Comparative Transcriptome Analysis Reveals Putative Genes Responsible for High Theacrine Content in Kucha ( Camellia kucha (Chang et Wang) Chang)

The purine alkaloid theacrine, synthesized in a high amount in Kucha (Camellia kucha (Chang et Wang) Chang), has shown multiple pharmacological effects such as anti-depression, dehydration and hypnotic activities. It is critical to better understand the theacrine metabolism at the molecular level for future breeding programs. To identify the putative genes involved in theacrine biosynthesis, we carried out comparative transcriptome analysis between Kucha (Kucha-6 and Kucha-11) and conventional varieties (Yinghong 9 and Qingxin 1). HPLC showed that Kucha synthesized more than 27-fold theacrine in comparison to conventional varieties. A total of ~ 671.61 million high quality clean reads were yielded, and 71.42 ~ 76.87% of these were aligned to the reference genome for each library. We identified 19,095 differentially expressed genes (DEGs) by a pairwise approach, among which 1,142 common DEGs between Kucha and conventional varieties were screened. Functional annotation allowed the identified of 20 oxidoreductase (OR) genes and seven methyltransferase (MT) genes with enhanced expression in Kucha, which might be associated with theacrine diversity in the examined materials. Particularly, two N-methyltransferase-encoding genes (TEA010054 and TEA022559) may catalyze the final methylation step during theacrine synthesis in Kucha. The information generated will be helpful in identifying candidate genes and breeding tea plant with high theacrine content.