Functional characterization of the adenine transporter EaAdeP from the fire blight pathogen Erwinia amylovora and its effect on disease establishment in apples and pears

Erwinia amylovora is the causal agent of fire blight, an economically important disease of apples and pears. As part of the infection process, Er. amylovora propagates on different plant tissues each with distinct nutrient environments. Here, the biochemical properties of the Er. amylovora adenine permease (EaAdeP) are investigated. Heterologous expression of EaAdeP in nucleobase transporter-deficient Escherichia coli strains, coupled with radiolabel uptake studies, revealed that EaAdeP is a high affinity adenine transporter with a Km of 0.43 ± 0.09 μM. Both Es. coli and Er. amylovora carrying extra copies of EaAdeP are sensitive to growth on the toxic analog 8-azaadenine. EaAdeP is expressed during immature pear fruit infection. Immature pear and apple fruit virulence assays reveal that an E. amylovora ΔadeP::Camr mutant is still able to cause disease symptoms, however, with growth at a lower level, indicating that external adenine is utilized in disease establishment.