Production of the harmful carcinogenic aflatoxins by
Aspergillus parasiticus and
Aspergillus flavus has been postulated to be a mechanism to relieve oxidative stress. The
msnA gene of
A. parasiticus and
A. flavus is the ortholog of
Saccharomyces cerevisiae MSN2 that is associated with multi-stress response. Compared to wild type strains, the
msnA deletion (∆msnA) strains of
A. parasiticus and
A. flavus exhibited retarded colony growth with increased conidiation. The ∆msnA strains also produced slightly higher amounts of aflatoxins and elevated amounts of kojic acid on mixed cereal medium. Microarray assays showed that expression of genes encoding oxidative stress defense enzymes,
i.e., superoxide dismutase, catalase, and cytochrome c peroxidase in
A. parasiticus ∆msnA, and the catalase A gene in
A. flavus ∆msnA, was up-regulated. Both
A. parasiticus and
A. flavus ∆msnA strains produced higher levels of reactive oxygen species (ROS), and ROS production of
A. flavus msnA addback strains was decreased to levels comparable to that of the wild type
A. flavus. The
msnA gene appears to be required for the maintenance of the normal oxidative state. The impairment of
msnA resulted in the aforementioned changes, which might be used to combat the increased oxidative stress in the cells.
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