title: Characterization of laboratory mutants of Venturia inaequalis resistant to the strobilurin-related fungicide kresoxim-methyl.
abstract: Several agricultural fungicides related to the antifungal strobilurins act as inhibitors of respiration by binding to mitochondrial cytochrome b. Two types of laboratory mutants resisting higher doses of the strobilurin-related inhibitor kresoxim-methyl were characterized for Venturia inaequalis, the causal agent of apple scab. Selection of mutagenized conidia by kresoxim-methyl yielded mutants altered in the expression of alternative respiration during the stage of conidia germination. Cytochrome b sequences were not affected in the respective mutants. Selection of conidia on media containing the alternative oxidase inhibitor salicylhydroxamic acid in addition to kresoxim-methyl yielded a highly resistant mutant distinguished by a G143A exchange in cytochrome b. The status of mitochondrial cytochrome b genes remained heteroplasmic, and mitochondria containing wild-type cytochrome b returned to high frequencies during cultivation on inhibitor-free medium. However, continuation of the selection process led to a more pronounced replacement of sensitive by mutated mitochondria. The G143A mutation of cytochrome b causing resistance of V. inaequalis to a strobilurin-related inhibitor has been reported previously for mouse mitochondria; and a permanent G143A exchange rendering naturally resistant mitochondria has been reported for the strobilurin-producing basidiomycete Mycena galopoda and for the sea urchin Paracentrotus lividus. At the corresponding position, alanine was also present in chloroplast cytochrome b6 exhibiting low binding of strobilurin-related inhibitors. The mutation of cytochrome b reported here for V. inaequalis describes the first example of a mutation in filamentous ascomycetes and is part of an assessment of resistance risks inherent to strobilurin fungicides.
authors.affiliation: Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456, USA.
authors.forename: D
authors.initials: D
authors.lastname: Zheng
authors.forename: G
authors.initials: G
authors.lastname: Olaya
authors.forename: W
authors.initials: W
authors.lastname: Köller
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000187:drug effects / Q000235:genetics*; D001483:Base Sequence; D001542:Benomyl / Q000494:pharmacology*; D017931:DNA Primers / Q000737:chemistry; D004271:DNA, Fungal / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics*; D005659:Fungicides, Industrial / Q000494:pharmacology*; D005786:Gene Expression Regulation; D005800:Genes, Fungal; D008928:Mitochondria / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D004271:DNA, Fungal; D004272:DNA, Mitochondrial; D005659:Fungicides, Industrial; D001542:Benomyl