Metabolomics and Transcriptomics Analyses Reveal Nitrogen Influences on the Accumulation of Flavonoids and Amino Acids in Young Shoots of Tea Plant (Camellia sinensis L.) Associated with Tea Flavor

Tea-specialized metabolites contribute to rich flavors and healthy function of tea. Their accumulation patterns and underlying regulatory mechanism are significantly different under different nitrogen (N) conditions during adaptation stage. Here, we find that flavonoids associated with tea flavor are dominated by different metabolic and transcriptional responses among the four N conditions (N-deficiency, nitrate, ammonia, and nitric oxide). Nitrogen-deficiency tea plants accumulate diverse flavonoids, corresponding with higher expression of hub genes including F3H, FNS, UFGT, bHLH3S, and bHLH36. Compared with N-deficiency, N-supply tea plants significantly increase proline, glutamine, and theanine, which are also associated with tea flavor, especially under NH4+-supply. As NH4+-tolerant species, tea plant exploits the adaptive strategy by substantial accumulation of amino acids including theanine to adapt excess NH4+, which attributes to, at least in part, efficient N transport and assimilation, and active protein degradation. A distinct divergence of N reallocation in young shoots of tea plant under different N sources contributes to diverse tea flavor.