## 3 Results
### Changes in Expression of Enzymes and Correlation with Content of Corresponding Metabolites  
To analyze the relationship between the gene expression of the terpene metabolic pathways and changes in aroma substance content, we determined the changes in terpene content at three stages of fruit development in three varieties, GLD608, GJ, and HDL, by using an untargeted metabolomics approach, and selected key volatiles for analysis, including \(\alpha\)-calacorene (C15H20), \(\alpha\)-cubebene (C15H24), _cis-\(\beta\)_-farnesene (C15H24), himachala-2,4-diene (C15H24), meridold (C15H26O), and linalool (C10H18O). Table 1 demonstrates the retention indices, retention times, and concentrations of the six major compounds for GLD608, GJ, and HDL at the three stages of green, transition, and red, where the concentrations provide the values for three replicate treatments. The results showed that there was no significant difference in the content of cis-\(\beta\)-farnesene during the green fruit stage of the variety, while the volatilization of other compounds took meaningful changes during the fruit development stage. Among them, the three developmental stages of HDL, the content of \(\alpha\)-calacorene (Figure 7A) and \(\alpha\)-cabebene (Figure 7B), is about 100 times higher than GLD608 during the green fruit stage, and about 300 times higher during the color transformation and maturity stages, indicating that HDL varieties have stronger woody aroma characteristics. _Cis-\(\beta\)_-farnesene (Figure 7C) and himachala-2,4-diene (Figure 7D) showed remarkable changes in their levels of expression at mid- to late fruit development in GJ and HDL. _Cis-\(\beta\)_-farnesene content in HDL was about 40-fold higher than that of GLD608 at the color-turning stage, and 60-fold higher at the mature stage. Himachala-2,4-diene volatilization was 600-fold higher in GJ than in GLD608 at the turn-color stage and about 500-fold higher at the mature stage, showing that GJ and HDL have the strongest pungent aroma at mid- to late fruit development. The higher volatility of linalool (Figure 7E) and meridold (Figure 7F) in GLD608 indicates that the variety possesses a stronger herbal aroma. Combined with analyses of distinct stages of expression in the same species, it was found that the content of \(\alpha\)-cubebene (Figure 7H) declined consistently in GLD608, whereas the content of _cis-\(\beta\)_-farnesene (Figure 7I) and himachala-2,4-diene (Figure 7J) increased notably in GJ. Of interest, the levels of key volatile substances were equivalent at different developmental stages of HDL, indicating stable synthesis as well as volatilization of the compounds. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Retention**} & \multirow{3}{*}{**Retention**} & \multirow{3}{*}{**Retention**} & \multirow{3}{*}{**Formula**} & \multicolumn{3}{c}{**Stage**} & \multicolumn{3}{c}{**Green Stage**} \\ \cline{3-14}  & & & & & \multicolumn{3}{c}{**Aroma Volatile**} & \multicolumn{3}{c}{**GLD608**} & \multicolumn{3}{c}{**GJ**} & \multicolumn{3}{c}{**HDL**} \\ \cline{3-14}  & & & & & & & & & & & & & & & & & \\ \hline
1540.6568602 & 29.957 & C15H2O & a-alcone & 0.290480591 & 0.3071  
Gene expression plays a vital role in the plant, which directly or indirectly affects the strength of metabolites. It is therefore reasonable to assume that these genes have a direct relationship with the formation of the corresponding compounds. _CaHMG5-3_ and _CaMVD-1_ are involved in the MVA metabolic pathway for the formation of sesquiterpene and diterpene compounds, while _CaCMK-1_ and _CaMECPS-1_ are involved in the MEP metabolic pathway for monoterpene compounds, and _CaGGPPS-2_ as well as _CaTPS-5_ are involved in the synthesis of downstream metabolites. By analyzing the correlation between the two genes, the correlation between the two genes is calculated as \(\rho_{1}\), \(\rho_{2}\), and \(\rho_{3}\). The correlation between the two genes is calculated as \(\rho_{1}\), \(\rho_{2}\), and \(\rho_{3}\).