Metabolic Stimulation-Elicited Transcriptional Responses and Biosynthesis ofAcylated Triterpenoids in the Medicinal Plant Helicteres Angustifolia

Abstract

Helicteres angustifolia has long been used in Chinese traditional medicine. It has multiple pharmacological benefits, including anti-inflammatory, anti-viral and anti-tumor effects. Its main active chemicals include betulinic acid, oleanolic acid, helicteric acid, helicterilic acid, and other triterpenoid sapions. It is worth noting that the acylation of triterpenoids, such as helicteric acid and helicterilic acid, are characteristic components of Helicteres and are relatively rare among other plants. However, reliance on natural plants as the only sources of these restricts the potential use of H. angustifolia. Therefore, engineering of its metabolic pathway is of high research value for enhancing the production of secondary metabolites. Unfortunately, little is known of the biosynthesis of acylated triterpenoids, hindering its further investigation. Here, the RNAs of different groups treated by metabolic stimulation were sequenced with an Illumina high-throughput sequencing platform, resulting in 121 gigabases of data. A total of 424,824 unigenes were obtained after the trimming and assembly of the raw data, and 22,430 unigenes were determined to be differentially expressed. In addition, three oxidized squalene cyclases (OSCs) and four Cytochrome P450 (CYP450s) were screened, of which one OSC (HaOSC1) and one CYP450 (HaCYPi3) achieved functional verification, suggesting that they could catalyze the production of lupeol and oleanolic acid, respectively. At the same time, we also screened two triterpenoid acetyl transferases (TATs) and one triterpenoid benzoyl transferase (TBT), as subsequent structural modificatory genes, their preliminary study laid a foundation for the acylation of triterpenoids. In a nutshell, these results shed light on the regulation of acylated triterpenoids biosynthesis.