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Title: RmtA, a putative arginine methyltransferase, regulates secondary metabolism and development in Aspergillus flavus

item SATTERLEE, TIMOTHY - Northern Illinois University
item Cary, Jeffrey
item CALVO, ANA - Northern Illinois University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2016
Publication Date: 5/23/2016
Citation: Satterlee, T., Cary, J.W., Calvo, A.M. 2016. RmtA, a putative arginine methyltransferase, regulates secondary metabolism and development in Aspergillus flavus. PLoS One. 11(5):e0155575. doi:10.1371/journal.pone.0155575.

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 rmtA, from A. flavus that when inactivated significantly increases the numbers of conidia formed while reducing the ability of the fungus to produce structures known as sclerotia that help the fungus to spread and survive in the field under adverse conditions. In addition, this study showed that rmtA controls the production aflatoxins as well as other secondary metabolites produced by A. flavus. Identification of rmtA will add to our knowledge of regulation of growth and toxin production in A. flavus and this in turn will help in devising strategies for eliminating fungal toxin contamination of food and feed crops.

Technical Abstract: Aspergillus flavus is found colonizing numerous oil seed crops such as corn, peanuts, sorghum, treenuts and cotton worldwide, contaminating them with aflatoxin and other harmful potent toxins. In the phylogenetically related model fungus Aspergillus nidulans, the methyltransferase, RmtA, has been described to be involved in epigenetics regulation through histone modification. Epigenetics regulation affects a variety of cellular processes, including morphogenesis and secondary metabolism. Our study shows that deletion of rmtA in A. flavus results in hyperconidiating colonies, indicating that rmtA is a repressor of asexual development in this fungus. The increase in conidiation in the absence of rmtA coincides with greater expression of brlA, abaA, and wetA compared to that in the wild type. Additionally, the rmtA deletion mutant presents a drastic reduction or loss of sclerotial production, while forced expression of this gene increased the ability of this fungus to generate these resistant structures, revealing rmtA as a positive regulator of sclerotial formation. Importantly, rmtA is also required for the production of aflatoxin B1 in A. flavus, affecting the expression of aflJ. Furthermore, biosynthesis of additional metabolites is also controlled by rmtA, indicating a broad regulatory output in the regulation of secondary metabolism. This study also revealed that rmtA positively regulates the expression of the global regulatory gene veA, which could contribute to mediate the effects of rmtA on development and secondary metabolism in this relevant opportunistic plant pathogen.