Two native plasmids of Pseudomonas syringae pathovar tomato strain PT23 share a large amount of repeated DNA, including replication sequences
Murillo Martínez, Jesús
Keen, Noel T.
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Strain PT23 of Pseudomonas syringae pv, tomato contains four native plasmids, designated A, B, C, and D. By DNA hybridization of genomic and plasmid DNA digests from the wild type and a plasmid-cured strain, we determined that c. 61 kb (c. 74%) of pPT23B is repeated in pPT23A and only c. 17 kb (c. 21%) is in single copy in strain PT23. pPT23B also contains DNA repeated in the chromosome that occurs in three DNA fragments of 0.6, 4.6, and 9.6 kb that might be transposable elements. Additionally, the 9.6 kb fragment also shares sequences with the three other plasmids of strain PT23. By DNA hybridization with the origin of replication from a native plasmid of P. syringae pv. syringae and in vivo replication tests, we identified the origins of replication of plasmids A, B, and D and showed that they cross-hybridize. The putative par region from pPT23 A has also been identified and is not conserved in the other three native plasmids from strain PT23. By using the defined minimal origin of replication from pPT23 A as a probe, we showed that it is highly conserved in 14 strains belonging to nine different pathovars of P. syringae and that as many as five different native plasmids with closely related origins of replication coexist in the same cell. The duplication and reorganization of plasmids might therefore occur at high frequency and could be responsible for the existence of large numbers of native plasmids in P. syringae strains.
Replicon, PFP plasmids, repA, Replication initiator protein gene, Duplicated plasmids, Origin of replication, Plant pathogen
Molecular Microbiology (1994) 12(6), 941-950
Universidad Pública de Navarra. Departamento de Producción Agraria / Nafarroako Unibertsitate Publikoa. Nekazaritza Ekoizpena Saila
J.M. was supported, in part, by grants 93-258 (DGICYT) and PF90-6984578 from the Ministerio de Educación y Ciencia, Spain. This work was supported by National Science Foundation Grant MCB-9005388-02.