茶树咖啡碱生物合成路径中，腺嘌呤被认为是最有效的前体，其代谢途径为A（腺嘌呤）→AMP (单磷酸腺苷)→IMP(次黄嘌呤核苷单磷酸)→XMP（黄嘌呤核苷单磷酸）→XR（黄嘌呤核苷）→7-MXR（7-甲基黄嘌呤核苷）→7-MX（7-甲基黄嘌呤）→Tb（可可碱）→Cf（咖啡碱）。以AMP为原料合成咖啡碱的过程称为从头合成，是茶树体内咖啡碱的主要合成途径。从XR到Cf合成途径已比较清晰，但以AMP为原料的咖啡碱从头合成研究至今没有突破。申请项目通过在真核细胞中对茶树咖啡碱从头合成过程中关键酶：AMP脱氨酶、IMP脱氢酶、S-腺苷甲硫氨酸合成酶、黄嘌呤核苷甲基转移酶和咖啡碱合成酶的基因进行组合表达，实现咖啡碱的从头合成。预期结果将深入揭示茶树中从嘌呤核苷酸转化形成咖啡碱的代谢途径，有助于深入理解高等植物核酸与生物碱代谢之间的关系，为低生物碱茶树品种选育提供理论依据，为体外规模化生产咖啡碱提供参考。

Adenine, is considered as the most effective precursor substance in the caffeine biosynthetic pathway of Camellia sinensis, whose and the metabolic pathway is list as follows: Adenine→ AMP→ IMP→ XMP→ xanthosine→ 7-methylxanthosine→ 7-methylxanthine→ theobromine→ caffeine. The pathway with AMP as the starting material is called de novo biosynthesis of caffeine and regarded as the main route of caffeine biosynthesis in Camellia sinensis. Although the biosynthesis from xanthosine to caffeine has almost been clear, while the de novo biosynthetic pathway with AMP as the starting material is still unknown up to present. The current project is to reveal the do nevo biosynthesis from AMP to caffeine by the co-expression of the key genes in the eukaryotic cell system. These genes isolated from Camellia sinensis include AMP deaminase, IMP dehydrogenase (TIDH), S-adenosyl-L-methionine synthetase (sAMS), xanthosine methyltransferase (XMT) and caffeine synthase (TCS). Results will not only comprehensively reveal the biosynthetic pathway step by step from purine nucleotides to caffeine in tea plant, but also help us profoundly understand the relationship between nucleic acid metabolism and alkaloid metabolism in higher plants. Meanwhile the obtained research results will provide a theoretical evidence for the molecular breeding of lower-alkaloid tea plants and reference for production of caffeine in vitro in large-scale.