Neurospora crassa has four catalase genes—
cat-1,
cat-2,
cat-3, and
ctt-1/
cat-4.
cat-1 and
cat-3 encode two fungal-specific large-subunit catalases CAT-1 and CAT-3 normally produced in conidia and growing hyphae, respectively.
cat-2 encodes CAT-2 catalase-peroxidase normally produced in conidia.
ctt-1 (or
cat-4), of which expression was controlled by OS-2 MAP kinase (Noguchi et al., Fungal Genet. Biol.
44, 208–218), encodes a small-subunit catalase with unknown function. To clarify the contribution of OS-2 on the regulation of CAT-1, CAT-2, and CAT-3, we performed quantitative RT-PCR and in-gel catalase activity analyses. When the hyphae were treated with a fungicide (1 μg/ml fludioxonil) or subjected to an osmotic stress (1 M sorbitol),
cat-1 was strongly upregulated and CAT-1 was reasonably induced in the wild-type strain. Interestingly, fludioxonil caused not only the CAT-1 induction but also a remarkable CAT-3 decrease in the wild-type hyphae, implying of an abnormal stimulation of asexual differentiation. These responses were not observed in an
os-2 mutant hyphae, indicating an involvement of OS-2 in the
cat-1 expression; however,
os-2 was dispensable for the production of CAT-1 in conidia. In contrast, the expression of
cat-2 was significantly induced by heat shock (45°C) and that of
cat-3 was moderately stimulated by an oxidative stress (50 μg/ml methyl viologen) in both the wild-type strain and the
os-2 mutant, and corresponding enzyme activities were detected after the treatments. Although basal levels of transcription of
cat-1 and
cat-3 in an
os-2 mutant hyphae were a few-fold lower than in the wild-type hyphae, the
os-2 mutant exhibited a considerably lower levels of CAT-3 activity than the wild-type strain. These findings suggest that OS-2 MAP kinase regulated the expression of
cat-1 and
cat-3 transcriptionally, and probably that of
cat-3 posttranscriptionally, even though the presence of another regulatory system for each of these two genes is evident.
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