Spatiotemporal variation characteristics of anthocyanins and catechins and key genes expression analysis of purple-leaf tea cultivars

Objective This study aimed to investigate spatiotemporal variation characteristics of anthocyanin and ca-techin in purple leaf tea plants and screen key genes of anthocyanin metabolism， so as to provide a scientific basis for elucidating the spatiotemporal distribution patterns of quality components in purple-leaf tea and utilizing of tea tree resources in Yunnan.Method Two tea plant cultivars， Zijuan （with purple buds and leaves） and Yunkang 10 （with green buds and leaves）， were used as research objects in this study. Tender shoots consisting of one bud and two leaves were collected from both cultivars respectively in March， April， May， July， September， and October in 2023. On May 8， shoots of Zijuan with one bud and six leaves were collected and separated into leaves according to their positions （labeled as ZJ-1L to ZJ-6L） corresponding to stem segments （ZJ-1S to ZJ-6S）. The contents of total anthocyanin and catechin monomers in collected samples were determined to analyze their dynamic variation patterns， followed by principal component analysis （PCA）， cluster analysis， and correlation analysis. The relative expression of key genes of anthocyanin metabolism in Zijuan were detected using real-time fluorescence quantitative PCR.Result The total anthocyanin content in new shoots of Zijuan tea plant was significantly higher than that of Yunkang 10 （P<0.05， the same below）. Across different sampling times， the total anthocyanin content in new shoots of Zijuan tea plant peaked on September 10^th （5.81 μmol/g）. At the same sampling time， sample ZJ-2L exhibited the highest total anthocyanin content （2.86 μmol/g）， which was significantly higher than that of other leaf positions and stem tissues. The average total catechin content in new shoots of Yun-kang 10 （210.94 mg/g） was 1.38 times that of Zijuan （153.08 mg/g）. Epigallocatechin gallate （EGCG） was the predominant catechin monomer in both tea cultivars. Correlation analysis revealed that total anthocyanin content and total catechin content in both cultivars were negatively correlated； however， the total anthocyanin content and total catechin content in Zijuan new shoots at the same sampling time had a highly significant positive correlation （P<0.01， the same below）. Cluster analysis results showed that， samples from the two tea cultivars， Zijuan and Yunkang 10， clustered respectively， and Zijuan samples collected at similar time points were clustered closer to each other. The leaf and stem tissue samples of Zijuan new shoots were clearly separated； ZJ-1L and ZJ-2L were clustered on the same branch， and they were further clustered with ZJ-1S； these three samples generally exhibited higher abundances in total anthocyanin and catechin monomers. When Zijuan new shoots grew maturer， their sample stems （ZJ-4S， ZJ-5S， and ZJ-6S） generally exhibited low abundances of these catechin monomers. Real-time fluorescence quantitative PCR analysis revealed that the relative expression of the MYB transcription factor gene （CsMYB75） in three Zijuan samples were significantly higher than those in Yunkang 10.Conclusion During the late summer to early autumn， a high content of total anthocyanin in one-bud-two-leaf shoots of the Zijuan is observed， and the catechin content in Zijuan tea plant is significantly lower than that in Yun-kang 10 （with green buds and leaves）. The sustained high expression of the CsMYB75 gene is identified as the key regulatory mechanism for the consistently high anthocyanin accumulation in Zijuan tea plant.