2010 Annual Report
For examining all the genes and the genetic mechinery involved in the production of the harmful (carcinogenic) compound aflatoxin by the fungus Aspergillus (A.)flavus on crops, the entire fungal deoxyribonucleic acid (DNA) was determined through whole genome sequencing at J. Craig Venter Institute (JCVI) in collaboration with North Carolina State University. Primary analysis of the DNA indicated that the Aspergillus flavus genome size is about 36.8 Mega Base pairs. Comparing the whole genome between the fungus Aspergillus flavus and Aspergillus oryzae (a non-toxigenic food grade industrial organism) demonstrated that the genome size, genome structure, gene categories, and gene homology are quite similar. However, each species contains a unique set of about 300 genes. The ones in A. flavus may contribute to aflatoxin production.
Using glass slides contaning all the genes of the fungus (microarray fabricated at JCVI), genome wide gene profiling experiments have been conducted under specific conditions that favor aflatoxin production in the fungus. Genes and gene clusters that are putatively involved in aflatoxin formation have been identified. Several research papers have been published and a few manuscripts are under preparation.
In parallel with microarray gene profiling experiments, we are currently shifting to Next Generation Sequencing technologies to identify genes potentially involved in the formation and regulation of aflatoxin production. Preliminary results by the technique ribonucleic acid (RNA)-Seq (Illumina) revealed the mechanism of aflatoxin production under specific temperature regimen. Under high temperature, the expression of specific regulatory genes, aflR and aflS, is significantly reduced. The change in ratio of aflR to aflS in high temperature is the main reason for shutting off aflatoxin production.
The DNA sequence data obtained A. flavus expressed sequence tags (EST) and whole genome sequence have been submitted to National Center for Biotechnology Information (NCBI) GenBank (genetic sequence) database. The microarray data are also submitted to the NCBI Gene Expression Omnibus (GEO) database. A database web server containing Aspergillus flavus EST and whole genome databases has been established at the Mid South Area Genomics Center for free access by United States Department of Agriculture/Agricultural Research Service scientists. Progress by cooperators was monitored through routine teleconferencing, meetings, and scientific presentations of recent findings to the project.