Transcriptome-based analysis of key functional genes in the triterpenoid saponin synthesis pathway of Platycodon grandiflorum.

Background: Platycodon grandiflorum (P. grandiflorum) is a commonly used medicinal plant in China. Transcriptome sequencing studies of different tissues of P. grandiflorum have been widely conducted. However, studies on transcriptome sequencing and expression patterns of key genes in the saponin synthesis pathway of Tongcheng P. grandiflorum, a high-quality medicinal resource of different years, are relatively limited.

Results: This study involved transcriptome sequencing and bioinformatics analysis of the roots from annual, biennial, and triennial P. grandiflorum in the Tongcheng area. After data filtering and assembly, we obtained 111.44 Gb of clean base data, including 742,880616 clean reads. We identified 5,156 differential expression unigenes between at least two sample groups, with differences noted among annual, biennial, and triennial P. grandiflorum plants. GO enrichment analysis annotated 3509, 1819, and 1393 DEGs in comparison TC1vsTC2, TC1vsTC3, and TC2vsTC3, respectively. Furthermore, KEGG enrichment analysis identified 16 genes encoding key enzymes in the terpene skeleton biosynthesis, sesquiterpene and triterpene biosynthesis pathways, including SE, AACT, FPPS, DXR, HMGR, HMGS, and DXS. The results of qRT-PCR experiments showed that most of the genes were most highly expressed in annual P. grandiflorum.

Conclusions: The present study provided transcriptomic data from the roots of Tongcheng P. grandiflorum of different years, which provides critical bioinformatics data on the growth and development of P. grandiflorum, laying a foundation for further research on saponins and identifying key enzymes involved in this process across different growth stages.