title: Altered glycosylation of exported proteins, including surface immune receptors, compromises calcium and downstream signaling responses to microbe-associated molecular patterns in Arabidopsis thaliana.
abstract: BACKGROUND
  Calcium, as a second messenger, transduces extracellular signals into cellular reactions. A rise in cytosolic calcium concentration is one of the first plant responses after exposure to microbe-associated molecular patterns (MAMPs). We reported previously the isolation of Arabidopsis thaliana mutants with a "changed calcium elevation" (cce) response to flg22, a 22-amino-acid MAMP derived from bacterial flagellin.
  
  
  RESULTS
  Here, we characterized the cce2 mutant and its weaker allelic mutant, cce3. Besides flg22, the mutants respond with a reduced calcium elevation to several other MAMPs and a plant endogenous peptide that is proteolytically processed from pre-pro-proteins during wounding. Downstream defense-related events such flg22-induced mitogen-activated protein kinase activation, accumulation of reactive oxygen species and growth arrest are also attenuated in cce2/cce3. By genetic mapping, next-generation sequencing and allelism assay, CCE2/CCE3 was identified to be ALG3 (Asparagine-linked glycosylation 3). This encodes the α-1,3-mannosyltransferase responsible for the first step of core oligosaccharide Glc3Man9GlcNAc2 glycan assembly on the endoplasmic reticulum (ER) luminal side. Complementation assays and glycan analysis in yeast alg3 mutant confirmed the reduced enzymatic function of the proteins encoded by the cce2/cce3 alleles - leading to accumulation of M5(ER), the immature five mannose-containing oligosaccharide structure found in the ER. Proper protein glycosylation is required for ER/Golgi processing and trafficking of membrane proteins to the plasma membrane. Endoglycosidase H-insensitivity of flg22 receptor, FLS2, in the cce2/cce3 mutants suggests altered glycan structures in the receptor.
  
  
  CONCLUSIONS
  Proper glycosylation of MAMP receptors (or other exported proteins) is required for optimal responses to MAMPs and is important for immune signaling of host plants.
authors.affiliation: Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany. Fabian.Trempel@ipb-halle.de.
authors.forename: Fabian
authors.initials: F
authors.lastname: Trempel
authors.affiliation: The International Center for Biotechnology, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka, 565, Japan. kajiura@hitzbio.com.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kajiura
authors.affiliation: Current address: Phytopathology, TUM School of Life Sciences, Weihenstephan, Technische Universität München, Emil-Ramann-Str. 2, D-85350, Freising-Weihenstephan, Germany. ranf@wzw.tum.de.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Ranf
authors.affiliation: Current address: Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Weinbergweg 22, D-06120, Halle, Germany. julia.grimmer@biochemtech.uni-halle.de.
authors.forename: Julia
authors.initials: J
authors.lastname: Grimmer
authors.affiliation: Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany. Lore.Westphal@ipb-halle.de.
authors.forename: Lore
authors.initials: L
authors.lastname: Westphal
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, UK. Cyril.Zipfel@sainsbury-laboratory.ac.uk.
authors.forename: Cyril
authors.initials: C
authors.lastname: Zipfel
authors.affiliation: Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany. dscheel@ipb-halle.de.
authors.forename: Dierk
authors.initials: D
authors.lastname: Scheel
authors.affiliation: The International Center for Biotechnology, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka, 565, Japan. fujiyama@icb.osaka-u.ac.jp.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Fujiyama
authors.affiliation: Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany. jlee@ipb-halle.de.
authors.forename: Justin
authors.initials: J
authors.lastname: Lee
mesh_terms: D017360:Arabidopsis / Q000276:immunology* / Q000378:metabolism* / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005408:Flagellin / Q000276:immunology; D006031:Glycosylation; D008364:Mannosyltransferases / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology; D011956:Receptors, Cell Surface / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D011956:Receptors, Cell Surface; D005408:Flagellin; C000609965:ALG3 protein, Arabidopsis; D008364:Mannosyltransferases; D020928:Mitogen-Activated Protein Kinases
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