Transcriptomic analysis identifies differentially expressed genes in purple tender shoots and green mature leaves of Zijuan tea

Purple shoots of tea germplasm Zijuan (Camellia sinensis var. asssamica) have high anthocyanin content and gradually turn green with continued growth and development. To uncover the mechanism of this colour change, we performed transcriptome analysis to identify differentially expressed genes (DEGs). A total of 18 328 DEGs were identified in purple tender shoots of Zijuan (ZJP) compared with mature green leaves of Zijuan (ZJG). These included 85 DEGs associated with phenylpropanoid biosynthesis, 30 DEGs associated with flavonoid biosynthesis, and 3 DEGs involved in flavone and flavonol biosynthesis. We detected higher expression in ZJP than in ZJG of genes encoding the following key enzymes regulating anthocyanin biosynthesis and their corresponding metabolites: chalcone synthase (CHS), anthocyanidin synthase (ANS), anthocyanidin reductase (ANR), adenosine triphosphate (ATP)-binding cassette (ABC) transporters, bifunctional 3-dehydroquinate dehydratase (DHQ), chorismate mutase (CM), cinnamoyl-CoA reductase 1 (CCR), and cinnamyl alcohol dehydrogenase (CAD). In addition, upregulated expression of carbohydrate metabolism, glycolysis pathway, sucrose metabolism, and pyruvate metabolism suggested that glycolysis and upregulation of the sucrose synthase (SUS) gene may provide more intermediates as substrates for promoting anthocyanin accumulation in ZJP. Moreover, DEGs involved in anthocyanin biosynthesis, including phenylalanine ammonialyase (PAL), cinnamate acid 4-hydroxylase (C4H), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonol synthase (FLS), ANR, ANS, CHS, and flavonoid 3',5'-hydroxylase (F3'5'H) were significantly (P < 0.01) correlated with the contents of anthocyanin components such as cyanidin (Cy), delphinidin (Dp), peonidin (Pn), petunidin (Pt), and malvidin (Mv). The above results suggested that these upregulated DEGs may contribute to anthocyanin accumulation in ZJP and may play important roles in the colour changes in Zijuan tea. This research provided a foundation for clarifying the mechanisms underlying colour changes in Zijuan tea.