ARS | Publication request: NsdC and NsdD affect Aspergillus flavus morphogenesis and aflatoxin production

Submitted to: Eukaryotic Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2012
Publication Date: September 15, 2012
Citation: Cary, J.W., Harris Coward, P.Y., Ehrlich, K., Mack, B.M., Kale, S.P., Larey, C., Calvo, A.M. 2012. NsdC and NsdD affect Aspergillus flavus morphogenesis and aflatoxin production. Eukaryotic Cell. 11(9):1104-1111.

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 two genes, designated nsdC and nsdD, 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 the nsd genes control the development of the structure that harbors the fungal spores termed the conidiophore. We can now use what we have learned from these studies to try and identify other A. flavus genes that are part of the nsdC and nsdD control circuit and use this knowledge to aid in unraveling the mechanisms responsible for production of aflatoxin and sclerotia. This in turn will help in devising strategies for eliminating fungal toxin contamination of food and feed crops.

Technical Abstract: The transcription factors NsdC and NsdD have been shown to be necessary for sexual development in Aspergillus nidulans. Herein we examine the role of these proteins in development and aflatoxin production of the agriculturally important, aflatoxin-producing fungus, Aspergillus flavus. We found that both NsdC and NsdD are required for production of asexual sclerotia and for normal aflatoxin biosynthesis. Significant differences in conidiophore morphology were observed in nsdC and nsdD deletion mutants, including shortened stipes and altered structure of the conidial heads compared to the wild-type A. flavus. In addition, 'nsdC and 'nsdD mutants produced a dark pigment during growth on agar medium that was not observed in the wild-type. Protein-protein interaction experiments showed that both NsdC and NsdD are able to bind the global regulator of secondary metabolism and development, LaeA. However only NsdC but not NsdD, was observed to bind to another global regulator of secondary metabolism and development, VeA. Our results suggest that NsdC and NsdD regulate transcription of genes required for early processes in conidiophore development that are different than those required for spore formation.