Tea plants (Camellia sinensis) are used to produce one of the most important beverages worldwide. The nutritional value and healthful properties of tea are closely related to the large amounts of three major characteristic constituents including polyphenols (mainly catechins), theanine and caffeine. Although oil tea (Camellia oleifera) belongs to the genus Camellia, this plant lacks these three characteristic constituents. Comparative analysis of tea and oil tea via RNA-Seq would help uncover the genetic components underlying the biosynthesis of characteristic metabolites in tea. We found that 3,787 and 3,359 bud genes, as well as 4,042 and 3,302 leaf genes, were up-regulated in tea and oil tea, respectively. High-performance liquid chromatography (HPLC) analysis revealed high levels of all types of catechins, theanine and caffeine in tea compared to those in oil tea. Activation of the genes involved in the biosynthesis of these characteristic compounds was detected by RNA-Seq analysis. In particular, genes encoding enzymes involved in flavonoid, theanine and caffeine pathways exhibited considerably different expression levels in tea compared to oil tea, which were also confirmed by quantitative RT-PCR (qRT-PCR). We assembled 81,826 and 78,863 unigenes for tea and oil tea, respectively, based on their differences at the transcriptomic level. A potential connection was observed between gene expression and content variation for catechins, theanine and caffeine in tea and oil tea. The results demonstrated that the metabolism was activated during the accumulation of characteristic metabolites in tea, which were present at low levels in oil tea. From the molecular biological perspective, our comparison of the transcriptomes and related metabolites revealed differential regulatory mechanisms underlying secondary metabolic pathways in tea versus oil tea.

For a better understanding terpenoid volatile production in Camellia sinensis, global terpenoid synthase gene (TPS) transcription analysis was conducted based on transcriptomic data combined with terpenoid metabolic profiling under different abiotic stress conditions. Totally 80 TPS-like genes were identified. Twenty-three CsTPS genes possessed a complete coding sequence and most likely were functional. The remaining 57 in the currently available database lack essential gene structure or full-length transcripts. Distinct tempo-spatial expression patterns of CsTPS genes were found in tea plants. 17 genes were substantially expressed in all the tested organs with a few exceptions. The other 17 were predominantly expressed in leaves whereas additional eight were primarily expressed in flowers. Under the treatments of cold acclimation, salt and polyethylene glycol, CsTPS67, -69 and -71 were all suppressed and the inhibited expression of many others were found in multiple stress treatments. However, methyl jasmonate resulted in the enhanced expression of the majority of CsTPS genes. These transcription data were largely validated using qPCR. Moreover, volatile terpenoid profiling with leaves, flowers and stress-treated plants revealed a general association between the abundances of mono- and sesqui-terpenoids and some CsTPS genes. These results provide vital information for future studies on CsTPS regulation of terpenoid biosynthesis.