Progression of fire blight disease of apple and pear trees requires the causative agent Erwinia amylovora to coordinately express virulence traits and spread through host tissues (Piqué et al., 2015;Zhao et al., 2005). During infection, E. amylovora cells encounter several differing and hostile environments presented by specific host cell and tissue types that present distinct physical and biochemical challenges.Precise expression of genes involved in overcoming host defences and barriers under appropriate conditions leads to successful infection for E. amylovora.Multiple specific virulence factors are important for successful infection of apple and pear trees by E. amylovora (Kharadi et al.,