1LEM, EA 3514, Université Paris 7, Case 7069, 2 place Jussieu, 75251 Paris cedex 5, France; 2Laboratoire de Pathologie Végétale, UMR 217 INRA-INA-Paris VI, INA-PG, 16 rue Claude Bernard, 75231 Paris cedex 5, France
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Accepted 9 August 2006.
Erwinia amylovora is a gram-negative necrogenic bacterium causing fire blight of the Maloideae subfamily of Rosaceae such as apple and pear. It provokes progressive necrosis in aerial parts of susceptible host plants (compatible interaction) and a hypersensitive reaction (HR) when infiltrated in nonhost plants (incompatible interaction). The HrpNea harpin is a type three secretion system effector secreted by E. amylovora. This protein is involved in pathogenicity and HR-eliciting capacity of E. amylovora. In the present study, we showed that, in nonhost Arabidopsis thaliana cells, purified HrpNea induces cell death and H2O2 production, two nonhost resistance responses, but failed to induce such responses in host MM106 apple cells. Moreover, HrpNea induced an increase in anion current in host MM106 apple cells, at the opposite of the decrease of anion current previously shown to be necessary to induce cell death in nonhost A. thaliana cells. These results suggest that HrpNea induced
different signaling pathways, which could account for early induced compatible or incompatible interaction development.
The American Phytopathological Society, 2007