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Title: The master transcription factor mtfA governs aflatoxin production, morphological development, and pathogenicity in the fungus Aspergillus flavus

item ZHUANG, ZHENHONG - Northern Illinois University
item LOHMAR, JESSICA - Northern Illinois University
item SATTERLEE, TIMOTHY - Northern Illinois University
item Cary, Jeffrey
item CALVO, ANA - Northern Illinois University

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2016
Publication Date: 1/20/2016
Citation: Zhuang, Z., Lohmar, J.M., Satterlee, T., Cary, J.W., Calvo, A.M. 2016. The master transcription factor mtfA governs aflatoxin production, morphological development, and pathogenicity in the fungus Aspergillus flavus. Toxins. 8(1):29. doi:10.3390/toxins8010029.

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. We have succeeded identifying a gene, designated veA, from A. flavus that when inactivated stops the fungus from producing aflatoxin and also structures known as sclerotia that help the fungus to survive in the field under adverse conditions. In addition, this study showed that veA also controls the production of two other known toxins in A. flavus, cyclopiazonic acid and aflatrem. 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: Aspergillus flavus produces a variety of toxic secondary metabolites, among them the aflatoxins (AFs) are the most well-known. These compounds are highly mutagenic and carcinogenic, particularly AFB1. A. flavus is capable of colonizing economically important crops contaminating them with AFs. Molecular genetic studies in A. flavus could provide novel targets to potentially design strategies to reduce the negative impact of AF contamination of our food supply. In the current study, we investigated the role of the master transcription factor gene mtfA in A. flavus. Our results revealed that forced overexpression of mtfA results in a drastic decrease or elimination of several secondary metabolites, among them AFB1. The reduction in AFB1 was accompanied by a decrease in aflR expression. Furthermore, mtfA also regulated development; conidiation was influenced differently by this gene depending on the type of colonized substrate. In addition to its effect on conidiation, mtfA is necessary for normal maturation of sclerotia. Importantly, mtfA affects pathogenicity of A. flavus when colonizing peanut seeds. Aflatoxin production in colonized seeds was decreased in the deletion mtfA strain and particularly in the overexpression strain, where only trace amounts were detected. Interestingly, a more rapid colonization of the seed tissue occurred when mtfA was overexpressed, coinciding with an increase in lipase activity and faster maceration of the oil seed.