## 1 Introduction  
Terpenoids, phenylpropanoids/benzenoids, and fatty acid derivatives originate from divergent biosynthetic routes, and they largely constitute the floral scent of ornamental plants [1]. As the leading class of floral volatile compounds, terpenoids are derived from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are two common and interchangeable precursors [2]. Studies have shown that the two precursors are synthesized by the plastidic 2-C-methyl-D-erythitol-4-phosphate (MEP) and the cytosolic mevalonate (MVA) pathways. In both routes, the IPP and DMAPP syntheses are catalyzed by prenyltransferase to prenyl diphosphate such as geranyl diphosphate (GPP, C\({}_{10}\)), nervyl diphosphate (NPP, C\({}_{10}\)), _trans_/_cis_-farnesyl diphosphate (FPP, C\({}_{15}\)), and geranylgeranyl diphosphate (GGPP C\({}_{20}\)), among others [3]. The molecules are transformed into different terpene classes by variable-sized terpene synthases (TPSs) [4, 5]. For example, the TPSs catalytically convert GPP, FPP, and GGPP into monoterpenes (C\({}_{10}\)), sesquiterpenpens (C\({}_{15}\)) and diuterpens (C\({}_{20}\)), respectively. terpenoids are the most leading set of structurally and functionally diverse blends occurring in nearly all lifeforms [6, 7]. They are involved in plant fitness [8], multi-trophic interactions [9], and industrial applications [10]. Among terpenoids, rhodinol, largely made of geraniol and citronello, is widely known as \"liquidgold\". Traditionally extracted from roses, this \"liquid gold\" maintains a substantial market share and remains in high demand. Benzenoids/phenylpropanoids are the second most abundant family of plant volatile compounds [11]. Benzenoids/phenylpropanoids are exclusively derived from the aromatic amino acid phenylalanine (L-Phe), which is synthesized via either shikimate or arogenate plastitial pathways [12], a seven- and a three-multistep enzymatic process [1]. Phenylalanine ammonalyase (PAL) catalyzes L-Phe into cinnamic acid and represents the first committed step in benzenoid (C\({}_{6}\)-C\({}_{1}\)) and phenylpropene (C\({}_{6}\)-C\({}_{3}\)) biosynthesis [13]. In contrast to benzenoids and phenylpropenes, different routes for the biosynthesis of volatile phenylpropanol-related (C\({}_{6}\)-C\({}_{2}\)) compounds, such as phenylacetaldehyde (PAId) and 2-phenylethanol (2-PE), exist. In plants, 2-PE is synthesized in two major steps: the conversion of L-Phe into PAId followed by the subsequent conversion of PAId into 2-PE. There are at least four routes responsible for PAId biosynthesis in plants. As a recap, pyridoxal-5'-phosphate-dependent aromatic amino acid decarboxylase (AADC) or phenylacetaldehyde synthase (PAAS) converts L-Phe to PAId in roses and petunias [14]. Interestingly, an alternative pathway involving enzymes named aromatic amino acid aminotransferase (AAAT), which converts L-Phe into phenylpyruvate (PPA), and phenylpyruvate acidodecarboxylate (PPDC), converting PPA into PAId, has also been characterized in roses [15]. But this pathway seems to be season-specific and induced by high temperature in summer [16]. In tomato (_Solanum lycopersicum_), AADC has also been reported to convert L-Phe into 2-phenylethylamine which can be further catalyzed into PAId by an amino oxidase [17]. Recently, a cytochrome P450 family 79D protein CYP79D73 has been identified to catalyze the formation of \((E/Z)\)-phenylacetaldehyde (PAOx), an intermediate in the biosynthesis of 2-PE in Plumeria (_Plumeria rubra_) [18]. While a handful of genes and pathways have been pinpointed for the initial step from L-Phe to PAId, the conversion of PAId to 2-PE in plants is currently attributed solely to the short-chain reductase (SDR) phenylacetaldehyde reductase (PAR) [19]. In addition, fatty acid derivatives derived from the degradation of long carbon chains of lipids are mainly responsible for the herbaceous notes in the fragrance of flowers. For example, Z-3-hexenol confers certain rose varieties the characteristic smell of freshly cut grass [20].