Fire blight, one of most egregious bacterial diseases of apple and pear trees, is caused by Erwinia amylovora. Our project identifies E. amylovora mutants that are not able to cause disease. One mutation was found in the rlsA gene, which is responsible for the regulation of the production of levansucrase, a polysaccharide. This project will help us understand previously unknown roles of the rlsA gene and how it contributes to disease development in the plant.