title: Resistance to citrus canker induced by a variant of Xanthomonas citri ssp. citri is associated with a hypersensitive cell death response involving autophagy-associated vacuolar processes.
abstract: Xanthomonas citri ssp. citri (X. citri) is the causal agent of Asiatic citrus canker, a disease that seriously affects most commercially important Citrus species worldwide. We have identified previously a natural variant, X. citri AT, that triggers a host-specific defence response in Citrus limon. However, the mechanisms involved in this canker disease resistance are unknown. In this work, the defence response induced by X. citri ATwas assessed by transcriptomic, physiological and ultrastructural analyses, and the effects on bacterial biofilm formation were monitored in parallel. We show that X. citri ATtriggers a hypersensitive response associated with the interference of biofilm development and arrest of bacterial growth in C. limon. This plant response involves an extensive transcriptional reprogramming, setting in motion cell wall reinforcement, the oxidative burst and the accumulation of salicylic acid (SA) and phenolic compounds. Ultrastructural analyses revealed subcellular changes involving the activation of autophagy-associated vacuolar processes. Our findings show the activation of SA-dependent defence in response to X. citri ATand suggest a coordinated regulation between the SA and flavonoid pathways, which is associated with autophagy mechanisms that control pathogen invasion in C. limon. Furthermore, this defence response protects C. limon plants from disease on subsequent challenges by pathogenic X. citri. This knowledge will allow the rational exploitation of the plant immune system as a biotechnological approach for the management of the disease.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR)-Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Área Virología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario (UNR), Ocampo y Esmeralda s/n, Rosario, S2000FHN, Argentina.
authors.forename: Roxana A
authors.initials: RA
authors.lastname: Roeschlin
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR)-Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Área Virología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario (UNR), Ocampo y Esmeralda s/n, Rosario, S2000FHN, Argentina.
authors.forename: María A
authors.initials: MA
authors.lastname: Favaro
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR)-Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Área Virología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario (UNR), Ocampo y Esmeralda s/n, Rosario, S2000FHN, Argentina.
authors.forename: María A
authors.initials: MA
authors.lastname: Chiesa
authors.affiliation: Laboratorio de Fisiología Vegetal, Departamento de Ciencias Naturales, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Ruta 36 Km. 601, Río Cuarto X5804ZAB, Córdoba, Argentina.
authors.forename: Sergio
authors.initials: S
authors.lastname: Alemano
authors.affiliation: Instituto de Ciencia y Tecnología Dr. Cesar Milstein, Fundación Pablo Cassará-CONICET, Saladillo 2468, Ciudad de Buenos Aires, C1440FFX, Argentina.
authors.forename: Adrián A
authors.initials: AA
authors.lastname: Vojnov
authors.affiliation: Instituto de Tecnología Agroindustrial del Noroeste Argentino (ITA-NOA), Estación Experimental Agroindustrial Obispo Colombres (EEAOC)-CONICET, Av. William Cross 3150, Las Talitas, Tucumán, T4101XAC, Argentina.
authors.forename: Atilio P
authors.initials: AP
authors.lastname: Castagnaro
authors.affiliation: Instituto de Tecnología Agroindustrial del Noroeste Argentino (ITA-NOA), Estación Experimental Agroindustrial Obispo Colombres (EEAOC)-CONICET, Av. William Cross 3150, Las Talitas, Tucumán, T4101XAC, Argentina.
authors.forename: María P
authors.initials: MP
authors.lastname: Filippone
authors.affiliation: Citrus Research and Education Center (CREC), University of Florida, 700 Experiment Station Rd., Lake Alfred, FL, 33850, USA.
authors.forename: Frederick G
authors.initials: FG
authors.lastname: Gmitter
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas (IBMCP), Universidad Politécnica de Valencia (UPV)-Consejo Superior de Investigaciones Científicas (CSIC), Ciudad Politécnica de la Innovación (CPI), Ed. 8E, C/Ingeniero Fausto Elio s/n, Valencia, 46022, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Gadea
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR)-Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Área Virología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario (UNR), Ocampo y Esmeralda s/n, Rosario, S2000FHN, Argentina.
authors.forename: María R
authors.initials: MR
authors.lastname: Marano
mesh_terms: D001343:Autophagy / Q000502:physiology; D018441:Biofilms; D002957:Citrus / Q000382:microbiology*; D018506:Gene Expression Regulation, Plant; D010935:Plant Diseases / Q000382:microbiology*; D057865:Plant Immunity / Q000502:physiology; D020156:Salicylic Acid / Q000378:metabolism; D014974:Xanthomonas / Q000472:pathogenicity*
chemical_list: D020156:Salicylic Acid
keywords: autophagy; biofilm formation; biological control; citrus canker resistance; hypersensitive response; salicylic acid; secondary metabolites