Differential Gene Expression Involved in Catechin Synthesis of Tea Leaves (Camellia sinensis) during Spring and Summer

In this study, the contents of polyphenols and catechins in the spring and summer shoots with one bud and two leaves of the tea cultivars Fuding Dabaicha, Baihaozao, Bixiangzao and Zhuyeqi were determined by the method specified in the national standard GB/T 8313-2018 and high-performance liquid chromatography (HPLC). The relative expression levels of catechin biosynthesis-related genes were determined by real-time polymerase chain reaction (real-time PCR). The results showed that for the four cultivars, the contents of EGC, ECG and EC in summer tea shoots were significantly higher than those in spring tea shoots (P < 0.01). The expression levels of the F3H and DFR genes tended to be higher in spring than in summer. Differential expression levels (|log₂ fold change|≥1) of the ANS, C4H, CHS, ANR, UGT84A and flavonoid 3’,5’-hydroxylase (F3’5’H) genes were found between spring tea shoots from Baihaozao and other samples, implying that the gene expression levels could be not only regulated by season, but also affected by cultivar. The relative expression level of F3’5’H was positively correlated with the content of EGCG, which is derived from the hydroxylation of flavanone at the 3’,4’, and 5’ positions of the B ring catalyzed by flavonoid 3’-hydroxylase (F3’H) and F3′5′H. Therefore, F3’5’H may be the key enzyme for EGCG synthesis.