Atl9, a ring zinc finger protein with e3 ubiquitin ligase activity implicated in chitin- and nadph oxidase- mediated defense responses

ATL9, a RING Zinc Finger Protein with E3 Ubiquitin Ligase Activity Implicated in Chitin- and NADPH OxidaseMediated Defense Responses
Marta Berrocal-Lobo1¤b, Sophia Stone3, Xin Yang2, Jay Antico2, Judy Callis3, Katrina M. Ramonell2*, Shauna Somerville1¤a
1 Department of Plant Biology, Carnegie Institution, Stanford, California, United States of America, 2 Department of Biological Sciences,University of Alabama, Tuscaloosa, Alabama, United States of America, 3 Section of Molecular and Cellular Biology, University of California Davis, Davis, California, United States of America

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 insectexoskeletons. 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 ATL9has 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 defenseresponse 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. Theseresults 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.
Citation: Berrocal-Lobo M, Stone S, Yang X, Antico J, Callis J, et al. (2010) ATL9, a RING Zinc Finger Protein with E3 Ubiquitin Ligase Activity Implicated in Chitinand NADPH Oxidase-Mediated Defense Responses. PLoSONE 5(12): e14426. doi:10.1371/journal.pone.0014426 Editor: Daniel J. Kliebenstein, University of California, United States of America Received June 24, 2010; Accepted November 23, 2010; Published December 23, 2010 Copyright: ß 2010 Berrocal-Lobo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Marta Berrocal-Lobo was supported by the Carnegie Institution of Washington and a postdoctoral fellowship from the Secretaria de Estado de Educacion y Universidades and Fondo Social Europeo, MECD/Fullbright (Spain). Katrina M. Ramonell was supported by the University of Alabama and by grants from theNational Institutes of Health (grant no. 1-R15-GM073630-01) and the U.S. Department of Agriculture (grant no. 2007-01652 to K.M.R.). This work was supported in part by the National Science Foundation and the Carnegie Institution. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors havedeclared that no competing interests exist. * E-mail: kramonel@bama.ua.edu ¤a Current address: Energy Biosciences Institute, University of California, Berkeley, California, United States of America ´ ´cnica de Madrid, Pozuelo ´ ¤b Current address: Centro de Biotecnologıa y Genomica de Plantas (CBGP), (UPM-INIA), Campus de Montegancedo, Universidad Polite ´ de Alarcon, Madrid, Spain

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