Characterization of a Group of 2,3-Oxidosqualene Cyclase Genes Involved in the Biosynthesis of Diverse Triterpenoids of Perilla frutescens

Perilla frutescens (L.), a traditional edible and medicinal crop, contains diverse triterpenes with multiple pharmacological properties. However, the biosynthesis of triterpenes in perilla remains rarely revelation. In this study, nine putative 2,3-oxidosqualene cyclase (OSC) genes (PfOSC1-9) were screened from the P. frutescens genome and functionally characterized by heterologous expression. Camelliol C, a triterpenol with pharmacological effect, was first identified as abundant in perilla seeds, and the camelliol C synthase (PfOSC7) was first identified in P. frutescens utilizing a yeast system. In addition, PfOSC2, PfOSC4, and PfOSC9 were identified as cycloartenol, lupeol, and β-amyrin synthase, respectively. Molecular docking and site-directed mutagenesis revealed that changes in Leu253 of PfOSC4, Ala480 of PfOSC7, and Trp257 of PfOSC9 might lead to variations of catalytic specificity or efficiency. These results will provide key insights into the biosynthetic pathways of triterpenoids and have great significance for germplasm breeding in P. frutescens.