Ambient Ultraviolet B Signal Modulates Tea Flavor Characteristics via Shifting a Metabolic Flux in Flavonoid Biosynthesis

Tea leaves contain an extraordinarily high level of flavonoids that contribute to tea health benefits and flavor characteristics, but the regulatory mechanism of ambient ultraviolet B (UV-B) on tea flavonoid enrichment remains unclear. Here, we report that ambient UV-B modulates tea quality by inducing a metabolic flux in flavonoid biosynthesis. UV-B absence decreased bitter- and astringent-tasting flavonol glycosides (kaempferol-7-O-glucoside, myricetin-3-O-glucoside, and quercetin-7-O-glucoside) but increased non-galloylated catechins. Conversely, supplementary UV-B increased flavonols and decreased catechins in tea leaves. These responses were achieved via CsHY5, which mediates the UV-B-induced MYB12 activation and binds to the promoters of flavonoid biosynthetic genes (CsFLS, CsLARa, and CsDFRa), leading to flavonoid changes. Transcriptomic data indicated that UV-B-induced tea flavonoid regulation is responsive to multiple biotic and abiotic environmental stresses. These findings improve our understanding of light-regulated tea astringency and bitterness underlying shading effects and seasonal light changes and provide novel insights into tea cultivation management and processing.