## 3 Results
### Joint Analysis of Transcriptome and Metabolome  
To elucidate the relationship between related genes and metabolites during flowering, we conducted an analysis of terpene metabolites and nine selected genes involved in  
Figure 8: Relative expression changes in candidate genes in rhododendon varieties (YJ and NW) across different developmental stages (A, B, C, D).  
the terpene synthesis pathway. The large number of metabolites detected using GC-MS is consistent with the trend of differential gene regulation. Among them, pinene, bicyclo[3.1.0]hexane, 4-methylene-1-(1-methylethyl)-, 2,3-dehydro-1,8-cineole, trans-linal oxide (furanoid), cis-muurola-4(15), 5-diene, myrtenyl acetate, terpineol, and (-)-myrtenol exhibited consistent expression patterns with those of _TPS_, _FDPS_, _GGPS_, _HMGR_, and _AACT_.  
Among the groups, in YJ1 vs. NW1, trans-linalool oxide (furanoid) and cis-muurola-4 (15), 5-diene exhibited positive correlations with _TPS_, _FDPS_, and _AACT_ (Figure 9A). In YJ2 vs. NW2, cis-muurola-4(15),5-diene showed a significant positive correlation with _TPS_ and _FDPS_, while myrtenyl acetate was positively correlated with _GGPS_ (Figure 9B). In YJ3 vs. NW3, (1R)-2,6,6-trimethylbicyclo[3.1.1]hept-2-ene was significantly positively correlated with _TPS_ and _AACT_, while bicyclo[3.1.0]hexane, 4-methylene-1-(1-methylethyl)- was significantly positively correlated with _HMGR_ and negatively correlated with _HMGS_. In contrast, linalool is negatively correlated with a multitude of genes. Additionally, there was a significant positive correlation between myrtenyl acetate and _GGPS_ (Figure 9C). Finally, in YJ4 vs. NW4, a significant positive correlation was observed between numerous metabolites and _HMGS_ (Figure 9D).  
Among these, in the comparison between YJ2 and YJ1, the Unigene528_All in the _AACT_ enzyme gene specifically demonstrated a positive correlation with a substantial number of volatile terpen (Supplementary Figure S10A). In the YJ3 vs. YJ2, bicyclo[3.1.0]hexane, 4-methylene-1-(1-methylethyl)- was negatively correlated with _TPS_ specificity, whereas myrtenyl acetate was negatively correlated with _FDPS_ specificity (Supplementary Figure S10B). Lastly, in YJ4 vs. YJ3, all compounds except for 2,3-dehydro-1,8-cineole were positively correlated with _TPS_ and _HMGR_ and negatively correlated with _HMGS_ specificity (Supplementary Figure S10C).  
Through the joint analysis of the main volatile terpenoid metabolites and candidate genes, we identified significant positive correlations between key substances such as myrtenyl acetate, pinene, (-)-myrtenol, and terpineol, and _FDPS_ during the flowering stage. A KEGG enrichment analysis revealed that ko00909 is the pivotal metabolic pathway that significantly influences the expression of different aroma types in rhododendrons. Ultimately, we determined that _FDPS_, the key enzyme gene for ko0090, is the key gene for regulating YJ volatile terpenoid aromatic compounds. The content of precursor non-volatile metabolites formed by similar metabolites also exhibited significant correlations, indicating their involvement in regulating YJ aroma. However, further experimental verification is required to elucidate how these key genes participate in the regulation of YJ aroma. In this study, the function of _RfFDPS_ was validated through transient overexpression and gene silencing experiments.