## 5 Conclusions  
Transcriptome sequencing was performed in the young leaves of _R. glutinosa_ Beijing No. 3, Huaifeng, and Jin No. 9 cultivars. Meanwhile, transcriptomes from the tuberous and adventitious roots of the Jin No. 9 cultivar were also constructed. Using the comparative transcriptome analysis, many important candidate genes that participated in catalpol biosynthesis were identified, such as CYP450, UGTs, oxidoreductase, hydroxylase, and decarboxylases. In addition, _RgGES1_ and _RgGES2_ were isolated and characterized as geraniol synthase, which catalyzed GPP to produce the precursor geraniol. The findings in this study will facilitate functional studies of catalpol biogenesis in _R. glutinosa_.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/genes15020155/s1](https://www.mdpi.com/article/10.3390/genes15020155/s1)]([https://www.mdpi.com/article/10.3390/genes15020155/s1](https://www.mdpi.com/article/10.3390/genes15020155/s1)), Supplementary Figure S1: The _R. glutinosa_ plant; Supplementary Figure S2: The flowchart to the Material and Method section for summarizing methodology; Supplementary Figure S3: The error rate distribution of unigenes; Supplementary Figure S4: The melting curves of the genes chosen for qRT-PCR analysis; Supplementary Figure S5: The heatmap of differentially expressed genes that were evaluated in this study; Supplementary Figure S6: Agarose gel electrophoresis for PCR products of _RgGES_;Supplementary Figure S7: The SDS-PAGE analysis of the recombinant RgGES1 and RgGES2 protein; Supplementary Table S1: Primers used in this study; Supplementary Table S2: Transcriptome assembly statistics for _R. glutinosa_; Supplementary Table S3: Annotation of unigenes in KOG database; Supplementary Table S4: KEGG classification of all the unigenes; Supplementary Table S5: Summary of annotated unigenes in GO database; Supplementary Table S6: Candidate unigenes of common enzymes in _route I_ and _route II_; Supplementary Table S7: Candidate UGT unigenes in _R. glutinosa_ transcriptomes; Supplementary Table S8: Accession numbers of PSPGs used for phylogenetic analysis in Figure 6; Supplementary Table S9: Aldehyde dehydrogenase unigenes identified in _R. glutinosa_ transcriptomes; Supplementary Table S10: NADP\" oxidoreductase candidate genes in _R. glutinosa_ transcriptomes; Supplementary Table S11: CYP450 unigenes identified in _R. glutinosa_ transcriptomes; Supplementary Table S12: Putative dehydratase genes in _R. glutinosa_ transcriptomes; Supplementary Table S13: Dexnboxylase candidate genes in _R. glutinosa_ transcriptomes; Supplementary Table S14: Putative hydroxylase and epoxidase genes involved in catalpol biosynthesis; Supplementary Table S15: Accession numbers of TPSs used for phylogenetic analysis in Figure 8.  
Conceptualization, Y.L., L.H., W.F. and X.Z. ([PERSON]); data curation, Y.L. and X.Z. ([PERSON]); formal analysis, Y.L.; funding acquisition, Y.L. and X.Z. ([PERSON]); investigation, Y.L., X.Z. ([PERSON]), L.M., L.Z. and N.A.; methodology, Y.L., L.H. and W.F.; validation, Y.L. and X.Z. ([PERSON]); writing--original draft, Y.L.; writing--review and editing, N.A., L.H., W.F. and X.Z. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 82204571.  
Not applicable.  
The transcriptome data have been deposited in the publicly accessible Genome Sequence Archive (GSA) database in the BIG Data Center under the accession number CRA005581. _RgGES1_ and _RgGES2_ were submitted to the GenBank database in the BIG Data Center under the accession number C_AA047852.1 and C_AA047853.1, respectively.  
We thank [PERSON], who is from the College of Pharmacy, Henan University of Chinese Medicine, for providing the _R. glutinosa_ material.  
The authors declare no conflicts of interest.