ABC Transporters and Azole Susceptibility in Laboratory Strains of the Wheat Pathogen Mycosphaerella graminicola

Laboratory strains of Mycosphaerella graminicola with decreased susceptibilities to the azole antifungal agent cyproconazole showed a multidrug resistance phenotype by exhibiting cross-resistance to an unrelated chemical, cycloheximide or rhodamine 6G, or both. Decreased azole susceptibility was found to be associated with either decreased or increased levels of accumulation of cyproconazole. No specific relationship could be observed between azole susceptibility and the expression of ATP-binding cassette (ABC) transporter genes MgAtr1 to MgAtr5 and the sterol P450 14α-demethylase gene, CYP51. ABC transporter MgAtr1 was identified as a determinant in azole susceptibility since heterologous expression of the protein reduced the azole susceptibility of Saccharomyces cerevisiae and disruption of MgAtr1 in one specific M. graminicola laboratory strain with constitutive MgAtr1 overexpression restored the level of susceptibility to cyproconazole to wild-type levels. However, the level of accumulation in the mutant with an MgAtr1 disruption did not revert to the wild-type level. We propose that variations in azole susceptibility in laboratory strains of M. graminicola are mediated by multiple mechanisms.

对唑类抗真菌剂环丙唑醇（cyproconazole）敏感性降低的禾本科球腔菌（Mycosphaerella graminicola）实验室菌株，呈现出多药耐药表型：可对非相关化学物质放线菌酮（cycloheximide）、罗丹明6G（rhodamine 6G）或二者同时产生交叉耐药性。研究表明，该菌株的唑类敏感性降低与环丙唑醇的细胞积累水平升高或降低均存在相关性。未发现唑类敏感性与ATP结合盒（ATP-binding cassette, ABC）转运蛋白基因MgAtr1至MgAtr5以及固醇P450 14α-去甲基化酶基因CYP51的表达水平存在特定关联。ATP结合盒转运蛋白MgAtr1被确定为唑类敏感性的调控因子：该蛋白的异源表达可降低酿酒酵母（Saccharomyces cerevisiae）的唑类敏感性；在一株组成型过量表达MgAtr1的禾本科球腔菌实验室菌株中敲除MgAtr1，可使其对环丙唑醇的敏感性恢复至野生型水平。但该MgAtr1敲除突变体的环丙唑醇积累水平并未恢复至野生型状态。本研究提出，禾本科球腔菌实验室菌株的唑类敏感性差异由多种机制共同介导。