Genome-Wide Identification and Expression Profiling of the Oxidosqualene Cyclase Gene Family in Akebia trifoliata Across Fruit Development and Disease-Susceptibility Groups

Akebia trifoliata is an important Chinese traditional medicinal plant, and its abundant triterpenoids are the primary active medicinal components. However, the oxidosqualene cyclase (OSC) gene family responsible for constructing their triterpenoid skeletons has not yet been systematically characterized. In this study, nine AktOSC genes were identified genome-wide in A. trifoliata. Phylogenetic analysis revealed that most AktOSC members formed independent evolutionary subclades. Synteny and selective pressure analyses indicated that multiple duplication modes collectively contributed to the expansion of the AktOSC family, and all members were subjected to strong purifying selection. Sequence alignment showed that all members possess the characteristic motifs of the OSC family, whereas amino acid substitutions at critical active-site residues hinted at potential catalytic product diversity. Cis-acting element prediction revealed an abundance of environmental and phytohormone responsiveness elements within the AktOSC promoter regions. Expression profiling revealed that AktOSC genes exhibited distinct expression patterns across tissues, developmental stages, and disease-susceptibility groups. Finally, AktOSC8, which was specifically and highly expressed in the pericarp, was identified as a highest-priority candidate gene. Collectively, these findings provide essential foundational insights for further elucidating the mechanisms underlying triterpenoid biosynthesis and accumulation in A. trifoliata.