A Correlation Study of Caffeine Content with Theobromine Content, cSNPs, and Transcriptional Expression of Three Genes in Tea Plants

ABSTRACT Caffeine is an important secondary metabolite of tea plants whose content is affected by multiple factors during its synthesis. In the present study, a series of experiments on different tea cultivars were performed to investigate the following factors that influence the ratio of caffeine content to theobromine content, coding single‐nucleotide polymorphisms (cSNPs), and expression levels of three key enzyme genes ( TCS1 , TIDH , and sAMS ). The results revealed a significantly positive correlation with the caffeine and theobromine contents of different tea cultivars. There were 7, 8, and 7 cSNPs in the coding sequences of TCS1 , TIDH , and sAMS , respectively. Among them, the TCS1 A995C, TIDH T573A, and sAMS C393T cSNP sites were significantly associated with the caffeine content. Gene expression was detected by the quantitative real‐time polymerase chain reaction (qRT‐PCR) method, and it suggested a significant association of TCS1 expression with caffeine content but not with theobromine content. TIDH and sAMS expression levels had no significant association with either caffeine or theobromine content. Therefore, it could be concluded from the study findings that the following three factors had a significant influence on the biosynthesis of caffeine in tea plants: the precursor theobromine content; SNPs in TCS1 , TIDH , and sAMS in the coding region; and TCS1 expression level.