Transformation of catechins into theaflavins by upregulation of CsPPO3 in preharvest tea (Camellia sinensis) leaves exposed to shading treatment

Catechins and theaflavins are important metabolites contributing to tea function and quality. Catechins are known to transform into theaflavins during the tea manufacturing process, but the same transformation in preharvest tea leaves is unknown. Herein, we determined that shade treatment (dark), an agronomic practise widely used in tea cultivation, reduced the contents of most catechins, but increased the theaflavin contents, in preharvest tea leaves (cv. Yinghong No.9). This was attributed to the activation of polyphenoloxidase (PPO) activity in darkness. Furthermore, CsPPO3 was highly expressed under darkness, and thus CsPPO3 had been cloned, sequenced, and characterization. The CsPPO3 recombinant protein exhibited PPO function. Furthermore, shade treatment also reduced the catechin contents and increased the theaflavin contents in Yabukita and Hoshinomidori, suggesting that this phenomenon might not be specific to certain tea cultivars. This information will aid in understanding of theaflavin formation and its response to environmental factors at the preharvest tea stage.