Location: Food and Feed Safety ResearchTitle: VeA is associated with the response to oxidative stress in the aflatoxin producer Aspergillus flavus Author
|Harris Coward, Pamela|
Submitted to: Eukaryotic Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2014
Publication Date: 8/20/2014
Citation: Baidya, S., Duran, R.M., Lohmar, J.M., Harris-Coward, P.Y., Cary, J.W., Hong, S.-Y., Roze, L.V., Linz, J.E., Calvo, A.M. 2014. VeA is associated with the response to oxidative stress in the aflatoxin producer Aspergillus flavus. Eukaryotic Cell. 13(8):1095-1103. Interpretive Summary: This work describes experiments that have been conducted in an effort to better understand the genetic mechanisms that control aflatoxin production and growth and development in Aspergillus flavus. Aflatoxins are toxic and carcinogenic compounds often produced by the fungi, Aspergillus flavus during growth on crops such as corn, peanuts, cottonseed, and treenuts. Because of the potential health risks, aflatoxin contamination of food and feed crops is also of great economic importance to farmers who cannot sell their crops due to strict domestic and international regulatory guidelines with regards to aflatoxin contamination. Survival of fungi in the field and on plants depends on their ability to respond to environmental stresses. Exposure of fungi to osmotic or oxidative stress can result in growth inhibition. Many fungi have evolved complex signaling pathways needed to respond the osmotic and oxidative stress. This study revealed that while the osmotic stress response is only slightly affected by the master regulator veA, this gene, also known to control morphological development and secondary metabolism in A. flavus and other fungal species, has a profound effect on the oxidative stress response in A. flavus. We found that the expression of A.flavus genes involved in the oxidative stress signaling pathway is regulated by veA. Furthermore, analyses of the effect of VeA protein on the promoters of oxidative stress response genes, cat1 and trxB, indicate that the presence of VeA alters DNA-protein complex formation. We can now use what we have learned from these studies to try and identify other A. flavus genes that are part of the VeA control circuit and use this knowledge to aid in unraveling the mechanisms responsible for production of aflatoxin and other A. flavus toxins. This in turn will help in devising strategies for eliminating fungal toxin contamination of food and feed crops.
Technical Abstract: Survival of fungal species depends on the ability of these organisms to respond to environmental stresses. Osmotic stress or high levels of reactive oxygen species (ROS) can cause stress in fungi resulting in growth inhibition. Both eukaryotic and prokaryotic cells have developed numerous mechanisms to counteract and survive the stress under the presence of ROS. In many fungi, the HOG signaling pathway is crucial for the oxidative stress response as well as for osmotic stress response. This study revealed that while the osmotic stress response is only slightly affected by the master regulator veA, this gene, also known to control morphological development and secondary metabolism in numerous fungal species, has a profound effect on the oxidative stress response in the aflatoxin-producing fungus Aspergillus flavus.We found that the expression of A. flavus homolog genes involved in the HOG signaling pathway is regulated by veA. Deletion of veA resulted in a reduction in transcription levels of oxidative stress response genes after exposure to hydrogen peroxide. Furthermore, analyses of the effect of VeA on the promoters of cat1 and trxB indicate that presence of VeA alters DNA-protein complex formation. This is particularly notable in the cat1 promoter, where the absence of VeA results in abnormally stronger complex formation with reduced cat1 expression and more sensitivity to ROS in a veA deletion mutant, suggesting that VeA might prevent binding of negative transcription regulators to the cat1 promoter. Our study also revealed that veA positively influences the expression of the transcription factor gene atfB, and that normal formation of DNA-protein complexes in the cat1 promoter was dependent on AtfB.