Transcriptome Analysis Reveals The Accumulation Mechanism Of Anthocyanins In ’Zijuan’ Tea (Camellia Sinensis Var. Asssamica (Masters) Kitamura) Leaves

Anthocyaninwith the characteristics of safety, non-toxic, natural color, rich in resources is a kind of water soluble natural pigmentand has great potential in food, cosmetic, medicine, landscape environment. Anthocyanin biosynthesis in herbaceous plants has been studied widely, but the mechanism of anthocyanin accumulation in ’Zijuan’tea remains unclear.In this study, the leaf transcriptome of’Zijuan’tea was analyzed at the purple and green stages by using the Illumina HiSeq 2500 platform. 107,984 transcripts and 34,685 Unigenes were received.2,250 differentially expressed genes were screened, among which 1,270 genes were up-regulated and 980 were down-regulated.Anthocyanin biosynthesis, carbohydrate metabolism and brassinosteroids biosynthesiswere significantly enriched through the KEGG metabolic pathway analysis of differentially expressed unigenes (DEGs). Several genes involved inanthocyanin biosynthesis were identified, such as PAL, Cinnamate acid 4-hydroxylase (C4H),4-coumarate-CoA ligase (4CL), Flavonoid 3’,5’-hydroxylase (F3’5’H), CHS, DFR, ANS, UFGT, and ATP-binding cassette (ABC). The up-regulation of these genes maypromote the biosynthesisand transport of anthocyanins.In addition,9 genes involved in carbohydrate metabolism were also identified. The upregulated sucrose synthase gene in the purple leaves may provide hexoses and UDP-glucose for anthocyanin synthesis. The genes encoding the corresponding enzymes in the glycolysis pathway were upregulated, whereas those genes encoding the enzymes in the TCA cycle showed no significant changes. Increased acetyl-CoA may contribute to anthocyanin accumulation through the upregulated cytosolic acetyl-coenzyme A carboxylase (ACCase) gene in the purple leaves of ’Zijuan’ tea, indicating that glycolysis may provide more intermediates as subtracts for promoting anthocyanin accumulation.Finally, three genes involved in brassinosteroids synthesis had also been identified, includingsqualene epoxidase (SQE), cycloartenol synthase (CAS) and sterol-C-24-methyltranferase (SMT1).The up-regulation of the three genes can provide more precursors for the synthesis ofbrassinosteroids, which is beneficial to the synthesis of anthocyanin.The physiological and qRT-PCR results were consistent with the RNAseq data.The results of this study laid a theoretical and research foundation for the breeding of good quality, high anthocyanin, good stability of the purple bud tea tree by transgenic technology in the future.