title: Antagonistic action of harpin proteins: HrpWea from Erwinia amylovora suppresses HrpNea-induced cell death in Arabidopsis thaliana.
abstract: Harpins are proteins secreted by the type-three secretion system of phytopathogenic bacteria. They are known to induce a hypersensitive response (HR) in non-host plant leaf tissue. Erwinia amylovora, the fire blight pathogen of pear and apple trees, secretes two different harpins, HrpNea and HrpWea. In the present study, we showed that an Erwinia amylovora hrpWea mutant induces stronger electrolyte leakages in Arabidopsis thaliana foliar disks than the wild-type strain, thus suggesting that HrpWea could function as a HR negative modulator. We confirmed this result by using purified HrpWea and HrpNea. HrpWea has dual effects depending on its concentration. At 200 nM, HrpWea, like HrpNea, provoked the classical defense response--active oxygen species (AOS) production and cell death. However, at 0.2 nM, HrpWea inhibited cell death and AOS production provoked by HrpNea. HrpWea probably inhibits HrpNea-induced cell death by preventing anion channel inhibition, confirming that anion channel regulation is a determinant feature of the plant response to harpins. Collectively our data show that the HrpWea harpin can act antagonistically to the classical HrpNea harpin by suppressing plant defense mechanisms.
authors.affiliation: LEM, EA 3514, Université Paris Diderot, Case 7069, 2 place Jussieu, 75251 Paris cedex 5, France.
authors.forename: David
authors.initials: D
authors.lastname: Reboutier
authors.forename: Cécile
authors.initials: C
authors.lastname: Frankart
authors.forename: Joël
authors.initials: J
authors.lastname: Briand
authors.forename: Bernadette
authors.initials: B
authors.lastname: Biligui
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Rona
authors.forename: Minna
authors.initials: M
authors.lastname: Haapalainen
authors.forename: Marie-Anne
authors.initials: MA
authors.lastname: Barny
authors.forename: François
authors.initials: F
authors.lastname: Bouteau
mesh_terms: D017360:Arabidopsis / Q000378:metabolism* / Q000382:microbiology; D001425:Bacterial Outer Membrane Proteins / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D044084:Erwinia amylovora; D007473:Ion Channels / Q000378:metabolism; D027845:Malus / Q000382:microbiology; D010935:Plant Diseases; D018515:Plant Leaves / Q000378:metabolism* / Q000382:microbiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000187:drug effects*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D007473:Ion Channels; D017382:Reactive Oxygen Species; C075462:harpin protein, Erwinia amylovora