Expression of viral EPS-depolymerase reduces fire blight susceptibility in transgenic pear.

Erwinia amylovora is the causal agent of fire blight of Maloideae. One of the main pathogenicity factors of this bacterium is the exopolysaccharide (EPS) of its capsule. In this paper, we used genetic transformation tools to constitutively express an EPS-depolymerase transgene in the pear (Pyrus communis L.) cv. Passe Crassane with the aim of decreasing its high susceptibility to fire blight. Expression of the depolymerase gene in 15 independent transgenic clones led, on average, to low depolymerase activity, although relatively high expression was observed at the transcriptional and translational levels. Only two of the transgenic clones (9X and 10M) consistently showed a decrease in fire blight susceptibility in vitro and in the greenhouse. These clones were also among the highest expressers of depolymerase at the RNA and enzyme activity levels. The correlation observed among all transgenic clones between depolymerase expression and fire blight resistance suggested the potential of this strategy.