## 1 Introduction
Plant terpenoids are a class of natural products characterized by the presence of two or more isoprene units on their fundamental carbon scaffolds. They can be categorized into various subclasses, such as monoterpenes, sesquiterpenes, diterpenes, and triterpenes, based on the number of isoprene units they contain [31]. The synthesis of terpenoids can be classified into two major pathways: the mexolonate (MVA) pathway and the 2C-methyl-d-erythriot-4-phosphate (MEP) pathway. The former is capable of producing sesquiterpenes and triterpenes in the cytoplasm of almost all eukaryotes and archaea, while the latter is restricted to synthesizing monoterpenes, diterpenes, and triterpenes in plastids found in eubacteria, algae, higher plants, and protists [32; 33; 34; 35; 36; 37]. In the MVA pathway, acetylCoA is catalyzed by a series of enzymes to form the precursor isopentenyl diphosphate (IPP), with 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) acting as the rate-limiting enzyme in this pathway [38]. In the MEP pathway, the glycolytic products glyceraldehyde-3-phosphate and pyruvate undergo several enzymatic reactions to produce dimethyl allyl diphosphate (DMAPP). The rate-limiting enzymes in this pathway are 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and 1-deoxy-D-xylulose-5-phosphate reducing isomerase (DXR) [39]. Reversible conversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) can be achieved through the action of isopentenyl diphosphate isomerase (IDI) [31]. These two substrates are catalyzed by farnesyl diphosphate synthase (FPS) to produce farnesyl diphosphate (FPP) [40], and by geranylgeranyl pyrophosphate synthase (GPPS) to produce geranyl pyrophosphate (GPP) and geranylgeranyl pyrophosphate (GGPP) [41]. Among them, FPP serves as the direct precursor for the biosynthesis of sesquiterpenes and triterpenes [42], GPP acts as the direct precursor for monoterpense synthesis, and GGPP functions as the direct precursor for the biosynthesis of diterpenes, carotenoids, and gibberellins [43]. Ultimately, these precursors undergo transformation into various types of sesquiterpenes, mediated by terpene synthases [44]. The majority of sesquiterpene compounds found in agarwood undergo catalysis by sesquiterpene cyclases to generate FPP. Consequently, the genes responsible for encoding sesquiterpene cyclases, particularly guaicacene synthase (GSs), which is widely distributed in agarwood, and their associated reaction mechanisms have garnered significant attention. The treatment of _A. crassua_ with methyl jasmonate (MJ) was found by [PERSON] and [PERSON] [45] to promote the expression of the \(\delta\)-guaiae synthase gene, leading to the induction of \(\alpha\)-guaiene, \(\alpha\)-humulene, and \(\delta\)-guaiene production. Additionally, a series of studies [4; 46; 47; 48; 49; 44; 34] have demonstrated that physical or chemical trauma, such as mechanical injury, exposure to marijuana (MJ), or treatment with formic acid (FA), can induce the expression of FPS-relatedgenes. This suggests a clear association between tissue injury and sesquiterpenothesis at the level of gene expression. Plant metabolomics is a crucial analytical tool that has been extensively utilized to assess the dynamic alterations of metabolites across various tissues, species, and developmental stages [50]. RNA-seq-based molecular bioprospecting approaches enable the identification of regulatory genes and account for variations in the expression levels of biosynthetic genes in relation to metabolite content [51]. A combined analysis of transcriptome data and metabolic profiles facilitates the identification of functional genes and the elucidation of primary and secondary metabolic pathways in plants [52; 53]. The integration of transcriptomics and metabolomics studies enables the exploration of the correlation between metabolites and genes, thereby elucidating the molecular regulatory mechanisms underlying metabolite dynamics [54; 55].