Integrated metabolomic and transcriptomic analysis of Camellia sinensis var. pubilimba 'Rucheng Baimaocha' reveals distinct flavonoid and strictinin biosynthesis.
BACKGROUND 'Rucheng Baimaocha' (RCBMC) is a traditional tea landrace found in Hunan Province, China. Its morphological characteristics differ substantially from those of the other cultivars, featuring larger mature leaves with thicker cuticle layers. Both young buds and leaf undersides are densely covered in silvery-white trichomes, indicating that RCBMC has a distinct metabolite composition compared to other cultivars. To elucidate the metabolic profile differences and their underlying molecular mechanisms, we conducted an integrated metabolomic and transcriptomic analysis of RCBMC and representative cultivars. RESULTS Metabolomics revealed that RCBMC accumulated higher levels of non-epicatechins, such as catechin, catechin gallate, and gallocatechin gallate, and the ellagitannin strictinin, whereas flavonoid glycosides were significantly lower. Transcriptomics identified 11,775 differentially expressed genes with key shifts in the flavonoid pathway: upregulated LAR and downregulated ANS gene expression collectively redirected metabolic flux toward non-epicatechin synthesis. The downregulation of multiple UGT genes was correlated with reduced flavonoid glycoside levels. Weighted gene co-expression network analysis further identified transcription factors strongly associated with metabolite accumulation. Quantitative analysis of 607 medium- and small-leaf tea germplasms indicated that strictinin content was genetically influenced and seasonally regulated, with RCBMC exhibiting notably high levels. Correlation analysis identified candidate genes from the SCPL, CXE, and LAC families that are potentially involved in strictinin biosynthesis. CONCLUSIONS This study revealed a unique pattern of bioactive compound accumulation in RCBMC and provides valuable germplasm resources and genetic targets for breeding tea cultivars with enhanced functional components.