Unlocking the secrets behind secondary metabolism:: A review of Aspergillus flavus from pathogenicity to functional genomics

Aspergillus flavus has received a considerable amount of attention due to its ability to produce aflatoxin, a secondary metabolite that is both immunosuppressive and carcinogenic to animals and humans. Research on aflatoxin over the last 40 years has made it one of the best Studied fungal secondary metabolites. In spite of the large volume of research in this area, many unanswered questions remain concerning the genetic regulation of aflatoxin production and the molecular signals that intimately associate the synthesis of aflatoxin with specific environmental and nutritional conditions. It is anticipated that the tools now available in the field of genomics will build upon our existing knowledge and provide answers to some of these questions. Complete genome sequences are now available for a number of fungal species that are closely related to A. flavus. This information can be used along with current genomic analyses in A. flavus to more closely examine the biosynthesis and regulation of secondary metabolism. The intent of this review is to summarize the large body of knowledge that exists from many years of research on A. flavus, with the hope that this information in the light of new genomic studies may bring scientists closer to unraveling the web of regulatory circuits that govern aflatoxin biosynthesis. Specifically, scientific findings in the following areas will be presented: classification and phylogenetic analyses of A. flavus, population biology, ecology and pathogenicity in agricultural environments, classical genetics including linkage group and mutant analyses, gene clusters, regulation of aflatoxin biosynthesis, and genomics.