title: Characterization of Arabidopsis mur3 mutations that result in constitutive activation of defence in petioles, but not leaves.
abstract: A screen was established for mutants in which the plant defence response is de-repressed. The pathogen-inducible isochorismate synthase (ICS1) promoter was fused to firefly luciferase (luc) and a homozygous transgenic line generated in which the ICS1:luc fusion is co-regulated with ICS1. This line was mutagenized and M(2) seedlings screened for constitutive ICS1:luc expression (cie). The cie mutants fall into distinct phenotypic classes based on tissue-specific localization of luciferase activity. One mutant, cie1, that shows constitutive luciferase activity specifically in petioles, was chosen for further analysis. In addition to ICS1, PR and other defence-related genes are constitutively expressed in cie1 plants. The cie1 mutant is also characterized by an increased production of conjugated salicylic acid and reactive oxygen intermediates, as well as spontaneous lesion formation, all confined to petiole tissue. Significantly, defences activated in cie1 are sufficient to prevent infection by a virulent isolate of Hyaloperonospora parasitica, and this enhanced resistance response protects petiole tissue alone. Furthermore, cie1-mediated resistance, along with PR gene expression, is abolished in a sid2-1 mutant background, consistent with a requirement for salicylic acid. A positional cloning approach was used to identify cie1, which carries two point mutations in a gene required for cell wall biosynthesis and actin organization, MUR3. A mur3 knockout mutant also resists infection by H. parasitica in its petioles and this phenotype is complemented by transformation with wild-type MUR3. We propose that perturbed cell wall biosynthesis may activate plant defence and provide a rationale for the cie1 and the mur3 knockout phenotypes.
authors.affiliation: Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich, Norfolk NR47UH, UK.
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Tedman-Jones
authors.forename: Rita
authors.initials: R
authors.lastname: Lei
authors.forename: Florence
authors.initials: F
authors.lastname: Jay
authors.forename: Georgina
authors.initials: G
authors.lastname: Fabro
authors.forename: Xuemei
authors.initials: X
authors.lastname: Li
authors.forename: Wolf-Dieter
authors.initials: WD
authors.lastname: Reiter
authors.forename: Charles
authors.initials: C
authors.lastname: Brearley
authors.forename: Jonathan D G
authors.initials: JD
authors.lastname: Jones
mesh_terms: D000199:Actins / Q000378:metabolism; D000483:Alleles; D017360:Arabidopsis / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D017343:Genes, Plant; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D007113:Immunity, Innate; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D018515:Plant Leaves / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D018749:RNA, Plant / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020156:Salicylic Acid / Q000378:metabolism
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; D018749:RNA, Plant; D017382:Reactive Oxygen Species; D005700:Galactosyltransferases; C478982:MUR3 protein, Arabidopsis; D019751:Intramolecular Transferases; C058486:isochorismate synthase; D020156:Salicylic Acid