|Georgianna, D. Ryan|
|Bok, Jin Woo|
Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2009
Publication Date: 1/15/2010
Citation: Georgianna, D., Fedorova, N.D., Burroughs, J.L., Dolezal, A.L., Bok, J., Horowitz-Brown, S., Woloshuk, C.P., Yu, J., Keller, N.P., Payne, G.A. 2010. Beyond aflatoxin: four distinct expression patterns and functional roles associated with Aspergillus flavus secondary metabolism gene clusters. Molecular Plant Pathology. 11(2):213-226. Interpretive Summary: Aflatoxins are toxic and cancer-inducing compounds produced by the fungal mold Aspergillus flavus and A. parasiticus. Contamination of agricultural commodities by aflatoxins poses serious health hazard to animals and human beings. Due to health and food safety concerns, the mechanism of aflatoxin formation and prevention of aflatoxin contamination have been investigated in great detail. Aspergillus flavus genomics and functional genomics including microarray technologies, provides a rapid and effective method for identification of the genes involved in aflatoxin formation and promises effective control strategy being developed through biotechnology. The Aspergillus flavus functional genomics studies will help scientists in investigating the mechanism of aflatoxin formation for devising strategies to control aflatoxin contamination.
Technical Abstract: Species of Aspergillus produce a diverse array of secondary metabolites, and recent genomic analysis has predicted that these species have the capacity to synthesize many more compounds. It has been possible to infer the presence of 55 gene clusters associated with secondary metabolism in Aspergillus flavus; however, only three metabolic pathways—aflatoxin, cyclopiazonic acid (CPA) and aflatrem—have been assigned to these clusters. To gain an insight into the regulation of and to infer the ecological significance of the 55 secondary metabolite gene clusters predicted in A. flavus, we examined their expression over 28 diverse conditions. Variables included culture medium and temperature, fungal development, colonization of developing maize seeds and misexpression of laeA, a global regulator of secondary metabolism. Hierarchical clustering analysis of expression profiles allowed us to categorize the gene clusters into four distinct clades. Gene clusters for the production of aflatoxins, CPA and seven other unknown compound(s) were identified as belonging to one clade. To further explore the relationships found by gene expression analysis, aflatoxin and CPA production were quantified under five different cell culture environments known to be conducive or nonconducive for aflatoxin biosynthesis and during the colonization of developing maize seeds. Results from these studies showed that secondary metabolism gene clusters have distinctive gene expression profiles. Aflatoxin and CPA were found to have unique regulation, but are sufficiently similar that they would be expected to co-occur in substrates colonized with A. flavus.