The Secondary Metabolite Toxin, Sirodesmin PL, and Its Role in Virulence of the Blackleg Fungus
Sirodesmin PL is a secondary metabolite toxin produced by Leptosphaeria maculans, a fungus that causes blackleg disease of oilseed rape (Brassica napus). Biosynthesis of this epipolythiodioxopiperazine (ETP) toxin involves a cluster of 18 co-regulated genes. Putative ETP gene clusters have been found in 14 taxa discontinuously distributed amongst ascomycetes. Movement of entire clusters by horizontal gene transfer is the most parsimonious hypothesis to explain this discontinuous distribution. A mutant of L. maculans that does not produce sirodesmin PL forms similar sized lesions on cotyledons of B. napus to those formed by the wild type. However, it is half as effective in colonising stems, as indicated by reduced lesion size and reduced fungal biomass. This implicates sirodesmin PL as a virulence factor in B. napus stems. Expression patterns of two of the cluster genes is consistent with the distribution of sirodesmin PL in planta, as revealed by mass spectrometry experiments. The sirodesmin-deficient mutant has less antibacterial and antifungal activity than the wild type, suggesting that sirodesmin PL may play a role in protecting L.maculans against competition from other micro-organisms.
KeywordsHorizontal gene transfer mycotoxin secondary metabolite sirodesmin
We thank the Australian Research Council and the Grains Research and Development Corporation for funding our research.
- Cramer RA, Gamcsik MP, Brooking RM, Najvar LK, Krikpatrick WR, Patterson TF, Balibar CJ, Graybill JR, Perfect JR, Abraham SN, Steinbach WJ (2006) Disruption of a nonribosomal peptide synthetase in Aspergillus fumigatus eliminates gliotoxin production. Eukaryot Cell 5:979–980Google Scholar
- Ferezou JP, Quesneau-Thierry A, Barbier M, Kollmann A, Bousquet JF (1980a) Structure and synthesis of phomamide, a new piperazine-2,5-dione related to the sirodesmins, isolated from the culture medium of Phoma lingam Tode. J Chem Soc, Perkin Trans 1: Org Bio-Org Chem (1972–1999), 113–115Google Scholar
- Fox EM, Howlett BJ (2008b) Secondary metabolism: regulation and role in fungal biology. Curr Opin Microbiol 11:481–487Google Scholar
- 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 Genet Biol 45:671–682Google Scholar
- Kupfahl C, Heinekamp T, Geginat G, Ruppert T, Hartl A, Herbert H, Brakhage AA (2006) Deletion of the gliP gene of Aspergillus fumigatus results in loss of gliotoxin production but has no effect on virulence of the fungus in a low-dose mouse infection model. Mol Microbiol 62:292–302PubMedCrossRefGoogle Scholar