Integrated metabolomic and transcriptomic analyses provide new perspectives into the discoloration of hawk tea tender...

In Southwest China, the spring-colored leaves of the Lauraceae plant Litsea coreana, often known as hawk tea, produce a traditional beverage with cultural and economic significance. Its immature leaves are generally red or green coloration, transitioning to common green as they mature. The possible quality benefits of high-anthocyanin tea cultivars with unusual leaf hues have recently drawn attention. It is important from a scientific and practical standpoint to clarify the metabolism and manufacture of pigments in hawk tea leaves that have different starting hues during the developmental stages.

This study applied both targeted metabolomics and transcriptomics to investigate the metabolite accumulation and molecular mechanisms in red and green hawk tea tender leaves across three developmental stages. Metabolomic profiling revealed that cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, and pelargonidin-3-O-glucoside specifically accumulated in red tender leaves (2.44 to 4.59 Log₂FC higher than in green leaves), with levels progressively decreasing during the red-to-green transition. Transcriptomic analysis demonstrated that key late biosynthetic genes (ANR, 3GT) were consistently upregulated in red leaves and strongly correlated with anthocyanin content. In contrast, lignin pathway genes (HCT, CCOAMT) were downregulated in red leaves, suggesting that carbon flux is preferentially directed toward anthocyanin rather than lignin synthesis in red leaves. Additionally, co-expression network analysis further delineated nine candidate transcription factors (three MYB, two bHLH, three C2C2 zinc finger proteins, and one GRAS) that exhibited coordinated expression patterns with pigment biosynthetic genes, were predicted to directly or indirectly regulate anthocyanin biosynthesis in response to endogenous substances such as nitrogen, hormones, and sugars.

Our findings identify that red leaf color in L. coreana is driven by anthocyanin accumulation, which is achieved through a metabolic shift that directs carbon flux away from lignin and toward anthocyanin biosynthesis. This shift is likely regulated by a set of nine transcription factors. These findings provide concrete targets for breeding high-anthocyanin hawk tea varieties.