An efficient gene targeting system using Δku80and functional analysis of Cyp51A inTrichophyton rubrum

Trichophyton rubrum is one of the most frequently isolated fungi in patients with dermatophytosis. Despite its clinical significance, the molecular mechanisms of drug resistance and pathogenicity of T. rubrum remain to be elucidated because of the lack of genetic tools, such as efficient gene targeting systems. In this study, we generated a T. rubrum strain that lacks the nonhomologous end-joining-related gene ku80 (Δ ku80 ) and then developed a highly efficient genetic recombination system with gene targeting efficiency that was 46 times higher than that using the wild-type strain. Cyp51A and Cyp51B are 14-α-lanosterol demethylase isozymes in T. rubrum that promote ergosterol biosynthesis and are the targets of azole antifungal drugs. The expression of cyp51A mRNA was induced by the addition of the azole antifungal drug efinaconazole, whereas no such induction was detected for cyp51B , suggesting that Cyp51A functions as an azole-responsive Cyp51 isozyme. To explore the contribution of Cyp51A to susceptibility to azole drugs, the neomycin phosphotransferase ( nptII ) gene cassette was inserted into the cyp51A 3′-UTR region of Δ ku80 to destabilize the mRNA of cyp51A . In this mutant, although the expression level of cyp51A mRNA was comparable to that of the parent strain, the induction of cyp51A mRNA expression by efinaconazole was diminished. The minimum inhibitory concentration for several azole drugs of this strain was reduced, suggesting that dermatophyte Cyp51A contributes to the tolerance for azole drugs. These findings suggest that an efficient gene targeting system using Δ ku80 in T. rubrum is applicable for analyzing genes encoding drug targets. Key Points A novel gene targeting system using Δ ku80 strain was established in T. rubrum Cyp51A in T. rubrum responds to the azole antifungal drug efinaconazole Cyp51A contributes to azole drug tolerance in T. rubrum