Characterization of mutations in the two-component histidine kinase geneAbNIK1fromAlternaria brassicicolathat confer high dicarboximide and phenylpyrrole resistance.

Highly iprodione- and fludioxonil-resistant field and laboratory isolates ofA. brassicicolawere found to be either moderately sensitive or tolerant to osmotic stress.AbNIK1, a two-component histidine kinase gene, was isolated from a fungicide-sensitive strain. The predicted protein possessed the six tandem amino acid repeats at the N-terminal end, which is a landmark of osmosensor histidine kinases from filamentous fungi. A comparison of the nucleic acid sequences of theAbNIK1gene from fungicide-sensitive and fungicide-resistant isolates revealed the presence of mutations in six of the seven resistant strains analyzed. Null mutants were all found to be moderately sensitive to osmotic stress, indicating that they are similar toNeurospora crassaType Ios-1mutants. Only one mutation, corresponding to a single amino acid change within the H-box of the kinase domain, was found in an osmotolerant strain. These results suggest that AbNIK1p participates in osmoregulation and that expression of the fully functional enzyme is essential for dicarboximide and phenylpyrrole antifungal activities. [ABSTRACT FROM AUTHOR]