Involvement of OS-2 MAP kinase in regulation of the large-subunit catalases CAT-1 and CAT-3 in Neurospora crassa

Sep 27, 2007Genes & genetic systems

Role of OS-2 MAP kinase in controlling two main antioxidant enzymes in Neurospora crassa

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Abstract

The expression of the catalase gene cat-1 is strongly upregulated in Neurospora crassa hyphae treated with a fungicide.

CAT-1 and CAT-3 are large-subunit catalases produced in conidia and growing hyphae, respectively.
CAT-2 is a catalase-peroxidase normally produced in conidia.
Treatment with fludioxonil induces CAT-1 while decreasing CAT-3 levels, suggesting an abnormal shift in asexual differentiation.
OS-2 MAP kinase is involved in the regulation of cat-1 expression but is not necessary for CAT-1 production in conidia.
Heat shock significantly induces cat-2 expression, while oxidative stress moderately stimulates cat-3 in both wild-type and os-2 mutant strains.
The os-2 mutant exhibits lower transcription of cat-1 and cat-3, as well as reduced CAT-3 activity compared to the wild-type strain.

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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 mug/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 degrees C) and that of cat-3 was moderately stimulated by an oxidative stress (50 microg/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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Involvement of OS-2 MAP kinase in regulation of the large-subunit catalases CAT-1 and CAT-3 in Neurospora crassa

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