Osmoregulation and fungicide resistance: the Neurospora crassa os-2 gene encodes a HOG1 mitogen-activated protein kinase homologue.
Neurospora crassa osmosensitive (os) mutants are sensitive to high osmolarity and therefore are unable to grow on medium containing 4% NaCl. We found that os-2 and os-5 mutants were resistant to the phenylpyrrole fungicides fludioxonil and fenpiclonil. To understand the relationship between osmoregulation and fungicide resistance, we cloned the os-2 gene by using sib selection. os-2 encodes a putative mitogen-activated protein (MAP) kinase homologous to HOG1 and can complement the osmosensitive phenotype of a Saccharomyces cerevisiae hog1 mutant. We sequenced three os-2 alleles and found that all of them were null with either frameshift or nonsense point mutations. An os-2 gene replacement mutant also was generated and was sensitive to high osmolarity and resistant to phenylpyrrole fungicides. Conversely, os-2 mutants transformed with the wild-type os-2 gene could grow on media containing 4% NaCl and were sensitive to phenylpyrrole fungicides. Fludioxonil stimulated intracellular glycerol accumulation in wild-type strains but not in os-2 mutants. Fludioxonil also caused wild-type conidia and hyphal cells to swell and burst. These results suggest that the hyperosmotic stress response pathway of N. crassa is the target of phenylpyrrole fungicides and that fungicidal effects may result from a hyperactive os-2 MAP kinase pathway.
Zhang
Yan
Y
Syngenta Agribusiness Biotechnology Research Inc., Research Triangle Park, North Carolina 27709, USA.
Lamm
Randy
R
Pillonel
Christian
C
Lam
Stephen
S
Xu
Jin-Rong
JR
D004149:Dioxoles / Q000494:pharmacology*; D025141:Drug Resistance, Fungal; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005659:Fungicides, Industrial / Q000494:pharmacology*; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009492:Neurospora crassa / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D011758:Pyrroles / Q000494:pharmacology*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D014882:Water-Electrolyte Balance
D004149:Dioxoles; D005656:Fungal Proteins; D005659:Fungicides, Industrial; D011758:Pyrroles; D029701:Saccharomyces cerevisiae Proteins; C437165:fenpiclonil; C088589:HOG1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; C450461:os-2 protein, Neurospora crassa; C108339:fludioxonil