Identification and functional study of oleoresin terpenoid biosynthesis-related genes in masson pine (Pinus massonianaL.) based on transcriptome analysis

Masson pine (Pinus massonianaL.) is one of the most important species for oleoresin production worldwide. However, the mechanism of oleoresin synthesis in masson pine remains poorly studied. We revealed the key differentially expressed genes associated with terpenoid biosynthesis in trees with different yields of oleoresin in different tissues (trunk xylem and needle) during different seasons (spring and autumn) based on the combined application of the SMRT full-length transcriptome and Illumina RNA sequencing under field operations. A total of 76,754 full-length non-redundant transcripts were obtained in the study. Transcriptome data were annotated with KEGG and GO, and they have been shown to be of high quality by qRT-PCR. Chloroplastic 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway and cytosolic mevalonate (MVA) pathway genes have different preferences under different conditions. Moreover, the phylogenetic analysis results revealed three classes of DXS genes with different functions. Among the tissue-specific genes, AACT1 was expressed in the trunk xylem at the highest levels, while MCS (1, 4) and HDR2 were significantly upregulated in the needle. Among stage-specific genes, DXS6 and HDS6 were expressed in the trunk xylem in August (autumn) at the highest levels. Furthermore, all of the terpene synthase (TPS) differentially expressed genes (DEGs) were clustered into the gymnosperm-specific TPS-d subfamily, including sesquiterpene synthase and diterpene synthase genes. According to the protein sequence alignment, diTPS1 and diTPS5 with three conserved active sites catalysed the synthesis of diterpene resin acids. In the low-yield oleoresin clone, diTPS (1, 5) and GGPPS (4, 6) were upregulated in the trunk xylem. The integration of the transcriptomic data indicated that the AACT, MCS, HDR, DXS, HDS, and TPS (with two conserved active sites) may play critical roles in the terpenoids biosynthesis of masson pine. The results of our study can be useful for developing an understanding of the coniferous genome and to significantly accelerate confer breeding.