## 4 Materials and Methods
### GC-MS Analysis  
VOCs were analyzed by an Agilent 7890A GC, coupled with a 5975C inert mass selective detector (Agilent Technologies, Santa Clara, CA, USA). An autosampler was used to inject the samples in splitless mode into a port heated to 250 \({}^{\circ}\)C and an oven heated to 50 \({}^{\circ}\)C. Separation was achieved using an HP-5 MS column (30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m) with helium carrier gas at a constant flow rate of 1 mL/min. The GC oven temperature was programmed from 50 \({}^{\circ}\)C (held for 1 min) to 300 \({}^{\circ}\)C at 8 \({}^{\circ}\)C/min and finally held at 300 \({}^{\circ}\)C for 5 min. MS measurements were performed in the scan mode with the scan range of m/z 50 to 350. C\({}_{7}\)-C\({}_{30}\) saturated alkanes were used for the calculation of retention indices. The MSD ChemStation data analysis program (Agilent Technologies, Santa Clara, CA, USA) was used for data processing. For VOCs analysis, peaks were identified by comparison of retention times, retention indices, and mass spectra with those from the National Institute of Standards and Technology (NIST) MS 2014 library. Peak areas of individual products were calculated as follows. Product (%) = (peak area of the product/sum of peak areas of all the products produced by a tissue) \(\times\) 100.  
For in vitro and in vivo analysis, peaks were identified by the comparison of retention times, retention indices, and mass spectra with entries in the NIST MS 2014 library and/or authentic standards. Authentic standards of \(\alpha\)-terpineol, \(\beta\)-caryophyllene, \(\alpha\)-caryophyllene, \(\beta\)-farnesene, and \(\alpha\)-longipinene were purchased (Sigma-Aldrich, St. Louis, MO, USA). Essential oils of _Cedrus atlantica_, _Helichrysum italicum_, and _Zingiber officinal_ were procured (Organic Infusions Inc., Camarillo, CA, USA). The suppliers of the essential oils provided the list of all volatile compounds with their retention times and quantities.  
Supplementary materials can be found at [[http://www.mdpi.com/1422-0067/21/22/8566/s1](http://www.mdpi.com/1422-0067/21/22/8566/s1)]([http://www.mdpi.com/1422-0067/21/22/8566/s1](http://www.mdpi.com/1422-0067/21/22/8566/s1)). Figure S1: Variation in quality and quantity among VOCs identified from Stevia tissues--leaves, flowers, stems, and roots, Figure S2: Molecular phylogenetic analysis of SrTPSs, Figure S3: Amino acid sequence alignment of SrTPSs, Figure S4: The mass spectra of terpenoids described in Figures 4 and 5, Figure S5: In vitro enzyme assay using heat-inactivated recombinant proteins, Figure S6: Expression analysis of homologs of Arabidopsis stress-induced marker genes in Stevia leaves and roots, Table S1: List of primers used in this study, Table S2: Abbreviations and accession numbers of proteins used in the phylogenetic analysis.  
**Author Contributions:** Conceptualization, I.-C.J.; methodology, S.D., M.J.K., H.J.C., and I.-C.J.; validation, S.D., M.J.K., H.J.C., and I.-C.J.; formal Analysis, S.D., M.J.K., and H.J.C.; resources, M.J.K., H.J.C., and S.H.L.; data curation, S.D., M.J.K., H.J.C., and I.-C.J.; Writing--Original Draft Preparation, S.D. and I.-C.J.; Writing--Review and Editing, S.D. and I.-C.J.; Supervision, I.-C.J.; Funding Acquisition, I.-C.J. All authors have read and approved the final manuscript.  
**Funding:** This work was supported by the Temasek Life Sciences Laboratory and, in part, by the National Research Foundation, Prime Minister's Office, Singapore, under its Synthetic Biology Research and Development Programme (Award No: SBP-P3).  
**Acknowledgments:** We thank the Temasek Life Sciences Laboratory central facility for support on confocal microscopy.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Accession Numbers:** The sequences of _SrTPS1-SrTPS5_ were submitted to the GenBank ([[https://www.ncbi.nlm.nih.gov](https://www.ncbi.nlm.nih.gov)]([https://www.ncbi.nlm.nih.gov](https://www.ncbi.nlm.nih.gov))) under accession numbers MW187850-MW187854.