Loss of msnA, a Putative Stress Regulatory Gene, in Aspergillus parasiticus and Aspergillus flavus Increased Production of Conidia, Aflatoxins and Kojic Acid

Perng-Kuang Chang,Russell J Molyneux,Leslie L Scharfenstein,Jiujiang Yu,Noreen Mahoney,Meng Luo,Robert L Brown,Bruce C Campbell

doi:10.3390/toxins3010082

Abstract

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.

Highlights

In nature all living organisms react to unfavorable environmental conditions, such as high temperature, osmotic shock, oxidative damage and nutrient depletion via complex regulatory networks.These specific responses usually result from induction of a set of stress-associated genes whose expression is controlled by a common transcription factor
Msn2p mediates expression of a number of genes that are induced by stress conditions by binding to STRE motifs, CCCCT, which are located in the promoters of the regulated genes [2,3]
We investigated the role of msnA in two morphologically distinct A. parasiticus strains and an L-strain A. flavus isolate

Summary

Introduction

In nature all living organisms react to unfavorable environmental conditions, such as high temperature, osmotic shock, oxidative damage and nutrient depletion via complex regulatory networks. These specific responses usually result from induction of a set of stress-associated genes whose expression is controlled by a common transcription factor. Msn2p mediates expression of a number of genes that are induced by stress conditions by binding to STRE (stress response element) motifs, CCCCT, which are located in the promoters of the regulated genes [2,3]. In. Trichoderma atrovirde the expression of the MSN2 ortholog seb (stress response element binding) was increased under osmotic stress conditions [4]. Seb functions to up-regulate the glycerol dehydrogenase gene (gld1) whose product, Gld, is required for glycerol biosynthesis to alleviate osmotic stress [5]

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Conclusion