Exposure to host resistance drives evolution of bacterial virulence in plants; investigating the excision and mobility of genomic island PPHGI-1

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The ability of bacteria to infect animal and plant hosts is determined by proteins known as pathogenicity factors. These factors are encoded by genes, which are frequently found on mobile pieces of DNA known as genomic islands (GI). Transmission of GIs between bacteria is predicted to disseminate pathogenicity determinants amongst bacteria causing the spread of virulence. In plant pathogenic bacteria the acquisition or loss of pathogenicity determinants can result in a change of virulence. We have previously found that the pathogenicity determinant avrPphB resides on a GI designated PPHGI-1, which if deleted from the chromosome of the plant pathogen Pseudomonas syringae pathovar phaseolicola strain 1302A, causes a change in pathogenicity on differential cultivars of bean. Located on the GI are genes predicted to mediate the mobilisation of the GI as well as genes thought to be involved in conjugation of mobile elements from one bacterium to another. This proposal will investigate, using molecular techniques, the function of the genes predicted to mediate movement and conjugation of the PPHGI-1 carrying avrPphB. We hypothesise that these mobility determinants will be involved in movement and transmission of avrPphB. The research will help to elucidate ubiquitous mechanisms involved in the transfer of pathogenicity in plant and animal pathogens, a knowledge of which could impact on medicinal and agricultural treatments against pathogens.