咖啡碱，即1，3，7-三甲基黄嘌呤，是茶、马黛、可可、咖啡中都存在的一种次生代谢物质，作为嘌呤碱，它主要在幼叶、子叶、种子和果实中积累，在茶叶中，咖啡碱可以占到2%-5%。为了进一步明晰咖啡碱在山茶属植物中的代谢机制，作者以低咖啡碱的厚轴茶资源LCT1和LCT2、正常咖啡碱的茶树品种‘舒茶早’和高咖啡碱的茶树品种‘云抗43’为材料，利用RNA-seq和LC-MS技术对它们的转录组特性及嘌呤碱组分与含量进行分析，同时利用N15标记的咖啡碱示踪法进行咖啡碱代谢追踪。结果发现咖啡碱的含量与相关基因的表达显著相关，并发现了一条咖啡碱降解成可可碱的代谢途径。

Abstract

Caffeine is a crucial secondary metabolic product in tea plants. Although the presence of caffeine in tea plants has been identified, the molecular mechanisms regulating relevant caffeine metabolism remain unclear. To elucidate the caffeine biosynthesis and catabolism in Camellia plants, fresh, germinated leaves from four Camellia plants with low (2), normal (1) and high (1) caffeine concentrations, namely low-caffeine tea 1 (LCT1, Camellia crassicolumna), low-caffeine tea 2 (LCT2, C. crassicolumna), Shuchazao (SCZ, C. sinensis) and Yunkang 43 (YK43, C. sinensis) were used in this research. Transcriptome and purine alkaloids analyses of these Camellia leaves were performed using RNA-Seq and liquid chromatography-mass spectrometry (LC-MS). Moreover, 15N-caffeine tracing was performed to determine the metabolic fate of caffeine in leaves of these plants. Caffeine content was correlated with related genes expression levels, and a quantitative real-time (qRT) PCR analysis of specific genes showed a consistent tendency with the obtained transcriptomic analysis. Based on the results of stable isotope-labelled tracer experiments, we discovered a degradation pathway of caffeine to theobromine. These findings could assist researchers in understanding the caffeine-related mechanisms in Camellia plants containing low, normal, and high caffeine content and be applied to caffeine regulation and breeding improvement in future research.