Two divergent catalase genes are differentially regulated during Aspergillus nidulans development and oxidative stress

Abstract

Catalases are ubiquitous hydrogen peroxide-detoxifying enzymes that are central to the cellular antioxidant response. Of two catalase activities detected in the fungus Aspergillus nidulans, the catA gene encodes the spore-specific catalase A (CatA). Here we characterize a second catalase gene, identified after probing a genomic library with catA, and demonstrate that it encodes catalase B. This gene, designated catB, predicts a 721-amino-acid polypeptide (CatB) showing 78% identity to an Aspergillus fumigatus catalase and 61% identity to Aspergillus niger CatR. Notably, similar levels of identity are found when comparing CatB to Escherichia coli catalase HPII (43%), A. nidulans CatA (40%), and the predicted peptide of a presumed catA homolog from A. fumigatus (38%). In contrast, the last two peptides share a 79% identity. The catalase B activity was barely detectable in asexual spores (conidia), disappeared after germination, and started to accumulate 10 h after spore inoculation, throughout growth and conidiation. The catB mRNA was absent from conidia, and its accumulation correlated with catalase activity, suggesting that catB expression is regulated at the transcription level. In contrast, the high CatA activity found in spores was lost gradually during germination and growth. In addition to its developmental regulation, CatB was induced by H 2 O 2 , heat shock, paraquat, or uric acid catabolism but not by osmotic stress. This pattern of regulation and the protective role against H 2 O 2 offered by CatA and CatB, at different stages of the A. nidulans life cycle, suggest that catalase gene redundancy performs the function of satisfying catalase demand at the two different stages of metabolic and genetic regulation represented by growing hyphae versus spores. Alternative H 2 O 2 detoxification pathways in A. nidulans were indicated by the fact that catA/catB double mutants were able to grow in substrates whose catabolism generates H 2 O 2 .

Characterization of the bZip-Type Transcription Factor NapA with Reference to Oxidative Stress Response inAspergillus nidulans

“…The catB gene encoding a catalase is known to act as a major scavenger against H 2 O 2 during the hyphal growth of A. nidulans. 8) As expected, transcription of catB-mRNA was markedly enhanced in the wild-type background in response to H 2 O 2 , with which A. nidulans cells grown in liquid MM2G medium were treated. Such induction of catBmRNA was severely attenuated not only in ÁsskA and ÁsrrA, but also in ÁnapA.…”

Deletion Analysis of the Catalase-Encoding Gene (catB) Promoter fromAspergillus oryzae

“…It has beeen reported that the HSE and its binding protein heat shock transcription factor are highly conserved from yeast to humans. [19][20][21] It is well known that heat shock and hydrogen peroxide induces catalase gene expression in Aspergilli 5,[22][23][24] and other species, [6][7][8]25) and that each catalase gene promoter has regulatory element for stress response. But the regulatory elements are different in species.…”

“…NS indicates nonspecific competitor. Either 10 pmol (lanes 3,6,9,12,15,20,23,26,29, and 32), 5 pmol (lanes 4, 7, 10, 13, 16, 21, 24, 27, and 30), or 1 pmol (lanes 5,8,11,14,17,22,25,28, and 31) of the competitors were added. SB and FP indicate the shifted band and the free probe, respectively.…”

The SskA and SrrA Response Regulators Are Implicated in Oxidative Stress Responses of Hyphae and Asexual Spores in the Phosphorelay Signaling Network ofAspergillus nidulans

“…In A. nidulans, four catalases (CatA to D) have been identified. [37][38][39][40] For both ÁsskA and ÁsrrA cells grown in MM2G liquid medium (i.e., under hyphal growth conditions), the expression of these four catalase genes was examined in response to H 2 O 2 (5 mM), which was applied externally to the medium (Fig. 5).…”