Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2004
Publication Date: 5/30/2004
Citation: Kim, J.H., Yu, J., Bhatnagar, D., Cleveland, T.E., Campbell, B.C. 2004. Targeting stress-response genes for control of mycotoxin biosynthesis in Aspergillus [abstract]. 7th European Conference on Fungal Genetics and 1st Aspergillus Workshop, April 17-21, 2004, Copenhagen, Denmark.
Technical Abstract: Certain stress-response genes in aflatoxigenic aspergilli play a significant role for inducing biosynthesis of aflatoxin. For instance, hydrolyzable tannins completely shutdown aflatoxin biosynthesis. The most active constituent of these tannins is gallic acid. By using deletion mutants of Saccharomyces cerevisiae, as a model system, we found the mode of action of gallic acid is as an antioxidant. For example, negative effects on yeasts lacking the antioxidative stress gene ctal exposed to hydrogen peroxide were reversed when the same mutants were treated with gallic acid. Thus, gallic acid counters oxidative stress-response induced biosynthesis of aflatoxin. Examination of a deletion mutant lacking the signal transduction gene sho1, which encodes a transmembrane osmosensor, showed similar results as the cta1 mutant. We identified other stress-response genes upstream from the gene cluster of the aflatoxin biosynthetic pathway. Such stress-response genes are responsible for signal transduction, inducing upregulation of transcription factor(s) further downstream to initiate aflatoxin biosynthesis. To discover genes involved in induction of toxin biosynthesis, we are searching an EST database of A. flavus. Based on results using the model yeast system, described above, we have identified orthologs of yeast MAP kinase-pathway and antioxidative stress-response genes in the A. flavus EST database. In order to study the A. flavus orthologs directly, we are developing a vector system wherein these genes are recombined in yeasts using an artificial chromosome. The system includes a vector having an origin of replication, selectable markers, a yeast centromere, a promoter, and cloning sites for insertion of exogenous cDNA. Our approach complements microarray analysis and allows a high throughput assessment of individual, specifically targeted genes.