Pep1, a secreted effector protein of Ustilago maydis, is required for successful invasion of plant cells

• Published in: PLoS pathogens Vol. 5; no. 2; p. e1000290
• Main Authors: Doehlemann, Gunther, van der Linde, Karina, Assmann, Daniela, Schwammbach, Daniela, Hof, Alexander, Mohanty, Amitabh, Jackson, David, Kahmann, Regine
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.02.2009; Public Library of Science (PLoS)
• Subjects: Arrests; Bacterial proteins; Basidiomycota; Flowers & plants; Fungal Proteins - chemistry; Fungal Proteins - genetics; Fungal Proteins - metabolism; Fungi; Gene Expression Regulation, Plant; Genetics and Genomics/Gene Expression; Hordeum - microbiology; Host-Pathogen Interactions; Hyphae - growth & development; Infections; Microbiology; Microbiology/Plant-Biotic Interactions; Molecular weight; Mutation; Oligonucleotide Array Sequence Analysis; Physiological aspects; Plant Biology/Plant-Biotic Interactions; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Proteins - genetics; Plant Proteins - immunology; Plant Proteins - metabolism; Plant-pathogen relationships; Plasma; Plastids - pathology; Protein folding; Tumors; Ustilago - genetics; Ustilago - growth & development; Ustilago - metabolism; Ustilago - pathogenicity; Zea mays - genetics; Zea mays - immunology; Zea mays - microbiology; United States
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1000290

The basidiomycete Ustilago maydis causes smut disease in maize. Colonization of the host plant is initiated by direct penetration of cuticle and cell wall of maize epidermis cells. The invading hyphae are surrounded by the plant plasma membrane and proliferate within the plant tissue. We identified a novel secreted protein, termed Pep1, that is essential for penetration. Disruption mutants of pep1 are not affected in saprophytic growth and develop normal infection structures. However, Deltapep1 mutants arrest during penetration of the epidermal cell and elicit a strong plant defense response. Using Affymetrix maize arrays, we identified 116 plant genes which are differentially regulated in Deltapep1 compared to wild type infections. Most of these genes are related to plant defense. By in vivo immunolocalization, live-cell imaging and plasmolysis approaches, we detected Pep1 in the apoplastic space as well as its accumulation at sites of cell-to-cell passages. Site-directed mutagenesis identified two of the four cysteine residues in Pep1 as essential for function, suggesting that the formation of disulfide bridges is crucial for proper protein folding. The barley covered smut fungus Ustilago hordei contains an ortholog of pep1 which is needed for penetration of barley and which is able to complement the U. maydis Deltapep1 mutant. Based on these results, we conclude that Pep1 has a conserved function essential for establishing compatibility that is not restricted to the U. maydis / maize interaction.