## 3 Discussion  
At present, research on the _Cinnamomum camphora_ transcriptome has mainly been based on cost-effective next-generation RNA sequencing [13]. However, because of the short read length of this method, it is difficult to obtain an accurate full-length sequence using next-generation RNA sequencing without a reference genome [42]. PacBio Iso-Seq, the most popular application of third-generation sequencing, has proven useful for accurately characterizing the diverse landscape of isoforms, as this method can obtain full-length transcripts [43]. Using the PacBio Iso-Seq method, this study provided the first comprehensive set of full-length isoforms in _C. porrectum_. After eliminating redundancy, a total of 104/062 transcripts were obtained, with a total of 306,337,921 bp, an average sequence length of 2944 bp, and an N50 length of 5449 bp. Based on these highly accurate transcripts, a total of 104,062 transcripts were successfully annotated by at least one of seven known functional protein databases (NR, NT, GO, KCG, KEGG, SwissProt, Interpro). Furthermore, 104,062 genes were involved in a metabolic pathway of 19 KEGG pathway databases, and 1495 unigenes were found to be enriched in pathways of terpenoid and polyketide metabolism. These results indicate that PacBio transcriptome sequencing has a high ability to generate full-length transcript sequence information, providing an important reference for genome annotation and gene function analysis. In recent years, genes associated with terpene biosynthesis have been studied extensively in different plants. Lauraceous plants are rich in terpenoids, and several genes involved in the biosynthesis of terpenoids have been successfully identified, and their functions have been explored [26; 29]. Three TPS genes encoding monoterpene synthases were isolated in _Litsea cubbea: LcTPS1_, which converts geranyl diphosphate to trans-ocimene, _LcTPS2_, which converts geranyl diphosphate to \(\alpha\)-thujene,  
Figure 7: qRT-PCR validation of selected genes in five chemotypes of C. porrectum. The five chemotypes are the linalool-, eucalyptpol-, camphor-, nerolidol and citral-type. Relative expression levels were estimated from the threshold of the PCR cycle using the Delta CT method. The error bars indicate the standard errors of three biological replicates. Composition of the leaf extracts of the linalool-type, eucalypt-type and camphor-type are shown in Table 1; Composition of the leaf extracts of nerolidol-type and citral-type are shown in Table S9. and _LcTPS3_, a multifunctional enzyme that converts geranyl diphosphate to \(\alpha\)-thujene and (+)-sabinene [44]. In _Laurus nobilis_, the formation of 1,8-cineole, cadinenes and geranyllinalool catalyzed by TPS enzymes was characterized [28]. Sixty-seven unigenes were isolated from the transcriptome of _C. camphora_, which might be involved in terpene biosynthesis. The expression of _TPS14-like1_, _TPS14-like2_ and _TPS14-like3_ were upregulated in the bornecl phenotype relative to the linalool chemotype. These results are helpful to better understand the differential accumulation of terpen in different chemotypes of C. camphora [13]. This study analyzed the transcriptomes of three chemotypes of _C. poroctum_. In the eucalypt chemotype and linalool chemotype, the camphor chemotype and eucalypt chemotype, and the camphor chemotype and linalool chemotype comparison groups, 52, 49, and 66 candidate unigenes, respectively, were identified to be related to terpene biosynthesis. Furthermore, the terpenoid synthase genes _CpTPS1_, _CpTPS3_, _CpTPS4_, _CpTPS5_ and _CpTPS9_ had specific expression or higher expression in one of the chemotypes and may be involved in monoterpene biosynthesis. It is now generally accepted that MVA and MEP pathway activities are regulated at both the transcript and protein levels to control precursor availability [45]. Gene coexpression networks have revealed that there is no en bloc transcriptional regulation of all genes encoding MVA and MEP pathway enzymes.