Multidrug Resistance in Botrytis cinerea Associated with Decreased Accumulation of the Azole Fungicide Oxpoconazole and Increased Transcription of the ABC Transporter Gene BcatrD

Azole-resistant mutants of Botrytis cinerea have a multidrug resistance phenotype since they exhibit cross-resistance to unrelated chemicals. These mutants also display resistance to the new azole fungicide oxpoconazole. Resistance to oxpoconazole is associated with decreased accumulation of the fungicide, which is the result of energy-dependent efflux mediated by fungicide transporters. The ATP-binding cassette (ABC) transporter BcatrB (B. cinerea ABC transporter B), involved in efflux of phenylpyrrole fungicides, has no major role in efflux of oxpoconazole since accumulation of the fungicide by a replacement mutant of BcatrB showed a transient accumulation pattern similar to that of the wild-type isolate. The putative role of 10 additional ABC and 3 Major facilitator superfamily transporters in efflux of oxpoconazole was investigated by expression analysis of the corresponding genes. The basal transcription level of BcatrD in germlings of B. cinerea was correlated with the resistance level of two azole-resistant mutants. A short treatment of germlings with the azole fungicides oxpoconazole, prochloraz, and tebuconazole enhanced transcript levels of BcatrD in a wild-type isolate. Transcript levels induced by these fungicides in azole-resistant mutants also correlated with resistance levels. We propose that BcatrD is the ABC transporter that plays a role in azole sensitivity and azole resistance of B. cinerea. Expression of BcatrD is also induced by treatment of germlings with the dicarboximide fungicide iprodione, the benzimidazole fungicide carbendazim, and the antibiotic cycloheximide, suggesting that this gene indeed plays a role in multidrug resistance to fungicides.