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. 2015 Jun 27;16(1):478.
doi: 10.1186/s12864-015-1705-z.

Core oxidative stress response in Aspergillus nidulans

Tamás Emri  1 , Vera Szarvas  2 , Erzsébet Orosz  3 , Károly Antal  4 , HeeSoo Park  5 , Kap-Hoon Han  6 , Jae-Hyuk Yu  7 , István Pócsi  8
Affiliations

Core oxidative stress response in Aspergillus nidulans

Tamás Emri et al. BMC Genomics. .

Abstract

Background: The b-Zip transcription factor AtfA plays a key role in regulating stress responses in the filamentous fungus Aspergillus nidulans. To identify the core regulons of AtfA, we examined genome-wide expression changes caused by various stresses in the presence/absence of AtfA using A. nidulans microarrays. We also intended to address the intriguing question regarding the existence of core environmental stress response in this important model eukaryote.

Results: Examination of the genome wide expression changes caused by five different oxidative stress conditions in wild type and the atfA null mutant has identified a significant number of stereotypically regulated genes (Core Oxidative Stress Response genes). The deletion of atfA increased the oxidative stress sensitivity of A. nidulans and affected mRNA accumulation of several genes under both unstressed and stressed conditions. The numbers of genes under the AtfA control appear to be specific to a stress-type. We also found that both oxidative and salt stresses induced expression of some secondary metabolite gene clusters and the deletion of atfA enhanced the stress responsiveness of additional clusters. Moreover, certain clusters were down-regulated by the stresses tested.

Conclusion: Our data suggest that the observed co-regulations were most likely consequences of the overlapping physiological effects of the stressors and not of the existence of a general environmental stress response. The function of AtfA in governing various stress responses is much smaller than anticipated and/or other regulators may play a redundant or overlapping role with AtfA. Both stress inducible and stress repressive regulations of secondary metabolism seem to be frequent features in A. nidulans.

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Figures

Fig. 1
Fig. 1
Comparison of the stress sensitivities of control and ΔatfA Aspergillus nidulans strains. Plates were point-inoculated with freshly grown conidia (105 conidia in 5 μl aliquots of 0.9 % NaCl, 0.01 % Tween 80) and were incubated at 37 °C for 5 d (Yin et al., 2013 [63]). All assays were carried out in triplicates, and representative photos are presented here. The stress sensitivites of the ΔatfA strain were always higher than those of the control at any concentrations of the oyidative stress generating agents tested. In contrast, there was no difference between the relative growths of the mutant and control strains when exposed to NaCl. The employed stressor concentrations were: tBOOH: 0.8 mM, H2O2: 6.0 mM, MSB: 0.12 mM, diamide: 2.0 mM and NaCl: 0.6 M. Representative photos are presented
Fig. 2
Fig. 2
Comparison of transcriptome data sets of stress-exposed control and ΔatfA strains. Pairwise similarities between transcriptome profiles were characterized by absolute correlations of normalized microarray data presented in Additional file 4: Table S4, and are summarized using agglomerative hierarchical cluster analysis with complete linkage
Fig. 3
Fig. 3
Cross adaptations observed in the control and ΔatfA strains. The control (white columns) and ΔatfA (grey columns) strains were pre-cultured for 0.5 h in the presence of various stress initiating agents as indicated. Following pre-treatments, fungi were exposed to 0.18 mM MSB (Part a) or 1.0 M NaCl (Part b) in fresh culture media. All cultures were incubated for 18 h, and increases in the dry cell mass (DCM) values were determined, which are presented here as means ± S.D. values (n = 3). Untreated cultures were not subjected to stress treatments at all meanwhile control cultures were exposed to MSB and NaCl without stress pre-treatments. *Significant differences in comparison to control cultures calculated by Student’s t-test (p < 0.05, n = 3)
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