## 5 Conclusions  
In the present study, the terpenoid compositions of oleoresin in high and low resin-yielding slash pines were explored, and monoterenes and diterpenes were identified to be the major components. The \(\alpha\)- and \(\beta\)-pinenes make up the majority of monoterenes and abietic acid, levopimaric acid, and neoabietic acid are most abundant in diterpenes. However, these terpenoids occupy different proportions in oleoresin produced by high- and low-yielding slash pine. Moreover, the RNA-seq analysis, depending on the secondary xylems of high- and low-yielding pines, provides a comprehensive transcriptional profile for future research. In RNA-seq data, a series of DEGs associated with terpenoid backbone biosynthesis were characterized, including _ispF/G/S_, _dxs_, _SPS_, _PT30_, _idsA_, _ZFPS_, _QH6_, etc., which are widely implicated in the MEP pathway and downstream terpenoid biosynthesis processes. Furthermore, the WGCNA analysis and subsequent one-hybrid yeast assay identified a MYB TF gene (_c215396_graph_c0_). _c215396_graph_c0_ is a key gene that functions as a transcriptional activator regulating the expression of _dxs_ and _AP2_ (Figure 6). These genes contribute to the differential \(\alpha\)-pinene content in high- and low-yielding pines. In summary, our work identified and characterized the crucial genes and gene modules involving in terpenoid biosynthesis that constitute a complicated gene regulation network differentially controlling the oleoresin yield and composition in high- and low-yielding slash pines.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/f13081337/s1](https://www.mdpi.com/article/10.3390/f13081337/s1)]([https://www.mdpi.com/article/10.3390/f13081337/s1](https://www.mdpi.com/article/10.3390/f13081337/s1)), Figure S1: Total yields of pine oleoresin from low- or high-yielding slash pines from April to October; Figure S2: Network heatmap plot of these 23 modules; Figure S3: GO enrichment analysis of genes of MEblue module in relation to the total content of pine oleoresin. Data S1: Sequences used for yeast one-hybrid assay; Table S1: Primers used for RT-PCR assay and yeast one-hybrid assay; Table S2: Terenoid compositions of oleoresin harvested from 16 selected high- and low-yielding slash pines in April, July, and October; Table S3: List of DEGs between P4 L vs. P4 H; Table S4: List of DEGs between P7 L vs. P7 H; Table S5: List of DEGs between P10 L vs. P10 H; Table S6: KEGG enrichment results of the DEGs between low- and high-yielding slash pines in April, July, and October; Table S7: Distribution of hub genes in each candidate modules; Table S8: Terenoid compositions of oleoresin harvested from 4 highest and 4 lowest oleoresin-yielding slash pines in April, July, and October.  
Conceptualization, M.Y. and M.L.; data curation, M.Y.; formal analysis, L.Z. and Y.G.; funding acquisition, M.Y. and M.L.; investigation, Z.C., R.H., Y.G. and S.Y.; methodology, M.Y., Z.C., R.H. and Y.G.; project administration, M.L.; resources, L.Z. and S.S.; software, C.J.; supervision, M.L.; validation, M.Y., Z.C., R.H. and Y.G.; writing-original draft, M.Y.; writing-review and editing, M.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by several programs, including the National Natural Science Foundation of China (No.32160385 and 31860220), the Jiangxi Province Science Foundation for Youths (No. 20212 BAB215013), the Science and Technology Research Project of Education Department of Jiangxi Province (No. GJJ200407), and the Science and Technology Leader Foundation of Jiangxi Province (No. 20212 BCJ23011).  
Not applicable.  
We thank the editor and reviewers for their constructive comments and advice on our manuscript.  
All authors declare no conflicts of interests.