Genes responsible for the biosynthesis of secondary metabolites are typically clustered in filamentous fungi. The origin and evolutionary pressures that maintain such clusters are largely unknown. We have cloned a gene cluster encoding enzymes in the biosynthesis of a toxin, sirodesmin, from Leptosphaeria maculans, which causes blackleg disease of canola. Sirodesmin belongs to the epipolythiodioxopiperazine (ETP) class of toxins, which is only produced by fungi and confers toxicity via reduction of a disulfide bond. We are using comparative genomics to determine biosynthetic pathways for ETPs. Putative ETP gene clusters are present in three fungi for which complete genome sequences are available. These are the opportunistic human pathogen Aspergillus fumigatus, the rice blast fungus, Magnaporthe grisea and the wheat head scab fungus, Fusarium graminaerum. A. fumigatus makes the ETP gliotoxin, which causes apoptotic and necrotic cell death, as do the distantly related fungi, Penicillium bilaii and Trichoderma virens. We are attempting to characterise the gliotoxin biosynthetic gene clusters in these fungi. Analysis of the arrangement and sequences of genes in these three clusters may uncover clues about how the clusters evolved.
Full conference title:
23rd Fungal Genetics Conference
- Fungal Genetics Conference 23rd (2002)