Genome-Wide Identification and Characterization of OSC Gene Family in Gynostemma pentaphyllum (Cucurbitaceae)

<i>Gynostemma pentaphyllum</i> is a traditional Chinese medicinal plant of considerable application value and commercial potential, primarily due to its production of various bioactive compounds, particularly dammarane-type triterpenoid saponins that are structurally analogous to ginsenosides. Oxidosqualene cyclase (OSC), a pivotal enzyme in the biosynthesis of triterpenoid metabolites in plants, catalyzes the conversion of oxidosqualene into triterpenoid precursors, which are essential components of the secondary metabolites found in <i>G. pentaphyllum</i>. To elucidate the role of <i>OSC</i> gene family members in the synthesis of gypenosides within <i>G. pentaphyllum</i>, this study undertook a comprehensive genome-wide identification and characterization of <i>OSC</i> genes within <i>G. pentaphyllum</i> and compared their expression levels across populations distributed over different geographical regions by both transcriptome sequencing and qRT-PCR experimental validation. The results identified a total of 11 members of the <i>OSC</i> gene family within the genome of <i>G. pentaphyllum</i>. These genes encode proteins ranging from 356 to 767 amino acids, exhibiting minor variations in their physicochemical properties, and are localized in peroxisomes, cytoplasm, plasma membranes, and lysosomes. All <i>GpOSC</i>s contain highly conserved DCTAE and QW sequences that are characteristic of the <i>OSC</i> gene family. A phylogenetic analysis categorized the <i>GpOSC</i>s into four distinct subfamilies. A cis-element analysis of the <i>GpOSC</i> promoters revealed a substantial number of abiotic stress-related elements, indicating that these genes may respond to drought conditions, low temperatures, and anaerobic environments, thus potentially contributing to the stress resistance observed in <i>G. pentaphyllum</i>. Expression analyses across different <i>G. pentaphyllum</i> populations demonstrated significant variability in <i>OSC</i> gene expression among geographically diverse samples of <i>G. pentaphyllum</i>, likely attributable to genetic variation or external factors such as environmental conditions and soil composition. These differences may lead to the synthesis of various types of gypenosides within geographically distinct <i>G. pentaphyllum</i> populations. The findings from this study enhance our understanding of both the evolutionary history of the <i>OSC</i> gene family in <i>G. pentaphyllum</i> and the biosynthetic mechanisms underlying triterpenoid compounds. This knowledge is essential for investigating molecular mechanisms involved in forming dammarane-type triterpenoid saponins as well as comprehending geographical variations within <i>G. pentaphyllum</i> populations. Furthermore, this research lays a foundation for employing plant genetic engineering techniques aimed at increasing gypenoside content.