title: Endoplasmic reticulum glucosidases and protein quality control factors cooperate to establish biotrophy in Ustilago maydis.
abstract: Secreted fungal effectors mediate plant-fungus pathogenic interactions. These proteins are typically N-glycosylated, a common posttranslational modification affecting their location and function. N-glycosylation consists of the addition, and subsequent maturation, of an oligosaccharide core in the endoplasmic reticulum (ER) and Golgi apparatus. In this article, we show that two enzymes catalyzing specific stages of this pathway in maize smut (Ustilago maydis), glucosidase I (Gls1) and glucosidase II β-subunit (Gas2), are essential for its pathogenic interaction with maize (Zea mays). Gls1 is required for the initial stages of infection following appressorium penetration, and Gas2 is required for efficient fungal spreading inside infected tissues. While U. maydis Δgls1 cells induce strong plant defense responses, Δgas2 hyphae are able to repress them, showing that slight differences in the N-glycoprotein processing can determine the extent of plant-fungus interactions. Interestingly, the calnexin protein, a central element of the ER quality control system for N-glycoproteins in eukaryotic cells, is essential for avoiding plant defense responses in cells with defective N-glycoproteins processing. Thus, N-glycoprotein maturation and this conserved checkpoint appear to play an important role in the establishment of an initial biotrophic state with the plant, which allows subsequent colonization.
authors.affiliation: Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide-Consejo Superior de Investigaciones Científicas, 41013 Seville, Spain.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Fernández-Álvarez
authors.forename: Alberto
authors.initials: A
authors.lastname: Elías-Villalobos
authors.forename: Alberto
authors.initials: A
authors.lastname: Jiménez-Martín
authors.forename: Miriam
authors.initials: M
authors.lastname: Marín-Menguiano
authors.forename: José I
authors.initials: JI
authors.lastname: Ibeas
mesh_terms: D037281:Calnexin / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005959:Glucosidases / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D054884:Host-Pathogen Interactions; D009154:Mutation; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D014588:Ustilago / Q000201:enzymology / Q000378:metabolism* / Q000472:pathogenicity*; D003313:Zea mays / Q000382:microbiology* / Q000502:physiology
chemical_list: D005656:Fungal Proteins; D006023:Glycoproteins; D037281:Calnexin; D005959:Glucosidases