Integrated Analysis of the Transcriptome and Metabolome Reveals Genes Involved in the Synthesis of Terpenoids in Rhododendron fortunei Lindl.

Rhododendron, a globally popular ornamental flower, is nevertheless limited in our understanding of the mechanisms underlying its fragrance formation. Notably, terpenoids are the most prevalent volatile metabolite produced by plants. In this study, gas chromatography–mass spectrometry (GC–MS), liquid chromatography–mass spectrometry (LC–MS) and transcriptomics sequencing were conducted to analyze the synthesis mechanisms of terpenoid fragrance compounds of petals in fragrant R. fortunei Lindl. (YJ) and non-fragrant R. “Nova Zembla” (NW). The results identified that (-)-myrtenol, linalool, pinene, myrtenyl acetate, and terpineol were key floral aroma substances in YJ. Furthermore, an analysis of KEGG enrichment and differentially expressed genes (DEGs) revealed that the bud and decay stages exhibited the highest number of enriched DEGs among different aroma types, indicating these as critical stages for the synthesis of terpenoid floral compounds. In this study, a structural gene, denoted as RfFDPS, was identified as a negative regulatory gene for monoterpene accumulation and a positive regulatory gene for sesquiterpene accumulation in YJ. Utilizing subcellular localization technology, we determined that RfFDPS proteins are located in the cytoplasm. A functional analysis through transient expression and gene silencing of RfFDPS demonstrated its ability to regulate the accumulation of monoterpenes and sesquiterpenes. The overexpression of RfFDPS led to an increase in the expression of structural genes related to terpenoid synthesis, resulting in a decrease in monoterpenes and an increase in sesquiterpenes. Conversely, gene silencing had the opposite effect. In conclusion, RfFDPS plays a pivotal role in the synthesis and release of terpenoid volatile compounds in YJ petals, laying a solid theoretical foundation for the cultivation and enhancement of aromatic R. species.