## 1 Introduction
These intermediates serve as direct precursors for terpene synthase (TPS), which then synthesizes various complex and diverse terpene compounds with a large number of structures [27; 28]. Terpenes, as the primary constituents of aromatic compounds, have garnered substantial attention in ornamental plants, such as roses and freesias. Studies have shown that monoterenes account for up to 70% of the aroma in some roses [29], and terpene synthase exhibits specific expression patterns in freesia flowers [30]. In a study by [PERSON], et al. [31], it was found that geraniol, which is a fundamental characteristic of rose aroma, is synthesized through the MVA pathway from the bifunctional RCG/FPPS1, producing both GPP and FPP. The study elucidates the origin of the cytosolic GPP for geraniol production and suggests that _RCG/FPPS1_ plays a key role in the biosynthesis of volatile terpenoids in roses. Therefore, different structural genes may play different roles in different species. In recent years, high-throughput omics techniques, including genomics, transcriptomics, proteomics, and metabolomics [32], have advanced rapidly. The combined analysis of metabolomics and transcriptomics has been widely used to study the relationship between secondary metabolite content in plant organs and the corresponding differentially expressed genes (DEGs) [33]. For instance, researchers have employed metabolomics and transcriptomics to dissect the antifreeze mechanism in naturally overwintering tea trees under freezing stress, analyzing their antifreeze mechanism. Meanwhile, [PERSON] et al. [34]conducted metabolomics and transcriptomics analyses to elucidate floral aroma composition and biosynthesis in male sterile chematis varieties. [PERSON] et al. [35] used GC-MS and transcriptomics to determine the complete outline of terpenoid biosynthesis pathways in hoya. Similarly, [PERSON], et al. [36] utilized high-throughput transcriptomics and metabolomics to examine the variation in metabolite composition and related gene expression in _Ginkgo biloba_ leaves across different developmental stages and tree ages, thereby facilitating the identification and analysis of key genes involved in terpenen biosynthesis. Therefore, multi-omics joint analysis is an effective approach to exploring the mechanism of rhododend fragrance synthesis. The study aimed to gain deeper insights into the mechanisms that govern the formation of rhododendron fragrance during growth and development. It utilized transcriptome and metabolomics analyses on the petals of fragrant _R. fortunei_ Lindl. and non-fragrant _R._ \"Nova Zembla\" at varying stages. The use of RNA-seq technology can help screen and identify candidate genes involved in the formation of rhododendron fragrance and analyze gene expression patterns. By applying non-targeted metabolomics detection technology, various VOCs synthesized and accumulated in the pathway are comprehensively detected, screening for key floral aroma compounds based on differential expression of metabolites in _R. fortunei_ Lindl. Through multi-omics joint analysis, we explore the interplay between related genes, metabolites, metabolic pathways, and the production of rhododendron fragrance. This study provides novel insights into the molecular mechanism of the aromatic compound synthesis in rhododendron, thus serving as a scientific foundation for breeding new fragrant rhododendron varieties.