title: A maize cystatin suppresses host immunity by inhibiting apoplastic cysteine proteases.
abstract: Ustilago maydis is a biotrophic pathogen causing maize (Zea mays) smut disease. Transcriptome profiling of infected maize plants indicated that a gene encoding a putative cystatin (CC9) is induced upon penetration by U. maydis wild type. By contrast, cc9 is not induced after infection with the U. maydis effector mutant Δpep1, which elicits massive plant defenses. Silencing of cc9 resulted in a strongly induced maize defense gene expression and a hypersensitive response to U. maydis wild-type infection. Consequently, fungal colonization was strongly reduced in cc9-silenced plants, while recombinant CC9 prevented salicylic acid (SA)-induced defenses. Protease activity profiling revealed a strong induction of maize Cys proteases in SA-treated leaves, which could be inhibited by addition of CC9. Transgenic maize plants overexpressing cc9-mCherry showed an apoplastic localization of CC9. The transgenic plants showed a block in Cys protease activity and SA-dependent gene expression. Moreover, activated apoplastic Cys proteases induced SA-associated defense gene expression in naïve plants, which could be suppressed by CC9. We show that apoplastic Cys proteases play a pivotal role in maize defense signaling. Moreover, we identified cystatin CC9 as a novel compatibility factor that suppresses Cys protease activity to allow biotrophic interaction of maize with the fungal pathogen U. maydis.
authors.affiliation: Max Planck Institute for Terrestrial Microbiology, D-35043 Marburg, Germany.
authors.forename: Karina
authors.initials: K
authors.lastname: van der Linde
authors.forename: Christoph
authors.initials: C
authors.lastname: Hemetsberger
authors.forename: Christine
authors.initials: C
authors.lastname: Kastner
authors.forename: Farnusch
authors.initials: F
authors.lastname: Kaschani
authors.forename: Renier A L
authors.initials: RA
authors.lastname: van der Hoorn
authors.forename: Jochen
authors.initials: J
authors.lastname: Kumlehn
authors.forename: Gunther
authors.initials: G
authors.lastname: Doehlemann
mesh_terms: D015891:Cystatins / Q000378:metabolism*; D057056:Cysteine Proteases / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D054884:Host-Pathogen Interactions; D008969:Molecular Sequence Data; D057865:Plant Immunity; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D020156:Salicylic Acid / Q000378:metabolism; D014588:Ustilago / Q000472:pathogenicity*; D003313:Zea mays / Q000235:genetics / Q000276:immunology* / Q000382:microbiology
chemical_list: D015891:Cystatins; D010940:Plant Proteins; D057056:Cysteine Proteases; D020156:Salicylic Acid