**5. Conclusions**

In this study, we reported on the identification of 34 *DoTPS* genes in *D. o*ffi*cinale*. Their conserved motifs, exon–intron distribution, and phylogenetic analysis was assessed. Differential expression patterns of *DoTPS* genes exposed to ten different organs and three flowering stages, highlights their involvement in regulating the biosynthesis of floral monoterpenes, as well as the responses of plants to exogenous MeJA treatment, cold, and osmotic stress. One monoterpene synthase (DoTPS10), which was targeted to chloroplasts, could specifically convert GPP into linalool in vitro. Our findings show that transcript accumulation of multiple *TPS* genes is mainly responsible for the formation of floral terpenes, and provides a foundation for further studies on orchid floral scent research through the regulation of *DoTPS* genes.

**Supplementary Materials:** Supplementary materials can be found at http://www.mdpi.com/1422-0067/21/15/ 5419/s1.

**Author Contributions:** Conceptualization, Z.Y. and J.A.T.d.S.; methodology, Z.Y.; validation, Z.Y., C.Z., G.Z.; formal analysis, G.Z.; investigation, Z.Y.; resources, J.D.; data curation, Z.Y. and C.Z.; writing—original draft preparation, Z.Y., C.Z. and J.A.T.d.S.; writing—review and editing, J.A.T.d.S. and Z.Y.; visualization, Z.Y. and J.A.T.d.S.; supervision, J.D. and J.A.T.d.S.; project administration, J.D.; funding acquisition, J.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Key Research and Development Program of China, grant number 2018YFD1000400 and National Natural Science Foundation of China, grant number 31871547.

**Acknowledgments:** The authors are grateful to Yongxia Jia and Yangyang Xiao for assistance with GC-MS analysis of terpene compounds. We thank all the colleagues in our laboratory for help and advice. We would like to thank both the editor and reviewers for evaluating and providing constructive comments on this manuscript.

**Conflicts of Interest:** The authors declare no conflicts of interest.
