[Transcriptome profiling of Saposhnikovia divaricata growing for different years and mining of key genes in active ingredient biosynthesis]

Saposhnikovia divaricata is a commonly used bulk medicinal plant. To explore the key enzyme genes and their expression in the biosynthesis of chromone and coumarin, the key active components, we carried out transcriptome sequencing(Illumina HiSeq) and bioinformatics analysis for the 1-year-old(S1) and 2-year-old(S2) plants of S. divaricata. A total of 40.8 Gb data was obtained. After the sequence assembly via Trinity, 110 732 transcripts and 86 233 unigenes were obtained, which were aligned and annotated with NR, Swiss-Prot, GO, KEGG, and PFAM. Daucus carota and S. divaricata had the highest sequence homology. KEGG pathway enrichment showed that the differentially expressed genes were mainly enriched in plant hormone signal transduction, phenylpropanoid biosynthesis, and flavonoid biosynthesis pathways. A total of 27 differentially expressed unigenes, including 13 enzyme genes, were identified in the pathways related to the synthesis of active ingredients in S. divaricata. Compared with S1 plant, S2 plant showed up-regulated expression of PAL, BGL, C4H, 4CL, CYP98A, CSE, REF, and CCoAOMT and down-regulated expression of CHS, CAD, and COMT. HCT and POD had both up-regulated and down-regulated unigenes. Among them, PAL, C4H, 4CL, BGL, and CHS can be used as candidate genes for the synthesis of the active ingredients in S. divaricata. The four key enzyme genes were verified by RT-qPCR, which showed the results consistent with transcriptome sequencing. This study enriches the genetic information of S. divaricata and provides support for the identification of candidate genes in the biosynthesis of secondary metabolites.