AFLATOXIN CONTROL THROUGH TARGETING MECHANISMS GOVERNING AFLATOXIN BIOSYNTHESIS IN CORN AND COTTONSEED
Location: Food and Feed Safety Research
Title: EST Profiling for Elucidation of Molecular Regulation of Aflatoxin bBiosynthesis in Aspergillus flavus
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 2006
Publication Date: September 26, 2006
Citation: Yu, J., Wilkinson, J.R., Cleveland, T.E., Campbell, B.C., Bhatnagar, D., Payne, G.A., Nierman, W.C. 2006. EST profiling for elucidation of molecular regulation of aflatoxin biosynthesis in Aspergillus flavus. In: Proceedings of the Myco-Globe Conference: Advances on Genomics, Biodiversity and Rapid Systems for Detection of Toxigenic Fungi and Mycotoxins, September 26-30, 2006, Bari, Italy. p. 29.
Aflatoxins are toxic and carcinogenic polyketide metabolites produced by fungal species, including Aspergillus flavus and A. parasiticus. Many internal and external factors, such as nutrition and environment, affect aflatoxin biosynthesis. A. flavus EST has been carried out and a microarray has been constructed at The Institute for Genomic Research (TIGR) for profiling gene expression and for identifying potential regulatory networks controlling aflatoxin contamination in food and feeds. The gene expression profiles in aflatoxin-supportive medium, Yeast Extract Sucrose (YES), vs. non-aflatoxin-supportive medium, Yeast Extract (YE), were evaluated in A. parasiticus. When cultures were shifted from YE to YES media, the aflatoxin levels were reduced initially from 3 to 12-hour post-shift. But, aflatoxin levels in YES were about 10-fold higher than in YE after 24-hour post shift. Microarray analysis comparing gene expression profiles from the 48-hour YE cultures with those from YES cultures identified a total of 2,120 genes that were expressed across all experiments, including most of the aflatoxin biosynthesis genes. By one-way analysis of variance (ANOVA), 56 genes were identified to be significantly expressed across all time points. Amino acids affect aflatoxin biosynthesis in different ways depending on the type of amino acids. When the YES medium was supplemented with 50 mM tryptophan (Trp) in A. flavus, biosynthesis of aflatoxin B1 and B2 was found to be significantly reduced. In contrast, aflatoxin B1 and G1 biosynthesis was significantly increased in A. parasiticus. Microarray analysis revealed 77 genes either significantly up or down regulated, including the aflatoxin biosynthetic genes aflD (nor-1), aflE (norA), and aflO (omtB). It is clear that the regulatory mechanisms of aflatoxin biosynthesis in response to Trp in A. flavus and A. parasiticus are different. Further investigation of these candidate genes may help to identify a regulatory gene(s) or factor(s) of aflatoxin biosynthesis.