Dothideomycete–Plant Interactions Illuminated by Genome Sequencing and EST Analysis of the Wheat Pathogen Stagonospora nodorum

Abstract

Stagonospora nodorum is a major necrotrophic fungal pathogen of wheat (Triticum aestivum) and a member of the Dothideomycetes, a large fungal taxon that includes many important plant pathogens affecting all major crop plant families. Here, we report the acquisition and initial analysis of a draft genome sequence for this fungus. The assembly comprises 37,164,227 bp of nuclear DNA contained in 107 scaffolds. The circular mitochondrial genome comprises 49,761 bp encoding 46 genes, including four that are intron encoded. The nuclear genome assembly contains 26 classes of repetitive DNA, comprising 4.5% of the genome. Some of the repeats show evidence of repeat-induced point mutations consistent with a frequent sexual cycle. ESTs and gene prediction models support a minimum of 10,762 nuclear genes. Extensive orthology was found between the polyketide synthase family in S. nodorum and Cochliobolus heterostrophus, suggesting an ancient origin and conserved functions for these genes. A striking feature of the gene catalog was the large number of genes predicted to encode secreted proteins; the majority has no meaningful similarity to any other known genes. It is likely that genes for host-specific toxins, in addition to ToxA, will be found among this group. ESTs obtained from axenic mycelium grown on oleate (chosen to mimic early infection) and late-stage lesions sporulating on wheat leaves were obtained. Statistical analysis shows that transcripts encoding proteins involved in protein synthesis and in the production of extracellular proteases, cellulases, and xylanases predominate in the infection library. This suggests that the fungus is dependant on the degradation of wheat macromolecular constituents to provide the carbon skeletons and energy for the synthesis of proteins and other components destined for the developing pycnidiospores.

Identification and evolution of fungal mitochondrial tyrosyl-tRNA synthetases with group I intron splicing activity

“…S7). A possible explanation is suggested by recent studies, which showed that S. nodorum differs from other Pezizomycotina in lacking a group I intron in its mtLSU gene (19). S. nodorum retains at least one other mt group I intron, but Mycosphaerella graminicola, a fungus belonging to the same class (Dothideomycetes), completely lacks mt group I introns (19).…”

A Zinc-Finger-Family Transcription Factor, AbVf19, Is Required for the Induction of a Gene Subset Important for Virulence in Alternaria brassicicola

“…The importance of enzymes in depolymerizing host plant materials in late-stage pathogenesis was proposed previously (Solomon et al, 2003). Some hydrolytic enzymes are dominantly expressed during late-stage infection in other phytopathogenic fungi (Dean et al, 2005;Hane et al, 2007).…”

Plant breeding for disease resistance in the age of effectors

“…Pathogen genome sequencing, which is now a normal rather than an extraordinary budget item, is the primary data that reveals pathogen effector molecules. In our work, sequencing the S. nodorum genome revealed the presence of ToxA Hane et al 2007;Liu et al 2006). This is one of at least a dozen host-specific toxins that operate in the wheat S. nodorum pathosystem (Friesen et al 2008b).…”