Grouping Pseudomonas syringae Strains by Comparing DNA Homology at the hrp Gene Cluster and Its Neighboring Regions

Abstract

We compared the structure and homology of the hrp gene cluster and its neighboring region for grouping Pseudomonas syringae pathovars. Cosmid clones selected from genomic libraries constructed for P. syringae pv. glycinea, pv. maculicola and pv. tabaci covered a genomic region of more than 80kb that was homologous to hrp genes and neighboring regions in pv. phaseolicola. Comparison of restriction sites and homologies of this large genomic region revealed that the structures of the hrp gene clusters of pv. glycinea, pv. phaseolicola and pv. tabaci closely resemble each other, whereas that of pv. maculicola is distinct from those of the other three pathovars. Hybridization probes derived from pv. phaseolicola and pv. maculicola were used for grouping 32 pathovars of P. syringae by Southern hybridization analysis. Patterns of hybridization signal strength suggested that P. syringae pathovars can be classified into at least the following three groups: strains having strong homologies to probes from pv. phaseolicola (group I), strains having strong homologies to probes from pv. maculicola (group II) and strains having moderate to no homology to probes from either of the pathovars (group U).