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.
Seasonal greening is a crucial survival strategy for albino tea cultivars, during which dysfunctional chloroplasts recover and chlorophyll biosynthesis increases in albino leaves. However, the regulatory mechanisms of seasonal greening in albino tea plants remain unclear. Here, we report that CsRVE1, a nuclear-located Myb-like transcription factor, can positively modulate the seasonal greening of albino Camellia sinensis cv. Huangkui leaves by activating the expression of genes involved in light harvesting and chlorophyll biosynthesis. The transcriptional expression of CsRVE1 increased during seasonal greening and was tightly correlated with increases in the expression of genes involved in light harvesting (CsLhcb) and chlorophyll biosynthesis (CsCHLH, CsHEMA1, CsCLH2, and CsCAO). In vivo and in vitro molecular analyses showed that CsRVE1 can directly bind to the promoters of CsLhcb, CsCHLH, and CsPORA, eventually leading to chlorophyll accumulation in tea leaves. Furthermore, transient suppression of CsRVE1 in tea leaves led to a decrease in target gene expression. In contrast, overexpression of CsRVE1 in Arabidopsis led to chlorophyll increases and activation of AtLhcb, AtPORA, AtCHLH, etc. These results identify CsRVE1 as an important promoter of seasonal greening that functions by regulating genes involved in chlorophyll biosynthesis in albino tea plants and shed new light on the regulatory mechanisms of leaf phenotypes in plants.
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