Comparative transcriptomic analysis unveils the deep phylogeny and secondary metabolite evolution of 116 Camellia plants.

Camellia plants include more than 200 species of great diversity and immense economic, ornamental, and cultural values. We sequenced the transcriptomes of 116 Camellia plants from almost all sections of the genus Camellia. We constructed a pan-transcriptome of Camellia plants with 89 394 gene families and then resolved the phylogeny of genus Camellia based on 405 high-quality low-copy core genes. Most of the inferred relationships are well supported by multiple nuclear gene trees and morphological traits. We provide strong evidence that Camellia plants shared a recent whole genome duplication event, followed by large expansions of transcription factor families associated with stress resistance and secondary metabolism. Secondary metabolites, particularly those associated with tea quality such as catechins and caffeine, were preferentially heavily accumulated in the Camellia plants from section Thea. We thoroughly examined the expression patterns of hundreds of genes associated with tea quality, and found that some of them exhibited significantly high expression and correlations with secondary metabolite accumulations in Thea species. We also released a web-accessible database for efficient retrieval of Camellia transcriptomes. The reported transcriptome sequences and obtained novel findings will facilitate the efficient conservation and utilization of Camellia germplasm towards a breeding program for cultivated tea, camellia, and oil-tea plants.

Caffeine Content and Related Gene Expression: Novel Insight into Caffeine Metabolism in Camellia Plants Containing Low, Normal, and High Caffeine Concentrations.

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. For the elucidation of 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 gene expression levels, and a quantitative real-time (qRT) PCR analysis of specific genes showed a consistent tendency with the obtained transcriptomic analysis. On the basis of the results of stable isotope-labeled 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.