eThe global regulatory veA gene governs development and secondary metabolism in numerous fungal species, including Aspergillus flavus. This is especially relevant since A. flavus infects crops of agricultural importance worldwide, contaminating them with potent mycotoxins. The most well-known are aflatoxins, which are cytotoxic and carcinogenic polyketide compounds. The production of aflatoxins and the expression of genes implicated in the production of these mycotoxins are veA dependent. The genes responsible for the synthesis of aflatoxins are clustered, a signature common for genes involved in fungal secondary metabolism. Studies of the A. flavus genome revealed many gene clusters possibly connected to the synthesis of secondary metabolites. Many of these metabolites are still unknown, or the association between a known metabolite and a particular gene cluster has not yet been established. In the present transcriptome study, we show that veA is necessary for the expression of a large number of genes. Twenty-eight out of the predicted 56 secondary metabolite gene clusters include at least one gene that is differentially expressed depending on presence or absence of veA. One of the clusters under the influence of veA is cluster 39. The absence of veA results in a downregulation of the five genes found within this cluster. Interestingly, our results indicate that the cluster is expressed mainly in sclerotia. Chemical analysis of sclerotial extracts revealed that cluster 39 is responsible for the production of aflavarin.A spergillus flavus is a saprophytic filamentous fungus that is also able to colonize economically important crops such as peanuts, cotton, maize, and other oil seed crops during preharvest or storage. Its most efficient mode of dissemination is the production of airborne conidia. In addition, A. flavus produces resistant structures called sclerotia, which allow this fungus to survive adverse environmental conditions for long periods of time (1-3). This opportunistic pathogen produces a wide range of secondary metabolites, including aflatoxins (AFs). Among them, AFB1 is the most mutagenic and carcinogenic natural compound known (4-8). Ingestion of food products contaminated with AFs has been associated with hepatotoxicity, teratogenicity, immunosuppression, and liver cancer (6, 9). AF contamination also results in a negative impact on the economy in developed countries. In the United States alone A. flavus causes more than a billion dollar in losses per year due to contaminated crops (10). In addition to AFs, A. flavus is known to produce other mycotoxins, including cyclopiazonic acid (CPA), a suppressor of the calcium-dependent ATPase in the sarcoplasmic reticulum, and aflatrem, a tremogenic mycotoxin causative of neurological disorders (11,12).Studies of the A. flavus genome have revealed many gene clusters possibly connected to the synthesis of other secondary metabolites. Specifically, 55 different clusters were predicted based on the presence of genes encoding polyketide synthases (PKSs), non...
