CsMADS Negatively Regulates the Theobromine Content of Leaves in Tea Plants

Theobromine is a significant purine alkaloid found in tea plants, known for its various bioactive functions in humans. While the metabolic pathway for purine alkaloids, particularly involving the methyltransferase CsTCS1, has been largely understood, information regarding the upstream regulatory network of theobromine remains limited. In this study, we collected transcriptome data from tea plants exhibiting different levels of purine alkaloids and applied weighted gene co-expression network analysis (WGCNA) to identify the upstream regulatory network modules associated with each purine alkaloid. The module labeled MEred was discovered as one of the negative regulatory network modules affecting theobromine, with the gene CsMADS identified as a hub gene within this module. To investigate the role of CsMADS in theobromine accumulation, we examined the concentrations of purine alkaloids and the expression patterns of related genes in the CsMADS-silenced tea plants. Results showed that theobromine levels increased in the tender leaves of CsMADS-silenced tea plants, while the expression level of CsTCS1 decreased in these plants. Meanwhile, CsMADS did not influence mechanical harvesting-related traits such as leaf droopiness or leaf tip expansion. In summary, CsMADS negatively regulates the theobromine content in tea leaves without adversely affecting mechanical harvesting capabilities.