Enhancement of Triterpenoid Synthesis in Antrodia cinnamomea through Homologous Expression of the Key Synthetic Pathway Genes AcLSS and AcERG4

Antrodia cinnamomea (AC), a rare fungus endemic to Taiwan, contains high levels of various secondary metabolites, notably triterpenoids, having useful medicinal and pharmacological properties. Techniques for increasing the production of AC triterpenoids (ACT) for medicinal purposes are a high research priority. We measured and compared the biomass and ACT content of AC mycelia under various liquid fermentation culture conditions. Relative gene expression levels of ten enzymes involved in the mevalonate (MVA) pathway and subsequent group modification pathway were determined, and correlation analysis was performed to evaluate the roles of these enzyme genes in ACT synthesis. Two representative genes encoding the enzymes lanosterol synthase (AcLSS) and sterol C-24 reductase (AcERG4), whose activity is closely associated with ACT content, were selected for homologous expression. AcLSS and AcERG4 were separately linked to plasmid pCT74, and transformed into prepared AC protoplasts to obtain two recombinant strains, termed RpLSS and RpERG4, by polyethylene glycol (PEG)-CaCl2-mediated protoplast transformation. Upregulated expression levels of AcLSS and AcERG4 (1.78- and 1.41-fold, respectively) were associated with significantly higher (1.82- and 1.37-fold, respectively) ACT content in the recombinant strains in comparison with the wild-type. Our findings provide a theoretical and practical basis for the enhancement of ACT production using homologous expression techniques.