###### Abstract  
Slabn pine (_Pinus ellitotti_ [PERSON]) is a pine species widely cultivated for its high oleoresin production capacity. However, little is known about the underlying molecular mechanism of oleoresin biosynthesis between high and low oleoresin-yielding slash pines. In this study, the terpenoid compositions of oleoresin harvested from high- and low-yielding slash pines were identified using gas chromatography/mass spectrometry (GC-MS) analysis. The monoterpenes and diterpenes are the major constituents, of which the \(\alpha\)- and \(\beta\)-pinnes are the overwhelming majority of turpentines, and abietic acid, levopimaric acid, and neoabietic acid are the most abundant in rosin. The transcriptomic analysis was also performed with secondary xylem tissues of high- and low-yielding slash pines. After functional annotation, the DEGs of RNA-seq data between high- and low-yielding pines in April, July, and October were screened, and many key enzyme genes were found to be implicated in terpenoid backbone biosynthesis. Moreover, weighted gene correlation network analysis (WGCNA) was carried out to uncover the gene modules highly related to \(\alpha\)- and \(\beta\)-pinene biosynthesis in slash pine. Twenty-three modules were attained in this study. Focusing on the total oleoresin yield, the MEblue module exhibited the highest positive correlation, while the MEgreen module exhibited the highest negative correlation. A total of 20 TFs were identified in gene modules. Among these genes, the _c215396_graph_c0_ encoding an MYB TF is the key differentially expressed gene (DEG) between high- and low-yielding pines. The subsequent one-hybrid yeast assay verified that _c215396_graph_c0_ can activate the transcription of _Apetala 2 (AP2)_ and _1-deoxy-D-xylulose 5-phosphate synthase (dxs)_, which are also two DEGs between high- and low-yielding pines. Thus, our study identified a set of key enzymes and TFs that are involved in regulating oleoresin and composition between high- and low-yielding slash pines and provided us a deep insight into oleoresin biosynthesis. Pinus ellitotti Engelmann; comparative transcriptomic analysis; resin yield; oleoresin biosynthesis; WGCNA 2022202202202202202202202202022020202020202020220202020202020202202020202020202020220202020202020202020202022020202020202020202020202020202022020202020202202022020202020220202202202022  
As the foremost source of terpenoids, natural vegetation provides over 30,000 terpenes with enormous structural diversities and complexities [1; 7; 8]. The biosynthesis of terpenes initiates with the formation of two substrates, the simple C\({}_{5}\)-unit isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). Two separate metabolic pathways, the mevalonate (MVA) and methyl-erythnitol 4-phosphate (MEP) pathways, are responsible for the formation of C\({}_{5}\)-unit IPP and DMAPP in cytosol and plastids, respectively [9]. The synthesized DMAPP and IPP are the building blocks that undergo further condensation reactions to form the direct precursors of terpenes, including the C\({}_{10}\)-unit liner prenyl diphosphpates geranyl diphosphate (GPP), C15-unit farnesyl diphosphate (FPP), and C\({}_{20}\)-unit geranylgeranyl diphosphate (GGPP) [10]. These condensation reactions are catalyzed by the short-chain isoprenyl diphosphate synthases (IDSs) that belong to a large enzyme class, also known as pretytransferases [11; 12]. In the MEP pathway, geranyl diphosphate synthase (GPP synthase) condenses one molecular DMAPP with two IPP molecules to produce GPP, while the formation of GGPP needs one molecular DMAPP and three IPP molecules under the catalyzation of geranylgeranyl diphosphate synthase (GGPP synthase) in plastids [10; 13; 14]. In contrast, the biosynthesis of FPP from DMAPP and one molecular of IPP is primarily mediated by farnesyl pyrophosphate synthases (FPP synthase) that function downstream of the MVA pathway occurring in cytosol [10; 14].