Characterization of mutations in the two-component histidine kinase gene that confer fludioxonil resistance and osmotic sensitivity in the os-1 mutants of Neurospora crassa
N. Ochiai et al., Characterization of mutations in the two-component histidine kinase gene that confer fludioxonil resistance and osmotic sensitivity in the os-1 mutants of Neurospora crassa, PEST MAN SC, 57(5), 2001, pp. 437-442
Osmotic-sensitive (os-1) mutant alleles in Neurospora crassa exhibit resist
ance to dicarboximides, aromatic hydrocarbons and phenylpyrroles. We have p
reviously reported that the os-1 mutants can be classified into two groups
based on their resistance to fungicides and osmotic stress: type I, which a
re highly resistant to iprodione and fludioxonil but moderately sensitive t
o osmotic stress, and type II, which are highly sensitive to osmotic stress
but moderately resistant to fungicides. To explain the mechanism of resist
ance to these fungicides, we cloned and sequenced the mutant os-1 genes tha
t encode putative osmo-sensing histidine kinase. Within the os-1 gene produ
ct (Os1p), the type I strains, NM233t and Y256M209, carried a stop codon at
amino acid position 308 and a frameshift at amino acid position 294, respe
ctively. These mutation sites were located on the upstream of histidine kin
ase and the response regulator domains of Os1p, strongly suggesting that ty
pe I strains are null mutants. The null mutants, NM233t and Y256M209, were
highly resistant to iprodione and fludioxonil; thus Os1p is essential for t
hese fungicides to express their antifungal activity. The amino acid change
s in Os1p, (625)Pro from Leu, (578)Val from Ala, and (580)Arg from Gly were
found in the type II strains, M16, M155-1 and P5990, respectively. Os1p is
novel in having six tandem repeats of 90 amino acids in the N terminal. Ea
ch amino acid change of the type II strains was located on the fifth unit o
f six tandem repeats. Type II strains with single amino acid changes were m
ore sensitive to osmotic stress than the null mutants (type I), indicating
that the amino acid repeats of Os1p were responsible for an important funct
ion in osmo-regulation. (C) 2001 Society of Chemical Industry.