Abstract
There were several high concentrations of flavonoid components in tea leaves that present health benefits. A novel purple-leaf tea variety, ‘Mooma1’, was obtained from the natural hybrid population of Longjing 43 variety. The buds and young leaves of ‘Mooma1’ were displayed in bright red. HPLC and LC-MS analysis showed that anthocyanins and O-Glycosylated flavonols were remarkably accumulated in the leaves of ‘Mooma1’, while the total amount of catechins in purple-leaf leaves was slightly decreased compared with the control. A R2R3-MYB transcription factor (CsMYB6A) and a novel UGT gene (CsUGT72AM1), that were highly expressed in purple leaf were isolated and identified by transcriptome sequencing. The over-expression of transgenic tobacco confirmed that CsMYB6A can activate the expression of flavonoid-related structural genes, especially CHS and 3GT, controlling the accumulation of anthocyanins in the leaf of transgenic tobacco. Enzymatic assays in vitro confirmed that CsUGT72AM1 has catalytic activity as a flavonol 3-O-glucosyltransferase, and displayed broad substrate specificity. The results were useful for further elucidating the molecular mechanisms of the flavonoid metabolic fluxes in the tea plant.
Highlights
Flavonoids are derived from the phenylpropanoid metabolic pathway, in which cinnamoyl-(C6-C3) is combined to yield the backbone with three malonyl-CoA units
A new purple-leaf tea variety ‘Mooma 1’ was reported in this paper, which was selected from the natural hybrid population of ‘Longjing 43’
The buds and young leaves of ‘Mooma 1’ displayed bright red color, where the anthocyanins were remarkably accumulated in the palisade mesophyll tissue, but were absent in the epidermis
Summary
Flavonoids are derived from the phenylpropanoid metabolic pathway, in which cinnamoyl-(C6-C3) is combined to yield the backbone with three malonyl-CoA units. Genes involved in these flavonoid pathways are evident through model species. In this pathway, the functional enzymes have been classified into two groups, early-biosynthetic enzymes are required for the synthesis of flavonoids, and late-biosynthetic enzymes are used for the synthesis of anthocyanins, catechins, and flavonols[18,19,20]. Numerous studies have suggested that the fluxion of this pathway is tightly regulated by the transcription factor complex MYB-bHLH-WD40(MBW). Specific combinations of R2R3-MYB transcription factor with bHLH and WD40 regulate specific pathways of anthocyanin or PA biosynthesis[4,24]. The component analysis, quantitative reverse transcriptase PCR (qRT-PCR) analysis, and the over-expression of transgenic tobacco confirmed that CsMYB6A can activate the expression of flavonoid-related structural genes controlling the accumulation of anthocyanins and flavonols in the leaves. The results are useful to further elucidate the molecular mechanisms of the flavonoid metabolic fluxes in the tea plant
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