Gene Clusters for Fungal Toxin Biosynthesis

Filamentous fungi produce a range of secondary metabolites and usually genes for biosynthesis of these molecules are clustered. Epipolythiodioxopiperazines (ETPs) are toxic secondary metabolites made by a diverse range of unrelated ascomycetous fungi. The toxicity of ETPs is conferred by the presence of a disulphide bridge, which inactivates proteins via reaction with thiol groups, and generates reactive oxygen species by redox cycling. The blackleg fungus, Leptosphaeria maculans secretes sirodesmin PL. Gliotoxin, which is associated with invasive aspergillosis of immunocompromised patients is the best-known ETP.

We have cloned the gene clusters for biosynthesis of sirodesmin and gliotoxin. This was the first report of ETP biosynthetic genes in any fungus.

We have characterized a transcription factor sirZ in the sirodesmin biosynthetic gene cluster.  This gene has been silenced using RNA interference. Using quantitative RT-PCR we have shown that the resultant mutant has decreased expression of several genes in the pathway genes in the cluster, compared to the wild type strain. Using a high throughput assay based on the toxicity of sirodesmin to Bacillus subtilis, we have isolated L. maculans mutants that are sirodesmin-deficient. We are characterizing the mutated genes in each isolate.

Selected publications

Fox EM, Howlett BJ (2008) Secondary metabolism: regulation and role in fungal biology. Current Opinion in Microbiology manuscript accepted

Howlett BJ (2008) Biosynthesis of epipolythiodioxopiperazine toxins in fungi. Chemistry in Australia 75: 4-7

Fox EM, Gardiner DM, Keller NP, Howlett BJ (2008) A Zn(II)₂Cys₆ DNA binding protein regulates the sirodesmin PL biosynthetic gene cluster in Leptosphaeria maculans. Fungal Genetics and Biology 45: 671-82

Fox EM, Howlett BJ (2008) Biosynthetic gene clusters for epipolythiodioxopiperazines in filamentous fungi. Mycological Research 112: 162-9

Patron NJ, Waller RF, Cozijnsen AJ, Straney DC, Gardiner DM, Nierman WC, Howlett BJ (2007) Origin and distribution of epipolythiodioxopiperazine (ETP) gene clusters in filamentous ascomycetes. BMC Evolutionary Biology 7: 174