Apoplastic and cytoplasmic location of harpin protein Hpa1Xoo plays different roles in H2O2 generation and pathogen resistance in Arabidopsis

• Published in: Plant molecular biology Vol. 79; no. 4-5; pp. 375 - 391
• Main Authors: Sang, Suling, Li, Xiaojie, Gao, Rong, You, Zhenzhen, Lü, Beibei, Liu, Peiqing, Ma, Qixiang, Dong, Hansong
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.07.2012
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - microbiology; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Biochemistry; Biological Transport, Active; Biomedical and Life Sciences; Cell Membrane - metabolism; Cytoplasm - metabolism; Extracellular Space - metabolism; Genes, Bacterial; Hydrogen Peroxide - metabolism; Life Sciences; Plant Diseases - microbiology; Plant Pathology; Plant Sciences; Plants, Genetically Modified; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Xanthomonas - genetics; Xanthomonas - metabolism; Xanthomonas - pathogenicity; H; Hpa1; Plant defenses; Harpin; Cytoplasmic translocation; O
• ISSN: 0167-4412; 1573-5028; 1573-5028
• DOI: 10.1007/s11103-012-9918-x

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 - e xpressing t ransgenic 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.