Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2006
Publication Date: 11/5/2006
Citation: Yu, J., Payne, G.A., Nierman, W.C., Bennett, J.W., Machida, M., Campbell, B.C., Bhatnagar, D., Cleveland, T.E. 2006. Genomics of Aflatoxin Producing Fungi. In: Proceedings of the 10th International Symposium on Toxic Microorganisms (United States - Japan Cooperative Program on Development and Utilization of Natural Resources), November 5-11, 2006, Washington, DC.
Technical Abstract: Aspergillus flavus produces the most potent carcinogens, known as aflatoxins, when it infects agricultural crops. It is also a pathogen that infects plants, animals and human beings. Its close relative, A. oryzae, that shares about 98% identity on DNA level to A. flavus, is neither a pathogen nor produces such toxin. A. oryzae is widely used in food fermentation industry. These Aspergillus species are important to the health of humans and animals and also important to agricultural economy and ecology. The initiation of A. flavus and A. oryzae genomics programs is to solve aflatoxin contamination of agricultural commodity and to improve the quality and efficiency in food fermentation. Tremendous research effort has been undertaken to better understand the mechanism of aflatoxin biosynthesis and its genetic regulation in A. flavus. Identification and elucidation of genes involved in aflatoxin biosynthesis through genomic strategy has been actively pursued. A. flavus Expressed Sequence Tags (EST) is the first phase of our genomics program. A total of 19,618 A. flavus ESTs were generated, from which 7,218 unique EST sequences were assembled. These ESTs have been released to the public in NCBI GenBank database (http://www.ncbi.nlm.nih.gov) and the functional classification has been presented in Gene Index by The Institute for Genomic Research (TIGR, http://www.tigr.org). A. flavus microarray has been constructed at TIGR for gene expression profiling and for identifying potential regulatory networks controlling aflatoxin biosynthesis. Gene profiling using the 5031-element A. flavus amplicon microarray has been performed under different culture media, temperatures and pH conditions. Groups of genes that are potentially involved in aflatoxin production have been identified in response to the conditions. Teamed up with Professor Gary A. Payne, NCSU and Dr. William C. Nierman at TIGR, the A. flavus whole genome sequencing has been completed and the genome sequences have been released to NCBI GenBank database. The A. flavus genome size (36.8 Mb) seems larger than either A. nidulans or A. fumigatus, but similar to its genetic cousin, A. oryzae. The scaffold size ranges from 4.5 Mb to 1 Kb and 99.6% of the predicted genes are contained within the 16 largest scaffolds. Preliminary annotation of the sequence revealed that there are about 12,000 genes in the A. flavus genome. Many genes in the A. flavus genome, which potentially encode for enzymes involved in secondary metabolite production, have been identified. They are putative polyketide synthases (35), putative non-ribosomal peptide synthases (24) and cytochrome P450 enzymes (131). These data can be accessed at http://www.aspergillusflavus.org. The whole genome sequence of A. oryzae has been completed in Japan, which allows the comparison between the two species. The A. flavus whole genome oligo microarray and Affymetrix microarray have been constructed at TIGR and at Affymetrix, respectively. These arrays contain not only all of the A. flavus genes, but A. oryzae unique genes plus additional genes of interest. Comparative genome hybridization studies and genome-wide gene profiling using the newly constructed microarrays are expected to generate significant amounts of data for understanding the mechanism of aflatoxin biosynthesis and thus aid in solving aflatoxin contamination of crops.