title: Apoplastic and cytoplasmic location of harpin protein Hpa1Xoo plays different roles in H2O2 generation and pathogen resistance in Arabidopsis.
abstract: Harpin proteins secreted by phytopathogenic bacteria have been shown to activate the plant defense pathway, which involves transduction of a hydrogen peroxide (H(2)O(2)) signal generated in the apoplast. However, the way in which harpins are recognized in the pathway and what role the apoplastic H(2)O(2) plays in plant defenses are unclear. Here, we examine whether the cellular localization of Hpa1(Xoo), a harpin protein produced by the rice bacterial leaf blight pathogen, impacts H(2)O(2) production and pathogen resistance in Arabidopsis thaliana. Transformation with the hpa1 (Xoo) gene and hpa1 (Xoo) fused to an apoplastic localization signal (shpa1 (Xoo)) generated h pa1 (Xoo)- and sh pa1 (Xoo)-expressing transgenic A . t haliana (HETAt and SHETAt) plants, respectively. Hpa1(Xoo) was associated with the apoplast in SHETAt plants but localized inside the cell in HETAt plants. In addition, Hpa1(Xoo) localization accompanied H(2)O(2) accumulation in both the apoplast and cytoplasm of SHETAt plants but only in the cytoplasm of HETAt plants. Apoplastic H(2)O(2) production via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) located in the plasma membrane is a common feature of plant defenses. In SHETAt plants, H(2)O(2) was generated in apoplasts in a NOX-dependent manner but accumulated to a greater extent in the cytoplasm than in the apoplast. After being applied to the wild-type plant, Hpa1(Xoo) localized to apoplasts and stimulated H(2)O(2) production as in SHETAt plants. In both plants, inhibiting apoplastic H(2)O(2) generation abrogated both cytoplasmic H(2)O(2) accumulation and plant resistance to bacterial pathogens. These results suggest the possibility that the apoplastic H(2)O(2) is subject to a cytoplasmic translocation for participation in the pathogen defense.
authors.affiliation: State Ministry of Education Key Laboratory of Integrated Management of Crop Pests, Nanjing Agricultural University, Nanjing, 210095, China.
authors.forename: Suling
authors.initials: S
authors.lastname: Sang
authors.forename: Xiaojie
authors.initials: X
authors.lastname: Li
authors.forename: Rong
authors.initials: R
authors.lastname: Gao
authors.forename: Zhenzhen
authors.initials: Z
authors.lastname: You
authors.forename: Beibei
authors.initials: B
authors.lastname: Lü
authors.forename: Peiqing
authors.initials: P
authors.lastname: Liu
authors.forename: Qixiang
authors.initials: Q
authors.lastname: Ma
authors.forename: Hansong
authors.initials: H
authors.lastname: Dong
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005798:Genes, Bacterial; D006861:Hydrogen Peroxide / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology; D030821:Plants, Genetically Modified; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014974:Xanthomonas / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity
chemical_list: D001425:Bacterial Outer Membrane Proteins; D011994:Recombinant Proteins; C087295:HrpZ protein, Pseudomonas syringae; D006861:Hydrogen Peroxide