Glucosylceramide synthase is essential for alfalfa defensin-mediated growth inhibition but not for pathogenicity of Fusarium graminearum

• Published in: Molecular microbiology Vol. 66; no. 3; pp. 771 - 786
• Main Authors: Ramamoorthy, Vellaisamy, Cahoon, Edgar B, Li, Jia, Thokala, Mercy, Minto, Robert E, Shah, Dilip M
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.11.2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Arabidopsis thaliana; Biological and medical sciences; Cryptococcus neoformans; Defensins - genetics; Defensins - metabolism; Defensins - pharmacology; Enzymes; Flowers & plants; Fundamental and applied biological sciences. Psychology; Fusarium - drug effects; Fusarium - pathogenicity; Fusarium graminearum; Genes; Genetic Complementation Test; Glucosylceramides - metabolism; Glucosyltransferases - genetics; Glucosyltransferases - metabolism; Lycopersicon esculentum; Lycopersicon esculentum - microbiology; Magnetic Resonance Spectroscopy; Medicago; Medicago sativa - metabolism; Microbiology; Miscellaneous; Mutation; Mycology; Pathogens; Triticum - microbiology; Triticum aestivum; Virulence; Zea mays - microbiology; Peptides; Plant pathogen; Fusarium graminearum; Enzyme; Medicago sativa; Synthase; Antimicrobial agent; Fungi; Pathogenicity; Leguminosae; Dicotyledones; Angiospermae; Spermatophyta; Fungi Imperfecti; Fodder crop; Defensin; Thallophyta
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2007.05955.x

Antifungal defensins, MsDef1 and MtDef4, from Medicago spp., inhibit the growth of a fungal pathogen, Fusarium graminearum, at micromolar concentrations. However, molecular mechanisms by which they inhibit the growth of this fungus are not known. We have characterized a functional role of the fungal sphingolipid glucosylceramide in regulating sensitivity of the fungus to MsDef1 and MtDef4. A null mutation of the FgGCS1 gene encoding glucosylceramide synthase results in a mutant lacking glucosylceramide. The ΔFggcs1-null mutant becomes resistant to MsDef1, but not to MtDef4. It shows a significant change in the conidial morphology and displays dramatic polar growth defect, and its mycelia are resistant to cell wall degrading enzymes. Contrary to its essential role in the pathogenicity of a human fungal pathogen, Cryptococcus neoformans, GCS1 is not required for the pathogenicity of F. graminearum. The ΔFggcs1 mutant successfully colonizes wheat heads and corn silk, but its ability to spread in these tissues is significantly reduced as compared with the wild-type PH-1 strain. In contrast, it retains full virulence on tomato fruits and Arabidopsis thaliana floral and foliar tissues. Based on our findings, we conclude that glucosylceramide is essential for MsDef1-mediated growth inhibition of F. graminearum, but its role in fungal pathogenesis is host-dependent.