## 3 Discussion
Isopenoids synthesized via MVA and MEP pathways are controlled by independent regulatory networks with restricted connectivity [45]. HMGR and DXS are two rate-limiting enzymes in the MVA pathway [46] and the MEP pathway [47]. In the transcriptomes of the linalool- and borneol-chemotypes of _C. camphora_, 30 unigenes, which were highly homologous to 14 known enzymes, were annotated in the MVA and MEP pathways of terpene skeleton biosynthesis in the borneol, and high transcriptome expression levels were shown in both chemotypes [13]. In of _C. porrectum_, there were 21 unigenes encoding TPS in the eucalypt chemotype and linalool chemotype comparative group, 5 monoterpene synthase unigenes upregulated in the eucalypt chemotype, and 2 monoterpene synthase unigenes upregulated in the lanalool chemotype. There were 22 unigenes encoding TPS in the camphor chemotype and eucalypt chemotype comparative group, 3 upregulated monoterpene synthase unigenes in the camphor chemotype, and 6 upregulated monoterpene synthase unigenes in the eucalypt chemotype. There were 18 unigenes encoding TPS in the camphor chemotype and linalool chemotype comparative group, 2 upregulated monoterpene synthase unigenes in the chemotype camphor, and 3 upregulated monoterpene synthase unigenes with upregulated expression in linalool chemotype. These results indicate that there may be differences in the gene expression patterns for the regulation and formation of monoterpenoids among different chemotypes. The MEP pathway provides precursors for the synthesis of monoterpenes and diterpen in plastids, while sesquiterpenenes are derived from precursors of the MVA pathway in the cytoplasm [45]. The unigene expression level of the MEP pathway was higher than that of the MVA pathway indicating the abundance of monoterpenes. Crosstalk between these two different terpene skeleton pathways has been documented, and the relative contribution of each pathway to terpene biosynthesis remains uncertain. TPS genes is responsible for the synthesis of diverse terpenoids molecules from two isomeric isoprene precursors. The phylogenetic tree of _C. porrectum_ with the characterized TPS proteins is divided into seven clades, with a majority expansion of TPS-a and TPS-b clades, indicating gene family expansion is correlated with mono- and sesquiterpene diversity. Monoterpenes are the principal components of many member leaf extracts of _Cinnamoun_ species, such as _Cinnamoun osmophloeum_[26], _Cinnamoun kanehirae_[48] and _Cinnamoun camphora_[13]. In this paper, 33 components were identified in the essential oil from leaf tissue of the eucalypt chemotype, linalool chemotype and camphor chemotype of _C. porrectum_. Analysis of the components showed that the essential oils isolated from the three chemotypes were mainly composed of monoterpenes, including 20 monoterpenoids, basically complying with the study results in _C. camphora_[13]; however, there were significant differences in the varieties and contents of monoterpenoids among the three chemical types. The content of linalool in the linalool chemotype was 77.58%-87.88%, but the linalool content was very low in the other two chemotypes. The content of eucalyptptol in the eucalyptt chemotype was 34.48-35.63%, but the eucalyptt content was extremely low in the other two chemotypes. Notably, the monoterenoid content of the camphor chemotype was almost pure camphor, but camphor was absent or present in a small amount in the other two chemotypes. The difference in the contents of the three main monoterrepenoids (linalool, eucalyptt and camphor) in the three chemotypes of _C. porctum_ greatly coincided with the differential expression of monoterpene synthase genes, such as _CpTPS1_, _CpTPS3_, _CpTPS4_, _CpTPS5_ and _CpTPS9_, among the three different chemotypes. Presumably, the _CpTPS4_ gene is highly likely to affect the synthesis oflinalool in _C. porctum_ leaf tissue, the _CpTPS3_, _CpTPS5_ and _CpTPS9_ genes affect the synthesis of eucalyptt, and the _CpTPS1_, gene is related to the synthesis of camphor.