## 1 Introduction  
Volatile terpen constitute the largest class of plant volatile compounds [1]. All plant organs, such as leaves, branches, flowers, and roots, can emit terpene volatiles to ensure healthy plant growth [2]. Petals are the main release parts of floral fragrance in many plants, such as rose (_Rosa_ spp.) [3]. The role of volatile terpenoids released from flowers is to attract pollinators, and to defense against biotic and abiotic stresses [4]. For example, geraniol has certain antibiotic activity and can be detected with high response by the honeybees' antennae [5]. The \(\beta\)-ccineme and linalool were common attracting compounds for pollinators and has antibacterial effect [6,7]. (_E_)-\(\alpha\)-farnesene released from the flowers of _Brassic rapq_ showed attraction of bees instead of butterflies [8], and (_E_)-\(\beta\)-caryophyllene is beneficial for plant fitness and functions in defense against pathogenic bacteria [9]. In most plants, the volatile terpenoids are constructed from two C\({}_{5}\) precursors, namely isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP), which are produced through either the methylerithritol phosphate pathway (MEP) in the chloroplast or the mevalonate pathway (MVA) in the cytosol [4,10]. Then, the IPP and DMAPP units are condensed by prenyltransferases (PTs, also referred to as isoprenyl diphosphate synthases or premyl diphosphate synthases) to form direct terpene precursors, such as geranyl diphosphate (C\({}_{10}\), GPP), famesyl diphosphate (C\({}_{15}\), FPP), or geranylgeranyl diphosphate (C\({}_{20}\), GGPP) [11]. Subsequently, terpene synthase (TPS), which is the primary enzyme in the terpenoid biosynthetic pathways, converts the precursors into various terpene products, such as monoterene (C\({}_{10}\)), sesquiterpene (C\({}_{15}\)), and diterpene (C\({}_{20}\)) [12]. These products can undergo further modifications under the action of various enzymes, such as dehydrogenases, methyltransferases, acyltransferases, and glycosyltransferases to form highly diverse metabolites [13; 14]. Rose is widely cultivated as a garden plant for the cut-flower industry, and floral fragrance is a vital characteristic of ornamental roses [14; 15]. The terpenoid volatiles in the floral rose scent are mainly monoterenes and sesquiterpenes, as well as their derivatives. Compared with moderately and less fragrant rose cultivars, the very fragrant cultivars produced a certain amount of monoterponoids, including geraniol, citronellol, and nerol, all three of which have roeselike fragrances [16]. In addition, the aldehyde and acetate ester derivatives of these three compounds were also produced [16; 17]. Other monoterponoids including \(\alpha\)-pinene, \(\beta\)-pinene, limonene, and linalool are emitted at low levels in rose floral scent [17]. Sesquiterpenes, including germacrene D, \(\delta\)-cadinene, \(\alpha\)-copaene, \(\alpha\)-cubenene, \(\beta\)-cubenene, \(\beta\)-elemene, and \(\beta\)-caryophyllene, are emitted from rose flowers, whereas germacrene D was highly released from some rose cultivars [17; 18; 19; 20]. Only several genes involved in the biosynthesis of rose volatile terpen have been identified. The first TPS gene cloned in rose was germacrene D synthase (_RhGDS_), which catalyzes the substrate FPP to germacrene D as a unique product [20]. Three TPS genes, namely _RcLINS_, _RcLIN-NERS1_, and _RcLIN-NERS2_, have been characterized, and the expression levels of these genes were low in rose petals [21]. _RcLINS_ belonging to the TPS-b subfamily is responsible for the presence of a small amount of (_3R_)-(-)linalool in rose scent. The bifunctional _RcLIN-NERS1_ and _RcLIN-NERS2_, belonging to the TPS-g subfamily, produce (_3S_)-(+)-linalool and nerolidol when incubated with GPP and FPP, respectively, whereas _RcLIN-NERS3_ has been identified as a pseudogene. Moreover, a novel TPS-independent pathway for monoterpene biosynthesis was described in rose [22].