Title : UV-B irradiation differentially regulates phenylpropanoid and volatile terpenoid production in Camellia sinensis
Plants are known to protect themselves from UV-B damage by generating phenolic metabolites which absorbs UV-B light. Phenolics are extraordinarily abundant in Camellia sinensis and are considered, together with pleasant volatile terpenoids, as key flavour determinants in tea beverage. To understand UV-B induced alterations in tea flavor determinants (catechins and volatiles) for potential and practical improvement of green tea beverage flavor, in this study, UV-B irradiance (at 35 μW cm-2 for 2 hr) was applied to tea shoots and induced transcriptional and metabolic alterations specifically related to tea flavour metabolite production were examined Metabolite analyses clearly indicated that correlated changes in the abundance of catechins and some volatile terpenoids occurred due to the UV-B treatment. Eighteen genes in the volatile terpenoid pathway were enhanced and a linalool synthase gene was dramatically promoted, accompanied by induction of jasmonate biosynthesis and signaling pathways. Preliminary transcriptional analyses revealed that thirteen genes in the phenylpropanoid and flavonoid pathways were suppressed while six others in the lignin and anthocyanin pathways were enhanced. Comparison between the structural and regulatory genes suggested possibly negative roles for MYB4 on upstream phenylpropanoid pathways and positive roles for MYB3/308 on the lignin pathway. Our data indicated that the UV-B treatment applied in this study differentially regulated the phenylpropanoid, flavonoid and terpenoid pathways at transcriptional and metabolic levels in tea plants. These findings suggest a strong potential for UV-B treatment for tea flavour improvement.