Gene Networks Controlling Development, Pathogenicity and Secondary Metabolism in Aspergillus

Non-Technical Summary: Aspergillus flavus contaminates developing seeds of corn, peanuts, cotton and tree nuts and many other crop plants with the potent carcinogen aflatoxin. The content of aflatoxin in food is regulated at 20 parts per billion in the US and at even lower levels internationally. Thus aflatoxin contamination often presents a barrier to international trade. The most economically sound control practice is to develop resistant plants. Unfortunately, sources of resistance to aflatoxin contamination have been difficult to identify due to our lack of understanding about this organism. The goal of this project is to better understand the factors governing development, aflatoxin production and pathogenicity of A. flavus in order that more effective control procedures can be developed. Our approach to achieve this goal is to first design arrays representing all of the genes in this fungus. Next, these arrays will be used to determine when the genes are on during different growth conditions. These studies will allow us to identified key genes involved in the biosynthesis and regulation of aflatoxin and those required for pathogenicity. These genes can then be targeted for disruption to block the growth and aflatoxin production by the fungus. <P> Approach: We will work closely with Affymetrix Corporation to develop a commercially available comprehensive Aspergillus flavus expression array. Affymetrix will utilize the A. flavus genomic sequence and available EST sequences to design a custom A. flavus GeneChip expression array. In addition to the standard controls we will include intergenic DNA from A. flavus and for corn, as we will be assaying RNA isolated from infected corn. Affymetrix will distribute the A. flavus chips as made-to-order products. This arrangement will allow A. flavus and aflatoxin researchers worldwide to purchase A. flavus chips. These arrays will be used in laboratory studies to compare gene expression patterns between wild type and mutant strains. Key genes identified for morphological development or secondary metabolism will be disrupted and the phenotype evaluated. These arrays will also be used in field and laboratory studies to identify pathogenicity factors in A. flavus and to determine the effect of corn seed composition on aflatoxin biosynthesis.