Functional characterization of 2,3-oxidosqualene cyclase8 in Taraxacum mongolicum: overexpression enhances taraxasterol biosynthesis and antioxidant capacity

Taraxasterol, a pentacyclic triterpenoid compound, has been widely used in traditional and modern medicine because of its pharmacological properties such as anti-inflammatory, antioxidative and antitumor effects. 2,3-oxidosqualene cyclase (OSC) is highly important for the generation of phytosterols and triterpenoid compounds and the structural diversity of natural products. However, the specific role of TmOSCs in the taraxasterol biosynthesis pathway has not yet been precisely resolved. In this study, 10 TmOSC gene family members were identified via the Taraxacum mongolicum (dandelion) genome and classified into three subgroups. Phylogenetic and collinearity analyses revealed evolutionary conservation among OSC proteins from Asteraceae species. RNA-seq data analysis revealed that TmOSC8 and TmOSC10 were highly expressed in nutrient-containing tissues. In addition, methyl jasmonate (MeJA) and abscisic acid (ABA) significantly induced the expression of TmOSC3, and the change in its relative expression was consistent with the taraxasterol content. The relative expression level of the TmOSC8-overexpressioning line was significantly increased by approximately 20 fold compared with that of the wild type, and the content of taraxasterol was significantly increased to 3 fold greater than that of the wild type. This study systematically analyzed the evolutionary characteristics and expression patterns of the TmOSC gene family, suggested potential key roles of TmOSC3 and TmOSC8 in sterol synthesis and stress response, and provided a preliminary theoretical basis for the metabolic engineering of medicinal components in dandelion.