Analysis of the transcriptome and discovery of key enzyme genes of the triterpenoid saponin biosynthesis pathway in Akebia trifoliata (Thunb.) Koidz.

To understand the biosynthesis pathway and key enzymes of triterpenoid saponins in Akebia trifoliata (Thunb.) Koidz., transcriptome sequencing was performed on flowers, leaves, roots, and stems using the BGI Illumina HiSeq sequencing platform. After assembly, we obtained 57.25 Gb of data, including 140 859 unigenes with an average sequence length of 1350 bp. KEGG pathway enrichment analysis identified 517 unigenes involved in three metabolic pathways related to triterpenoid saponin biosynthesis, of which 415 unigenes encoded 19 key enzymes of the triterpenoid saponin biosynthesis pathway. Sequence analysis and homology modeling of squalene epoxide (SE), a key enzyme of triterpenoid saponin biosynthesis, revealed a conserved substrate-binding domain. Comparing gene expression levels in the stem, flower, leaf, and root of Akebia trifoliata showed that up-regulated genes were the richest between the stem and root, including 295 differentially expressed genes (DEGs) related to the triterpenoid saponin biosynthesis pathway.