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Low intensity proton beam irradiation downregulates antioxidative protection in Aspergillus nidulans

ABSTRACT: The effect of a simulated solar particle event on the fungus Aspergillus nidulans was investigated by exposing surface cultures to a low intensity proton beam (10 pA) and comparing their transcriptomes with those of untreated cultures. Results showed upregulation of DNA repair, ribosome biogenesis, and protein ubiquitination genes, while glycolysis, and respiration genes were downregulated. Surprisingly, antioxidative enzyme genes were bulk-downregulated, increasing susceptibility to oxidative stress induced by menadione sodium bisulfite (MSB). Experiments with an oxidative stress-sensitive mutant and MSB-pretreated cultures suggested that oxidative stress protection was crucial for surviving proton radiation. Therefore, down-regulation of antioxidant enzyme genes was not an adaptive response, but probably a consequence of a disturbance in redox sensing caused by reductive pre-hydrated electrons from water radiolysis. These results shed light on the complex interaction between radiation stress and fungal responses, which could lead to the potential exploitation of the underlying mechanisms in real space environments.

ORGANISM(S): Aspergillus nidulans

PROVIDER: GSE294405 | GEO | 2026/03/04

REPOSITORIES: GEO

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	GSE294405_RPKM_space.xlsx	Xlsx

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Project description:Gene expression profiles of Escherichia coli K-12 W3110 were compared as a function of steady-state external pH. Cultures were grown with aeration to an optical density at 600 nm of 0.3 in potassium-modified Luria-Bertani medium buffered at pH 5.0, 7.0, and 8.7. For each of the three pH conditions, cDNA from RNA of five independent cultures was hybridized to Affymetrix E. coli arrays. Analysis of variance with a significance level of 0.001 resulted in 98% power to detect genes showing a twofold difference in expression. Normalized expression indices were calculated for each gene and intergenic region (IG). Differential expression among the three pH classes was observed for 763 genes and 353 IGs. Hierarchical clustering yielded six well-defined clusters of pH profiles, designated Acid High (highest expression at pH 5.0), Acid Low (lowest expression at pH 5.0), Base High (highest at pH 8.7), Base Low (lowest at pH 8.7), Neutral High (highest at pH 7.0, lower in acid or base), and Neutral Low (lowest at pH 7.0, higher at both pH extremes). Flagellar and chemotaxis genes were repressed at pH 8.7 (Base Low cluster), where the cell's transmembrane proton potential is diminished by the maintenance of an inverted pH gradient. High pH also repressed the proton pumps cytochrome o (cyo) and NADH dehydrogenases I and II. By contrast, the proton-importing ATP synthase F1Fo and the microaerophilic cytochrome d (cyd), which minimizes proton export, were induced at pH 8.7. These observations are consistent with a model in which high pH represses synthesis of flagella, which expend proton motive force, while stepping up electron transport and ATPase components that keep protons inside the cell. Acid-induced genes, on the other hand, were coinduced by conditions associated with increased metabolic rate, such as oxidative stress. All six pH-dependent clusters included envelope and periplasmic proteins, which directly experience external pH. Overall, this study showed that (i) low pH accelerates acid consumption and proton export, while coinducing oxidative stress and heat shock regulons; (ii) high pH accelerates proton import, while repressing the energy-expensive flagellar and chemotaxis regulons; and (iii) pH differentially regulates a large number of periplasmic and envelope proteins. Keywords: Steady State

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Low intensity proton beam irradiation downregulates antioxidative protection in Aspergillus nidulans

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