Abstract
The R2R3-MYB transcription factor (TF) family regulates metabolism of phenylpropanoids in various plant lineages. Species-expanded or specific MYB TFs may regulate species-specific metabolite biosynthesis including phenylpropanoid-derived bioactive products. Camellia sinensis produces an abundance of specialized metabolites, which makes it an excellent model for digging into the genetic regulation of plant-specific metabolite biosynthesis. The most abundant health-promoting metabolites in tea are galloylated catechins, and the most bioactive of the galloylated catechins, epigallocatechin gallate (EGCG), is specifically relative abundant in C. sinensis. However, the transcriptional regulation of galloylated catechin biosynthesis remains elusive. This study mined the R2R3-MYB TFs associated with galloylated catechin biosynthesis in C. sinensis. A total of 118 R2R3-MYB proteins, classified into 38 subgroups, were identified. R2R3-MYB subgroups specific to or expanded in C. sinensis were hypothesized to be essential to evolutionary diversification of tea-specialized metabolites. Notably, nine of these R2R3-MYB genes were expressed preferentially in apical buds (ABs) and young leaves, exactly where galloylated catechins accumulate. Three putative R2R3-MYB genes displayed strong correlation with key galloylated catechin biosynthesis genes, suggesting a role in regulating biosynthesis of epicatechin gallate (ECG) and EGCG. Overall, this study paves the way to reveal the transcriptional regulation of galloylated catechins in C. sinensis.
Highlights
Tea from Camellia sinensis, along with coffee and cocoa, is one of the world’s three major non-alcoholic beverages
As it is believed that genes which clustered together were considered to be in the same subgroup, and A. thaliana is, by far, the species for which the R2R3-MYB genes have been most extensively investigated, the 38 subgroups were classified by taking into account the topology of the tree and the bootstrap values (Figure 1 and Supplementary Table 3) and were named according to the classification of A. thaliana
This study has laid a theoretical framework and valuable foundation for the future work, as we have provided a preliminarily evidence for illuminating that the high accumulation of galloylated catechins in C. sinensis are likely to be caused by the expanded R2R3-MYB transcription factors (TFs)
Summary
Tea from Camellia sinensis, along with coffee and cocoa, is one of the world’s three major non-alcoholic beverages. The tea plant (C. sinensis) is rich in characteristic metabolites, such as polyphenols, amino acids, caffeine, and terpenes, that significantly contribute to its pleasant flavors and industrial and medical value (Wei et al, 2018). Among them, galloylated catechins ECG and EGCG are relatively abundant in tea plants and account for more than 80% of total catechins (Kim et al, 2004; Liu et al, 2012). EGCG, the most specific accumulated metabolite that quantitatively differentiated from the other plants, is the major bioactive component conferring the many health benefits of tea – it is anti-carcinogenic (Ahmad et al, 2000), anti-oxidative (Heim et al, 2002), anti-bacterial and anti-inflammatory (Taguri et al, 2004), and it prevents cardiovascular and cerebrovascular diseases (Yu X. et al, 2020). EGCG is widely used in food production on account of its strong antioxidative capacity (Nikoo et al, 2018)
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