## 2 Results
### Spatiotemporal Expression Pattern of _Cp_GPPS/GGPPS Genes  
In plants, the formation of VOCs is a spatially and developmentally regulated phenomenon [4; 24; 25]. The transcript level of _Cp_GPPS/GGPPS genes was examined using real-time quantitative polymerase chain reaction (qRT-PCR) in various plant tissues, including the stamen, pistil, petal, flower, and leaf. Relative expression levels of all the _Cp_GPPS/GGPPS genes were compared with reference to the relative expression of _CpGGPPS2_ in the stamen. All the _Cp_GPPS/GGPPS genes showed variation in the spatial expression intensities. Among the five genes, _CpGPPS.SSU1_ and _CpGGPPS1_ showed the highest transcript, followed by _CpGPPS_, _CpGPPS.SSU1_, and _CpGGPPS2_. In detail, _CpGPPS.SSU1_ and _CpGGPPS1_ genes were highly expressed in the petal and flower but had low expression levels in the leaf, pistil, and stamen. Moreover, _CpGPPS.SSU1_, _CpGPPS_, and _CpGGPPS2_ were expressed in all the examined tissues, with high transcript levels in the petal (Figure 2).  
The temporal expression analysis of _Cp_GPPS/GGPPS genes in flowers revealed that all genes had the lowest expression levels in stage 1 (Figure 3). Moreover, the expression levels of all _Cp_GPPS/GGPPS genes, except _CpGGPPS2_ genes, increased gradually and reached a peak in stage 4, whereas their expression levels were significantly decreased in stage 5 (Figure 3). Interestingly, a prominent change in the temporal expression profile was observed for _CpGPPS.SSU1_ and _CpGGPPS1_ genes. Their level of expression was significantly increased in stage 4, which was approximately 245- and 35-time higher than that of stage 1, respectively (Figure 3).  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Gene/ cDNA Name**} & \multirow{2}{*}{\begin{tabular}{c} **ORF Length** \\ **(aa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Theoretical** \\ **pI Value** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Molecular** \\ **Weight (kDa)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **In Silico** \\ **Subcellular** \\ **Localization** \\ \end{tabular} } & \multirow{2}{*}{**Conserved Motif**} \\  & & & & & **Prediction** \\ \hline _CpGPPS.SSU1_/c81471 & 306 & 7.07 & 33.00 & Chloroplast & CxxxC, CxxxC \\ _CpGPPS.SSU2_/c64849 & 341 & 5.75 & 37.60 & Chloroplast & CxxxC, DDX(2\_4)D, CxxxC \\ _CpGPPS_/c90672 & 428 & 5.85 & 46.84 & Mitochondria & DDX(2\_4)D, DDxD \\ _CpGGPPS1_/c80517 & 377 & 6.47 & 40.85 & Chloroplast & CxxxC, DDX(2\_4)D, DDxD \\ _CpGGPPS2_/c51170 & 384 & 5.97 & 41.39 & Chloroplast & CxxxC, DDX(2\_4)D, DDxD \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of _Cp_GPPS/GGPPS genes.  
Figure 1: Phylogenetic and gene structure analysis of the wintersweet geranyl diphosphate synthase (GPPS)/geranylgeranyl diphosphate synthase (GGPPS). (**A**) The phylogenetic tree was generated by the neighbor-joining method using the MEGA 7.0, after alignment of deduced amino acid sequences by ClustalW. Numbers in the nodes are the bootstrap support values from 1000 replicates. The accession numbers are given in parenthesis. (**B**) Schematic genomic structure of _Cp_GPPS/GGPPS genes. The green box represents the exon and the black lines between them denote intron. The dark orange box represents the untranslated region.