title: Loss-of-function mutations in chitin responsive genes show increased susceptibility to the powdery mildew pathogen Erysiphe cichoracearum.
abstract: Chitin is a major component of fungal walls and insect exoskeletons. Plants produce chitinases upon pathogen attack and chito-oligomers induce defense responses in plants, though the exact mechanism behind this response is unknown. Using the ATH1 Affymetrix microarrays consisting of about 23,000 genes, we examined the response of Arabidopsis (Arabidopsis thaliana) seedlings to chito-octamers and hydrolyzed chitin after 30 min of treatment. The expression patterns elicited by the chito-octamer and hydrolyzed chitin were similar. Microarray expression profiles for several genes were verified via northern analysis or quantitative reverse transcription-PCR. We characterized T-DNA insertion mutants for nine chito-oligomer responsive genes. Three of the mutants were more susceptible to the fungal pathogen, powdery mildew, than wild type as measured by conidiophore production. These three mutants included mutants of genes for two disease resistance-like proteins and a putative E3 ligase. The isolation of loss-of-function mutants with enhanced disease susceptibility provides direct evidence that the chito-octamer is an important oligosaccharide elicitor of plant defenses. Also, this study demonstrates the value of microarray data for identifying new components of uncharacterized signaling pathways.
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama 35487-0344, USA. kramonel@bama.ua.edu
authors.forename: Katrina
authors.initials: K
authors.lastname: Ramonell
authors.forename: Marta
authors.initials: M
authors.lastname: Berrocal-Lobo
authors.forename: Serry
authors.initials: S
authors.lastname: Koh
authors.forename: Jinrong
authors.initials: J
authors.lastname: Wan
authors.forename: Herb
authors.initials: H
authors.lastname: Edwards
authors.forename: Gary
authors.initials: G
authors.lastname: Stacey
authors.forename: Shauna
authors.initials: S
authors.lastname: Somerville
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism* / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000378:metabolism; D001203:Ascomycota / Q000502:physiology*; D002686:Chitin / Q000502:physiology*; D015536:Down-Regulation; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D025301:Hyphae / Q000378:metabolism; D007113:Immunity, Innate; D009154:Mutation; D010641:Phenotype; D010935:Plant Diseases; D015854:Up-Regulation
chemical_list: D029681:Arabidopsis Proteins; D002686:Chitin