Aspergillus flavus is the second most significant pathogenic cause of invasive aspergillosis; however, its emergence risks and mechanisms of voriconazole (VRC) resistance have not yet been elucidated in detail. Here, we demonstrate that repeated exposure of A. flavus to subinhibitory concentrations of VRC in vitro causes the emergence of a VRC-resistant mutant with a novel resistance mechanism. The VRC-resistant mutant shows a MIC of 16 μg/ml for VRC and of 0.5 μg/ml for itraconazole (ITC). Whole-genome sequencing analysis showed that the mutant possesses a point mutation in yap1, which encodes a bZIP transcription factor working as the master regulator of the oxidative stress response, but no mutations in the cyp51 genes. This point mutation in yap1 caused alteration of Leu558 to Trp (Yap1Leu558Trp) in the putative nuclear export sequence in the carboxy-terminal cysteine-rich domain of Yap1. This Yap1Leu558Trp substitution was confirmed as being responsible for the VRC-resistant phenotype, but not for that of ITC, by the revertant to Yap1wild type with homologous gene replacement. Furthermore, Yap1Leu558Trp caused marked upregulation of the atrF ATP-binding cassette transporter, and the deletion of atrF restored susceptibility to VRC in A. flavus These findings provide new insights into VRC resistance mechanisms via a transcriptional factor mutation that is independent of the cyp51 gene mutation in A. flavus.
Keywords: Aspergillus flavus; atrF; azole resistance; voriconazole; yap1.
Copyright © 2018 American Society for Microbiology.