Abstract
For strain improvement of Aspergillus oryzae, development of the transformation system is essential, wherein dominant selectable markers, including drug-resistant genes, are available. However, A. oryzae generally has a relatively high resistance to many antifungal drugs effective against yeasts and other filamentous fungi. In the course of the study, while investigating azole drug resistance in A. oryzae, we isolated a spontaneous mutant that exhibited high resistance to azole fungicides and found that pleiotropic drug resistance (PDR)-type ATP-binding cassette (ABC) transporter genes were upregulated in the mutant; their overexpression in the wild-type strain increased azole drug resistance. While deletion of the gene designated atrG resulted in increased azole susceptibility, double deletion of atrG and another gene (atrA) resulted in further azole hypersensitivity. Overall, these results indicate that the ABC transporters AtrA and AtrG are involved in azole drug resistance in A. oryzae.
Highlights
E (ABC) transporter genes were upregulated in the mutant; their overexpression in the wild-type strain increased azole drug resistance
We discovered that deletion of these ATP-binding cassette (ABC) transporter genes could lead to hyper-susceptibility to azole drugs, suggesting that AtrA and AtrG are involved in azole drug efflux and result in azole drug resistance in A. oryzae
Because several genes encoding ABC transporter families are found in the DNA database of the A. oryzae genome sequencing project [27], we first searched the A. oryzae EST database [28] to find the candidate ABC transporter genes that were seemingly expressed in the wild-type strain RIB40, and we found four independent EST clones homologous to the genes encoding fungal ABC transporters
Summary
E (ABC) transporter genes were upregulated in the mutant; their overexpression in the wild-type strain increased azole drug resistance. We observed that the upregulation of the genes encoding pleiotropic drug resistance (PDR)-type ABC transporters, designated AtrA and AtrG, possibly resulted in an increase in azole drug resistance in the mutant.
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