Submitted to: International IUPAC Symposium on Mycotoxins and Phycotoxins
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2004
Publication Date: 6/1/2004
Citation: Bhatnagar, D., Yu, J., Ehrlich, K., Cleveland, T.E. Aspergillus genomics: Understanding fungal ecology and aflatoxin production [abstract]. International Union of Pure and Applied Chemistry (IUPAC) Symposium on Mycotoxins and Phycotoxins, May 17-21, 2004, Bethesda, Maryland.
Technical Abstract: Aflatoxins are the most potent natural carcinogens produced primarily by the filamentous fungi, Aspergillus flavus and A. parasiticus. These fungi infect both pre-harvest crops and post-harvest commodities and contaminate them with aflatoxins. Genomics of these aflatoxigenic fungi began with molecular understanding of the biosynthesis of aflatoxins. Studies on the molecular mechanism of aflatoxin B1 biosynthesis have identified 25 genes within a 70 Kb aflatoxin pathway gene cluster, including a gene for the positive transcriptional activator. Genomic studies on A. flavus have been further extended through the A. flavus Expressed Sequenced Tag (EST) project to understand the molecular mechanisms that govern the regulation of aflatoxin biosynthesis, plant-fungal interactions, and evolutionary biology of aflatoxigenic fungi. About 70%-80% of the total genes within the A. flavus genome have been identified (7,214 unique EST sequences) from a normalized cDNA library. Among the 7,214 unique ESTs, 3,728 tentative consensus (TC) sequences have been assembled and 3,486 singleton sequences were identified from 22,324 usable sequences obtained. An A. flavus gene index was constructed on the basis of these identified unique genes. Microarrays containing these unique genes have been constructed. Additionally, the A. flavus EST profile has been compared to the A. oryzae EST data (provided by the Japanese Consortium on the A. oryzae genome project). Using information from EST/microarray experiments for functional genomics studies, vital information for developing new strategies for the control of aflatoxin contamination of crops and for harnessing other biochemical processes of these fungi is expected. Another use of genomics will be to improve the understanding of Aspergillus phylogenetic relationships. Genomic analyses have revolutionized modern understandings of speciation, especially in asexual organisms such as Aspergillus, where geographic separation and environmental adaptations can drive beneficial genetic changes. For Aspergillus, we now know that B and G aflatoxin production is the ancestral trait to B only production, and therefore, that species such as A. parasiticus and A. nomius are ancestral to A. flavus. We have a better understanding through genomics of why important Aspergillus isolates used in soy fermentations and as biocompetitors are atoxigenic. We also have a better understanding of the diversity of isolates that are classified as A. flavus and A. nomius, which leads to increased knowledge of how these organisms are dispersed into new environmental niches. Genomics also holds great promise for better understanding of fundamental processes in Aspergillus, such as heterokaryon incompatibility and sclerotial formation.