Indole-Diterpene Gene Cluster from Aspergillus flavus

Abstract

ABSTRACT Aflatrem is a potent tremorgenic mycotoxin produced by the soil fungus Aspergillus flavus and is a member of a large structurally diverse group of secondary metabolites known as indole-diterpenes. By using degenerate primers for conserved domains of fungal geranylgeranyl diphosphate synthases, we cloned two genes, atmG and ggsA (an apparent pseudogene), from A. flavus . Adjacent to atmG are two other genes, atmC and atmM . These three genes have 64 to 70% amino acid sequence similarity and conserved synteny with a cluster of orthologous genes, paxG , paxC , and paxM , from Penicillium paxilli which are required for indole-diterpene biosynthesis. atmG , atmC , and atmM are coordinately expressed, with transcript levels dramatically increasing at the onset of aflatrem biosynthesis. A genomic copy of atmM can complement a paxM deletion mutant of P. paxilli , demonstrating that atmM is a functional homolog of paxM . Thus, atmG , atmC , and atmM are necessary, but not sufficient, for aflatrem biosynthesis by A. flavus . This provides the first genetic evidence for the biosynthetic pathway of aflatrem in A. flavus .