The sirodesmin biosynthetic gene cluster of the plant pathogenic fungus Leptosphaeria maculans

Abstract

SummarySirodesmin PL is a phytotoxin produced by the fungus Leptosphaeria maculans, which causes blackleg disease of canola ( Brassica napus ). This phytotoxin belongs to the epipolythiodioxopiperazine (ETP) class of toxins produced by fungi including mammalian and plant pathogens. We report the cloning of a cluster of genes with predicted roles in the biosynthesis of sirodesmin PL and show via gene disruption that one of these genes (encoding a two-module non-ribosomal peptide synthetase) is essential for sirodesmin PL biosynthesis. Of the nine genes in the cluster tested, all are co-regulated with the production of sirodesmin PL in culture. A similar cluster is present in the genome of the opportunistic human pathogen Aspergillus fumigatus and is most likely responsible for the production of gliotoxin, which is also an ETP. Homologues of the genes in the cluster were also identified in expressed sequence tags of the ETP producing fungus Chaetomium globosum . Two other fungi with publicly available genome sequences, Magnaporthe grisea and Fusarium graminearum , had similar gene clusters. A comparative analysis of all four clusters is presented. This is the first report of the genes responsible for the biosynthesis of an ETP.

Population diversity and genomics of the fungal pathogen of canola Leptosphaeria maculans

“…Previous studies have also found reduced expression of this gene leading to the presence of high amounts of "deactyl derivative of sirodesmin PL" (Gardiner et al, 2004). However, the biological importance of this still needs to be deciphered.…”

“…Five genes (Lema_G081880.1-SirH, Lema_G081890.1, Lema_G081900.1-LmUVI-1h, Lema_G081910.1 and Lema_G081920.1-Polyketide synthase) that are part of the 68 kbp sirodesmin biosynthesis cluster (Gardiner et al, 2004), were lost uniquely in D4. All other isolates had conserved genes belonging to this cluster.…”

“…Lema_081920.1 or PKS1 (annotated as polyketide synthase; part of SC_13 cluster) shares 67.5% identity with pksA, the PKS gene involved in aflaxtoxin biosynthesis (Genbank accession AAR32704) (Gardiner et al, 2004;Rouxel et al, 2011). The cluster producing sterigmatocystin in Aspergillus nidulans encodes some genes similar to those in the cluster on SC_13 (Table 4.7; Brown et al (1996)).…”

“…This 68 kbp cluster contains 23 genes, of which 18 are thought to be involved in producing sirodesmin (Genbank accession AY553235). PKS1, which is a part of the putative cluster on SC_13, was characterised as a neighbouring gene but not thought to be involved in synthesis (Gardiner et al, 2004). LmUVI-1h (Lema_G081900.1) and LmHDX1 (Lema_G081930.1) were also thought to not be involved in the process.…”

“…The ultraviolet inducible gene LmUVI-1h is described in Gardiner et al (2004) as a gene present close to the sirodesmin biosynthesis cluster, but not thought to be a part of the cluster (Table 4.7). It shares similarity with the Uvi-1 gene (Genbank accession number BAA96294) of Bipolaris oryzae.…”