| Summary: | Slash pine (<i>Pinus elliottii</i> Engelmann) 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 α- and β-pinenes 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 α- and β-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 <i>c215396.graph_c0</i> 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 <i>c215396.graph_c0</i> can activate the transcription of <i>Apetala 2</i> (<i>AP2</i>) and <i>1-deoxy<span style="font-variant: small-caps;">-</span></i><i><span style="font-variant: small-caps;">d</span></i><i>-xylulose 5-phosphate synthase</i> (<i>dxs</i>), 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.
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