcriptional regulation of flavor-related metabolites The genetic basis of tea tree aroma and flavor is very complex, involving many structural genes and regulatory factors. In high-aroma varieties, the amplification and structural changes of terpene synthase (TPS) family genes promoted the accumulation of terpene aroma substances (Wang et al., 2021a). The synthetic genes of phenylpropanes and amino acid derivatives are also affected by structural variations and allelic imbalance (Xia et al., 2017). Transcription factors such as MYB and bHLH are crucial in regulating the gene expression of flavor metabolism pathways (Gohain et al., 2012). Li et al. (2024) found that epigenetic regulation, such as reduced methylation in the promoter region and enhanced chromatin accessibility, would increase the expression of key aroma synthesis genes, leading to a greater accumulation of specific aroma components. Alternative splicing (AS), as a post-transcriptional regulatory mechanism, also affects the expression of flavor-related genes and the formation of aroma substances (Qiao et al., 2024). 3 Molecular Breeding Tools and Strategies 3.1 Marker-assisted selection (MAS) for aroma and flavor traits Marker-assisted selection (MAS) can efficiently screen out genotypes related to aroma and flavor through the linkage relationship between molecular markers and target traits. In tea plants, MAS has been used to screen genotypes related to the synthesis of aromatic substances (such as terpenoids, alcohols, and esters), enhancing the breeding efficiency of high-quality aroma and flavor traits. For instance, the contents of certain aromatic substances (such as (R)-linalool, β -violetone, etc.) are closely related to the expression levels of their synthase genes. MAS can help quickly identify highly expressed genotypes for breeding (Li et al., 2022b; Liu et al., 2025). In addition, MAS has also shown great value in screening tea tree germplasms with flavor-related traits such as high amino acids and low caffeine (Zhao et al., 2022). 3.2 Quantitative trait loci (QTL) mapping and genome-wide association studies (GWAS) QTL mapping and GWAS are core methods for studying the genetic basis of tea tree aroma and flavor. Through high-density molecular markers and large-scale population analysis, researchers have identified multiple QTLS and candidate genes related to aroma and flavor in tea plants. GWAS studies based on pan-genome and large-scale SNP data have revealed a strong association between allelic variations and flavor chemical components (such as flavonoids, terpenoids, etc.), providing targets for molecular design breeding (Yu et al., 2020). The combined use of QTL and GWAS helps to precisely locate the major genes and regulatory networks that affect aroma and flavor, and accelerate the breeding of high-quality tea tree varieties (Zhang et al., 2021; Chen et al., 2023). 3.3 Genomic selection (GS) and haplotype-based breeding approaches Genomic selection (GS) utilizes genome-wide marker information to predict an individual's breeding value and is suitable for improving complex traits controlled by multiple genes, such as aroma and flavor. GS can shorten the breeding cycle and improve the efficiency of seed selection. Recently, with the establishment of high-quality reference genomes and haplotype assembly of tea plants, haplotype breeding strategies have gradually emerged.
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