Mutations to LmIFRD affect cell wall integrity, development and pathogenicity of the ascomycete Leptosphaeria maculans

Maintaining cell wall integrity is essential for fungal growth and development. We describe two mutants with altered expression of a gene, LmIFRD, from the ascomycete Leptosphaeria maculans. Truncation of the LmIFRD transcript in a T-DNA insertional mutant led to slower germination, less sporulation and loss-of-pathogenicity towards Brassica napus, whereas silencing of the LmIFRD transcript led to increased germination, sporulation and earlier infection. The increased tolerance to cell wall lysing enzymes and cell wall-disrupting compounds of the T-DNA mutant contrasts with decreased tolerance of the silenced mutant and suggests altered cell wall integrity and accessibility to 1,3-linked glucan and chitin. Lectin binding experiments and monosaccharide analysis revealed altered polysaccharide content and structure within the cell wall of the LmIFRD mutants, notably increased 1,3-linked galactose and chitin within the cell wall of the T-DNA mutant. This is the first analysis of monosaccharide linkage composition of cell walls of spores and mycelia for any dothideomycete.