title: ATL9, a RING zinc finger protein with E3 ubiquitin ligase activity implicated in chitin- and NADPH oxidase-mediated defense responses.
abstract: Pathogen associated molecular patterns (PAMPs) are signals detected by plants that activate basal defenses. One of these PAMPs is chitin, a carbohydrate present in the cell walls of fungi and in insect exoskeletons. Previous work has shown that chitin treatment of Arabidopsis thaliana induced defense-related genes in the absence of a pathogen and that the response was independent of the salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signaling pathways. One of these genes is ATL9 ( = ATL2G), which encodes a RING zinc-finger like protein. In the current work we demonstrate that ATL9 has E3 ubiquitin ligase activity and is localized to the endoplasmic reticulum. The expression pattern of ATL9 is positively correlated with basal defense responses against Golovinomyces cichoracearum, a biotrophic fungal pathogen. The basal levels of expression and the induction of ATL9 by chitin, in wild type plants, depends on the activity of NADPH oxidases suggesting that chitin-mediated defense response is NADPH oxidase dependent. Although ATL9 expression is not induced by treatment with known defense hormones (SA, JA or ET), full expression in response to chitin is compromised slightly in mutants where ET- or SA-dependent signaling is suppressed. Microarray analysis of the atl9 mutant revealed candidate genes that appear to act downstream of ATL9 in chitin-mediated defenses. These results hint at the complexity of chitin-mediated signaling and the potential interplay between elicitor-mediated signaling, signaling via known defense pathways and the oxidative burst.
authors.affiliation: Department of Plant Biology, Carnegie Institution, Stanford, California, United States of America.
authors.forename: Marta
authors.initials: M
authors.lastname: Berrocal-Lobo
authors.forename: Sophia
authors.initials: S
authors.lastname: Stone
authors.forename: Xin
authors.initials: X
authors.lastname: Yang
authors.forename: Jay
authors.initials: J
authors.lastname: Antico
authors.forename: Judy
authors.initials: J
authors.lastname: Callis
authors.forename: Katrina M
authors.initials: KM
authors.lastname: Ramonell
authors.forename: Shauna
authors.initials: S
authors.lastname: Somerville
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D002686:Chitin / Q000378:metabolism*; D003517:Cyclopentanes / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009154:Mutation; D019255:NADPH Oxidases / Q000378:metabolism*; D054883:Oxylipins / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016335:Zinc Fingers / Q000235:genetics*
chemical_list: D003517:Cyclopentanes; D005030:Ethylenes; D054883:Oxylipins; D002686:Chitin; C011006:jasmonic acid; C036216:ethylene; D019255:NADPH Oxidases; C559062:ATL9 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases; D020156:Salicylic Acid