title: Multiple mechanisms account for variation in base-line sensitivity to azole fungicides in field isolates of Mycosphaerella graminicola.
abstract: Molecular mechanisms that account for variation in base-line sensitivity to azole fungicides were examined in a collection of twenty field isolates, collected in France and Germany, of the wheat pathogen Mycosphaerella graminicola (Fuckel) Schroeter. The isolates tested represent the wide baseline sensitivity to the azole fungicide tebuconazole described previously. The isolates were cross-sensitive to other azoles tested, such as cyproconazole and ketoconazole, but not to unrelated chemicals like cycloheximide, kresoxim-methyl or rhodamine 6G. Progenies from a genetic cross between an isolate with an intermediate and a high sensitivity to azoles displayed a continuous range of phenotypes with respect to cyproconazole sensitivity, indicating that variation in azole sensitivity in this haploid organism is polygenic. The basal level of expression of the ATP-binding cassette transporter genes MgAtr1-MgAtr5 from Mgraminicola significantly varied amongst the isolates tested, but no clear increase in the transcript level of a particular MgAtr gene was found in the less sensitive isolates. Cyproconazole strongly induced expression of MgAtr4, but no correlation between expression levels of this gene and azole sensitivity was observed. One isolate with intermediate sensitivity to azoles over-expressed CYP51, encoding cytochrome P450 sterol 14alpha-demethylase from M graminicola. Isolates with a low or high sensitivity to azoles were tested for accumulation of cyproconazole, but no clear correlation between reduced accumulation of the fungicide in mycelium and sensitivity to azoles was observed. Therefore, differences in accumulation cannot account exclusively for the variation in base-line sensitivity of the isolates to azoles. The results indicate that multiple mechanisms account for differences in base-line sensitivity to azoles in field isolates of M graminicola.
authors.affiliation: Laboratory of Phytopathology, Department of Plant Sciences, Wageningen University, PO Box 8025, Binnenhaven 5, 6709 PD Wageningen, The Netherlands.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Stergiopoulos
authors.forename: Johannes G M
authors.initials: JG
authors.lastname: van Nistelrooy
authors.forename: Gert H J
authors.initials: GH
authors.lastname: Kema
authors.forename: Maarten A
authors.initials: MA
authors.lastname: De Waard
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D001203:Ascomycota / Q000187:drug effects* / Q000235:genetics; D001393:Azoles / Q000633:toxicity*; D002250:Carbon Radioisotopes; D003433:Crosses, Genetic; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005659:Fungicides, Industrial / Q000378:metabolism / Q000633:toxicity*; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D007654:Ketoconazole / Q000378:metabolism / Q000633:toxicity; D008826:Microbial Sensitivity Tests / Q000379:methods; D014230:Triazoles / Q000378:metabolism / Q000633:toxicity
chemical_list: D018528:ATP-Binding Cassette Transporters; D001393:Azoles; D002250:Carbon Radioisotopes; D005656:Fungal Proteins; D005659:Fungicides, Industrial; D014230:Triazoles; C087114:tebuconazole; C093628:cyproconazole; D003577:Cytochrome P-450 Enzyme System; D007654:Ketoconazole