## 1 Introduction  
The floral fragrance of plants serves multiple functions, including the attraction of pollinators, the provision of resistance to physical threats, and the defense against pests, herbivores, and pathogens [1]. Typically, floral fragrances consist of a range of low-molecular-weight secondary metabolic volatiles, with terpenes, aliphatic compounds, benzene ring/phenylpropane compounds, sulfur compounds, and nitrogen-containing compounds constituting the primary components [2]. Among these, terpenoids are particularly significant in the floral aroma of many plant species due to their structural diversity and widespread occurrence across various organisms. Notably, terpenoids play a crucial role in the floral fragrance of _Dendrobium_ species, including _D. loddigesii_, _D. chrysotoxum_, _D. _official_, and _D. hancockii_[3, 4, 5, 6, 7]. The synthesis of terpenoids involves two interconnected yet distinct pathways: the mevalonate (MVA) pathway in the cytoplasm and the 2-C-methyl-D-erythnitol-4-phosphate (MEP) pathway in the plastid [8; 9]. These pathways produce the structural units isopentenyl pyrophosphate (IPP) and dimethyl allyl pyrophosphate (DMAPP). The C5 precursors, DMAPP and IPP, subsequently lead to the formation of direct precursors like farnesyl diphosphate (FPP), geranyl diphosphate (GPP), and geranylgeranyl diphosphate (GGPP). In the cytosol, FPP is converted to sesquiterpene via the first pathway, in contrast, the second pathway that occurs in the plastid leads to the conversion of GPP to monoterenes and GGPP to dieterpenes [10]. At the branching point of the isoprenoid pathway, TPS plays a crucial role in influencing the diversity of plant terpenoids. The types and activities of TPS within the TPS family are essential for the synthesis of aromatic terpen in fragment-flowered plants. The type and expression of TPS genes are vital in the biosynthesis and accumulation of terpenoids, serving as significant regulators of plant floral fragrance [1; 4]. While several TPSs responsible for aromatic terpen synthesis have been identified in ornamental plants such as _Lilium_[11], _Jasminum_[12], _Cymbidium_[13], and _Phalanopsis_[14], only _Dendrobium officinal_ within the genus _Dendrobium_ has been extensively studied. [PERSON] et al. [15] identified an important candidate gene for the monoterpenoid synthase geraniol synthase (GES), _DoGES1_, and verified its function through prokaryotic expression and transgenic experiments in a model plant. Subsequently, [PERSON] et al. (2021) associated 13 _DoTPS_ genes with terpenoid floral aroma compounds through transcriptional and metabolic joint analysis of two different cultivated varieties of _Dendrobium officinal_. [PERSON] et al. concluded that DoTPS10 functions as a single-product enzyme (converting GPP to linalool), which can be upregulated by DobHLH4 [16; 17]. However, the functions and mechanisms of action of TPS in _Dendrobium Sw._ remain to be elucidated. The assembly and release of the chromosomal-level genome of _Dendrobium chrysotoxum_ have facilitated improved material selection for investigating the mechanism underlying aroma synthesis in this fragment species [18]. Through a combined analysis of transcriptional metabolism, we examined the composition and dynamic changes in the floral aroma in _Dendrobium chrysotoxum_, elucidating the critical role of aromatic terpenoids in the formation of its floral characteristics. As the density of terpen accumulates during the flowering period, the expression of certain genes is upregulated. Then, three TPSb genes (_DcTPSb1_, _DcTPSb3_, and _DcTPSb4_) that exhibited a strong correlation with terpene compounds at bloom were identified [4; 19]. Of the three, _DcTPSb1_ demonstrated the highest expression level in RNA-seq across the three flowering periods, showing a significant correlation with the accumulation of seven representative aromatic monoterpenes in the floral components of _Dendrobium chrysotoxum_.