Pathogenicity of Stagonospora nodorum requires malate synthase

Abstract

SummaryA gene encoding malate synthase, a key enzyme of the glyoxylate cycle, has been cloned and characterized in the necrotrophic wheat pathogen Stagonospora nodorum . Expression studies of Mls1 showed high levels of transcript in ungerminated spores whereas malate synthase enzyme activities were low. Expression studies in planta found that Mls1 transcript levels decreased ª ª ª ª 10-fold upon germination before slowly increasing throughout the remainder of the infection. To characterize Mls1 further, the gene was disrupted in S. nodorum by homologous recombination. In the absence of any supplied carbon source, the mls1 spores were unable to germinate and consequently the mutants were non-pathogenic. Germination and pathogenicity could be restored by the addition of either glucose or sucrose, implying that S. nodorum is reliant upon the catabolism of lipids for infection. Furthermore, analysis of lipid bodies in the mutant strain indicated that lipid mobilization and, consequently, peroxisomal b b b b -oxidation of fatty acids is delayed or inhibited by the disruption of the glyoxylate cycle. This study has demonstrated for the first time in a fungal phytopathogen the requirement of malate synthase for pathogenicity, suggesting that gluconeogenesis is both dependent on the glyoxylate cycle and required for infection.

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

“…nodorum is an experimentally tractable organism, which is easily handled in defined media, was one of the first fungal pathogens to be genetically manipulated (Cooley et al, 1988), and has been a model for fungicide development (Dancer et al, 1999). Molecular analysis of pathogenicity determinants is aided by facile tools for gene ablation and rapid in vitro phenotypic screens, and thus far, a small number of genes required for pathogenicity have been identified (Cooley et al, 1988;Bailey et al, 1996;Bindschedler et al, 2003;Solomon et al, 2003bSolomon et al, , 2004aSolomon et al, , 2004bSolomon et al, , 2005Solomon et al, , 2006a. It has thus emerged as a model for dothideomycete pathology.…”

“…The hyphae rapidly colonize the leaves and begin to produce pycnidia in 7 to 10 d. The infection has been divided into three metabolic phases (Solomon et al, 2003a). The first phase is penetration of the host epidermis and is fuelled predominantly by lipid stores in the spores (Solomon et al, 2004a); the second is proliferation throughout the interior of the leaf, involves toxin release , and uses hostderived simple carbohydrate sources (Solomon et al, 2004a); the final phase produces the new spores, but so far the metabolic requirements for pycnidiation are unclear.…”

Parallels in Fungal Pathogenesis on Plant and Animal Hosts

“…The glyoxylate cycle plays an important role in the nutrition of both plant-and animal-pathogenic fungi. These include plant pathogens Magnaporthe grisea (88), Leptosphaeria maculans (42), and Stagonospora nodorum (76) and animal pathogens such as C. albicans (51) and Aspergillus fumigatus (27). Fungal mutants with mutations in the glyoxylate cycle enzymes isocitrate lyase or malate synthase have low levels of germination and are not infectious.…”

Metabolite profiling identifies the mycotoxin alternariol in the pathogen Stagonospora nodorum

“…is a major pathogen of wheat and other cereals (Solomon et al, 2006d) causing stagonospora nodorum blotch (previously septoria nodorum blotch and glume blotch). Previous studies focused on understanding the disease have demonstrated critical roles for host-specific toxins and various primary metabolic pathways for effective fungal pathogenicity (Solomon et al, 2004a;Solomon et al, 2005a;Solomon et al, 2006a;Solomon et al, 2006e).…”