Effects of Photoperiod on Anthocyanin Biosynthesis-Related Gene Expression and Enzymatic Activity in Purple-Leaf Tea Plants (Camellia sinensis)

Tea is a vital economic crop in China, with many anthocyanin-rich cultivars having been bred. Photoperiod is an important environmental factor that regulates anthocyanin production in plants. Nonetheless, the precise mechanisms by which photoperiod affects anthocyanin biosynthesis in tea plants remain unclear. In this study, the purple-leaf cultivar <i>Camellia sinensis</i> 'Ziyan' was exposed to three different photoperiods: 8 h/16 h (light/dark, short-day, SD), 14 h/10 h (light/dark, medium-day, MD), and 20 h/4 h (light/dark, long-day, LD). A comprehensive analytical approach, including transcriptomics, enzymology, and quantitative anthocyanin analysis, was used to uncover the molecular and biochemical processes regulating anthocyanin synthesis in purple-leaf tea plants grown under varying photoperiods. The results showed that the delphinidin, cyanidin, pelargonidin, and total anthocyanin contents in the long-day treatment were 178.10%, 92.37%, 50.40%, and 148.76% higher, respectively, than those in the short-day treatment. Under long-day conditions, all structural genes associated with anthocyanin synthesis were upregulated, and enzymatic activities related to anthocyanin synthesis were significantly increased. Furthermore, the regulatory genes (<i>MYB</i>1, <i>MYB</i>73, <i>MYB</i>111, <i>MYB</i>48, <i>MYB</i>75, <i>MYB</i>113, <i>MYB</i>5, <i>MYB</i>12, <i>MYB</i>5a, <i>MYB</i>5b, and <i>WRKY</i>41) were differentially expressed under short- and long-day treatments. These findings suggest that extended photoperiods activate the expression of structural genes through gene regulation and enhancement of enzymatic activity, thereby facilitating anthocyanin biosynthesis. This study provides novel insights into the photoperiodic regulation of anthocyanin biosynthesis in tea plants.