Aflatoxin-like gene clusters and how they evolved

Abstract

Almost all filamentous fungi produce one or more polyketide -derived secondary metabolites (Demain and Fang 2000). The most common secondary metabolite is 1,4-dihydroxynaphthoquinone, the precursor of melanin. Others are precursors of fungal pigment s or are toxic to plants, animals, or soil microorganisms. Their toxicity often is used defensively by the fungus against competing organisms, or offensively, by facilitating invasion of plants. The best studied of the polyketide s are the bis-furans known collectively as aflatoxin s (AF). In this chapter, we will discuss current knowledge concerning the AF gene cluster and how such clusters evolved. Two types of gene cluster s are found in known isolates of AF-producing fungi. These differ mainly in the order of the genes (Fig. 5.1). AF-producing species such as A. flavus and A. parasiticus have the gene cluster shown in Fig. 5.1a, while the newly discovered Aspergillus species, ochraceoroseus, astellata and venezuelensis, have a gene cluster similar to that of the ST-producing species A. nidulans (Fig. 5.1b) (Cary and Ehrlich 2006). Two genes in the cluster (aflR and aflJ) encode proteins involved in transcriptional activation of most of the other structural genes (Chang 2003, 2004). © 2010 Springer-Verlag Berlin Heidelberg.