RTA-like proteins regulate azole susceptibility by affecting the expression of the oxidoreductase gene oxrA in Aspergillus fumigatus

Aspergillus fumigatus, a saprophytic fungus and the principal etiologic agent of aspergillosis, is increasingly implicated in drug-resistant infections, posing challenges to clinical management. RTA-like proteins, a distinctive class of transmembrane fungal proteins, are involved in several stress responses. Nonetheless, their role in fungal azole resistance is yet to be determined. Transcriptomic studies performed in this investigation revealed that azole stimulation significantly upregulates the expression of RTA-like proteins in A. fumigatus. Phenotypic analyses indicated that relative to the wild-type strain, the Δrta1, Δrta5 and Δrta7 mutants exhibited increased sensitivity to antifungal agents, including azoles and amphotericin B (AmB). RNA sequencing and real-time quantitative polymerase chain reaction indicated a significant upregulation of the oxidoreductase gene oxrA, which is integral to the oxidative stress response, in the Δrta1, Δrta5 and Δrta7 mutants. Furthermore, the oxrA overexpression strain (OE::oxrA) displayed increased tolerance to oxidative stress, yet paradoxically, it also showed a considerable hike in sensitivity to azole and AmB. This heightened drug sensitivity was correlated with the downregulation of most drug efflux pump genes. In conclusion, the RTA-like proteins Rta1, Rta5 and Rta7 possibly modulate azole susceptibility in A. fumigatus by regulating oxrA expression, subsequently affecting the transcription of drug efflux pump genes. As proteins specific to fungi, members of the RTA family are promising targets for the development of novel antifungal therapeutics.