tRNA hypomodification facilitates 5-fluorocytosine resistance via cross-pathway control system activation in Aspergillus fumigatus.

Abstract

Increasing antifungal drug resistance is a major concern associated with human fungal pathogens like Aspergillus fumigatus. Genetic mutation and epimutation mechanisms clearly drive resistance, yet the epitranscriptome remains relatively untested. Here, deletion of the A. fumigatus tRNA-modifying isopentenyl transferase ortholog, Mod5, led to altered stress response and unexpected resistance against the antifungal drug 5-fluorocytosine (5-FC). After confirming the canonical isopentenylation activity of Mod5 by LC-MS/MS and Nano-tRNAseq, we performed simultaneous profiling of transcriptomes and proteomes to reveal a comparable overall response to 5-FC stress; however, a premature activation of cross-pathway control (CPC) genes in the knockout was further increased after antifungal treatment. We identified several orthologues of the A. nidulans Major Facilitator Superfamily (MFS) transporter nmeA as specific CPC-client genes in A. fumigatus. Overexpression of Mod5-target tRNATyrG{Psi}A in the {Delta}mod5 strain rescued select phenotypes but failed to reverse 5-FC resistance, whereas deletion of nmeA largely, but incompletely, reverted the resistance phenotype, implying additional relevant exporters. In conclusion, 5-FC resistance in the absence of Mod5 and i6A likely originates from multifaceted transcriptional and translational changes that skew the fungus towards premature CPC-dependent activation of antifungal toxic-intermediate exporter nmeA, offering a potential mechanism reliant on RNA modification to facilitate transient antifungal resistance.