De novo transcriptomic analysis and establishment of cell suspension culture system to improve saponin production in Oplopanax elatus

Oplopanax elatus, commonly called Asian devil’s club, is a valuable medicinal plant in the family Araliaceae that recommends itself as source of herbal preparations. Although triterpenoid saponins make up the major bioactive component of O. elatus, nothing is known about the genes that are involved in the biosynthesis of these complex compounds. To analyze the triterpenoid saponin biosynthetic pathway in O. elatus, we firstly generated a transcriptome library using Illumina HiSeq^TM2500 sequencing platform, and identified 122 unigenes encoding 47 putative enzymes in pathways for terpenoid backbone (MEP and MVA pathways) and triterpenoid saponin biosynthesis. The tissue-specific expression of selected genes suggests that the leaves of O. elatus are the main site of triterpenoid saponin biosynthesis. In addition, we established cell suspension culture of O. elatus to develop a sustainable source of naturaceuticals. The total saponin production in the cell suspension of O. elatus was significantly increased by melatonin at 195% at a dose of 100 µM compared with the mock-treated control. The expression analysis suggests that the enhanced production of saponins in melatonin-treated O. elatus is mediated by the increased transcription of genes involved in triterpenoid saponin biosynthesis pathway. Taken together, the transcriptome dataset generated in this study will serve as a valuable resource for accelerating genomic and functional genomic research in O. elatus, and our results provide valuable information for improving the production yield of saponins in plant suspension cultures.