Résumé
Fire blight caused by the bacteria Erwinia amylovora is one of the most important diseases of pear. This causal agent produces a siderophore (desferrioxamine), which was identified as one of its virulence factors. This protein enables the bacteria to overcome conditions of iron limitation encountered in host tissues, and may also protect the bacteria against active oxygen species. Previous experiments indicate that the use of an iron chelator protein, encoded by the bovine lactoferrin gene, reduces fire blight symptoms in some transgenic pear clones. The aim of the present work is to test the ability of a more efficient iron chelator, plant ferritin, to reduce fire blight susceptibility in pear. In the literature, ferritin genes have been overexpressed under the control of a constitutive promoter in different transgenic plant species for various purposes. In several cases, the constitutive expression of ferritin produced negative effects such as reduced growth and chlorophyll content. Therefore, we decided to place the exogenous ferritin gene from pea under the control of a pathogen inducible promoter (sgd24) in comparison with a constitutive promoter (CaMV 35S). Two pear varieties, 'Conference' (CF) and 'Passe-Crassane' (PC) were transformed using both constructs. Transformation rates depended on variety and construct. They were respectively of 12 and 4.3% for CF and PC using the sgd24-ferritin construct. Only PC was transformed with the 35S-ferritin construct, with a transformation rate of 2%. First analyses of the transgenic clones by RT-PCR showed the expression of pea ferritin in both constructs and in all clones. The transgenic clones were acclimatized in greenhouse and exhibited normal growth. Quantification of ferritin gene expression, ferritin protein accumulation, and evaluation of fire blight resistance are underway.