Tabtoxin biosynthetic gene cluster in Pseudomonas syringae pv. tabaci 6605 genomic island 1 (GI-1Pta6605) is required for severe disease symptoms

One of the genomic islands in Pseudomonas syringae pv. tabaci 6605 (GI-1 Pta 6605 ) has been identified as a pathogenicity island required for virulence because the deletion almost completely eliminated disease symptoms in inoculation tests at 4 × 10 5 CFU/ml. GI-1 Pta 6605 contains four cargo regions (CRs) named CR-1 to CR-4. The ∆CR-4 mutant did not produce tabtoxin like ∆GI-1 and disease symptoms did not develop in tobacco. However, it grew, although to a lesser extent than the wild-type strain. These results indicate that the tabtoxin biosynthetic gene cluster in GI-1 is required for virulence but not for establishment of compatibility.