ATF-1 transcription factor regulates the expression of ccg-1 and cat-1 genes in response to fludioxonil under OS-2 MAP kinase in Neurospora crassa

The ATF/CREB family transcriptional factors are regulated by stress-activated MAP kinase in yeast. The disruptants of the atf-1 gene, which encodes an ATF/CREB family transcriptional factor, were isolated and characterized in Neurospora crassa. The characteristic phenotypes in the os-2 MAP kinase strain, such as osmotic sensitivity and fludioxonil resistance, were not observed in the Δatf-1 strain; however, like the os-2 strain, up-regulation of the catalase gene cat-1 and the clock-controlled gene ccg-1 by treatment with fludioxonil (1 μg/mL) or 4% NaCl was almost completely abolished in the Δatf-1 strain. A gel shift assay indicated that ATF-1 bound to the cat-1 and ccg-1 promoters probably through the CRE motifs. The enzyme activity of large-subunit catalase CAT-1, the major conidial catalase, was not detected in the Δatf-1 strain, suggesting that the production of CAT-1 during formation of conidia is largely dependent on ATF-1. Among 11 clock-controlled genes, the expression of ccg-1, ccg-9, ccg-13, and ccg-14 was induced by fludioxonil in an OS-2-dependent manner; however, induction of ccg-13 and ccg-14 was observed in the Δatf-1 strain, suggesting the existence of another transcription factor regulated by OS-2. The homozygous cross between the Δatf-1 strains produced perithecia and ascospores; however, their ascospores never germinated. These findings suggest that ATF-1 acts as one of the transcriptional factors downstream of the OS-2 MAP kinase and probably regulates some genes involved in conidiation, circadian rhythm, and ascospore maturation in N. crassa.