title: The pepper extracellular xyloglucan-specific endo-β-1,4-glucanase inhibitor protein gene, CaXEGIP1, is required for plant cell death and defense responses.
abstract: Plants produce various proteinaceous inhibitors to protect themselves against microbial pathogen attack. A xyloglucan-specific endo-β-1,4-glucanase inhibitor1 gene, CaXEGIP1, was isolated and functionally characterized in pepper (Capsicum annuum) plants. CaXEGIP1 was rapidly and strongly induced in pepper leaves infected with avirulent Xanthomonas campestris pv vesicatoria, and purified CaXEGIP1 protein significantly inhibited the hydrolytic activity of the glycoside hydrolase74 family xyloglucan-specific endo-β-1,4-glucanase from Clostridium thermocellum. Soluble-modified green fluorescent protein-tagged CaXEGIP1 proteins were mainly localized to the apoplast of onion (Allium cepa) epidermal cells. Agrobacterium tumefaciens-mediated overexpression of CaXEGIP1 triggered pathogen-independent, spontaneous cell death in pepper and Nicotiana benthamiana leaves. CaXEGIP1 silencing in pepper conferred enhanced susceptibility to virulent and avirulent X. campestris pv vesicatoria, accompanied by a compromised hypersensitive response and lowered expression of defense-related genes. Overexpression of dexamethasone:CaXEGIP1 in Arabidopsis (Arabidopsis thaliana) enhanced resistance to Hyaloperonospora arabidopsidis infection. Comparative histochemical and proteomic analyses revealed that CaXEGIP1 overexpression induced a spontaneous cell death response and also increased the expression of some defense-related proteins in transgenic Arabidopsis leaves. This response was also accompanied by cell wall thickening and darkening. Together, these results suggest that pathogen-inducible CaXEGIP1 positively regulates cell death-mediated defense responses in plants.
authors.affiliation: Laboratory of Molecular Plant Pathology, School of Life Sciences and Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Hyong Woo
authors.initials: HW
authors.lastname: Choi
authors.forename: Nak Hyun
authors.initials: NH
authors.lastname: Kim
authors.forename: Yeon Kyeong
authors.initials: YK
authors.lastname: Lee
authors.forename: Byung Kook
authors.initials: BK
authors.lastname: Hwang
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D002212:Capsicum / Q000235:genetics* / Q000276:immunology / Q000382:microbiology; D016923:Cell Death; D002473:Cell Wall / Q000276:immunology / Q000382:microbiology; D002480:Cellulase / Q000037:antagonists & inhibitors*; D048013:Acetivibrio thermocellus / Q000201:enzymology; D019295:Computational Biology / Q000379:methods; D003907:Dexamethasone / Q000494:pharmacology; D060467:Disease Resistance; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant; D049452:Green Fluorescent Proteins / Q000378:metabolism; D019697:Onions / Q000378:metabolism; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology; D057865:Plant Immunity; D018515:Plant Leaves / Q000276:immunology / Q000382:microbiology; D030821:Plants, Genetically Modified / Q000276:immunology / Q000382:microbiology; D020543:Proteome / Q000032:analysis; D012995:Solubility; D016959:Xanthomonas campestris / Q000276:immunology / Q000472:pathogenicity
chemical_list: D004791:Enzyme Inhibitors; D020543:Proteome; D049452:Green Fluorescent Proteins; D003907:Dexamethasone; D002480:Cellulase