Identification of genes associated with the biosynthesis of protostane triterpenes based on the transcriptome analysis of Alisma orientale (Sam.) Juz

Protostane triterpenes in Alisma orientale (Sam.) Juz., because of their unique structural feature, exhibit distinctive pharmacological activities. However, the biosynthetic pathways for these compounds remain largely unknown. In this study, transcriptome analysis was performed using A. orientale tubers and leaves. We identified 101,107 unigenes, which were annotated against various databases. Importantly, 35 unigenes associated with the terpene biosynthesis pathway were identified, among which 18 encoded key enzymes catalyzing every reaction in the biosynthesis of protostane triterpenes skeleton. In addition, eight candidate transcription factor unigenes and nine candidate cytochrome P450 unigenes related to the terpene biosynthesis pathway were obtained. Moreover, the expression levels of most genes involved in protostane triterpenes biosynthesis in tubers were significantly higher than those in leaves. Furthermore, significant positive correlations were showed between the levels of key enzymes (HMGR2, SS2, SE1, SE2, OSC1, and OSC2), and the contents of the main bioactive compound at different developmental phases of A. orientale. These genes were identified first time in this study. These results provide preliminary evidence that these proteins may play crucially regulatory roles in protostane triterpenes synthesis.