Expression of a bacterial effector, harpin N, causes increased resistance to fire blight in Pyrus communis

The rapid and effective activation of disease resistance responses is essential for plant defense against pathogen attack. These responses are initiated when pathogen-derived molecules (elicitors) are recognized by the host. In order to create novel mechanisms for fire blight resistance in pear, we have generated transgenic pears expressing the elicitor harpin Nea from Erwinia amylovora under the control of the constitutive promoter CaMV35S. The transient expression of hrpN Ea in pear cells did not provoke any apparent damage. Therefore, stable constitutive expression of hrpN Ea was studied in seventeen transgenic clones of the very susceptible cultivar "Passe Crassane.” Most transgenic clones displayed significant reduction of susceptibility to fire blight in vitro when inoculated by E. amylovora, which was positively correlated to their degree of expression of the transgene hrpN Ea . These results indicate that ectopic expression of a bacterial elicitor such as harpin Nea is a promising way to improve pear resistance to fire blight