Characterization of plasmids encoding the phytotoxin coronatine in Pseudomonas syringae

Coronatine (COR) is a nonhost-specific phytotoxin that substantially contri butes to the virulence of several pathovars (pvs.) of Pseudomonas syringae. The COR gene cluster in P. syringae is generally plasmid-encoded in pvs. a tropurpurea, glycinea, morsprunorum, and tomato but chromosomally encoded i n pv. maculicola In the present study, we investigated whether the COR plas mids in four pathovars shared other traits including self-transmissibility, conserved oriV/par loci, and insertion sequences (ISs) known to reside on other plasmids in P, syringae. Three COR plasmids were shown to be self-tra nsmissible, and all COR plasmids shared a related oriV/par region. Two COR plasmids hybridized to IS801, an IS element widely distributed in P, syring ae. Further analysis of p4180A, a 90-kb COR plasmid in P. syringae pv. glyc inea, indicated that multiple copies of IS801 were present on this plasmid, and all copies mapped outside the COR gene cluster. Sequence analysis of t he region adjacent to the COR gene cluster in p4180A indicated the presence of additional IS elements including IS870, IS51, and IS1240. The IS elemen ts borne on p4180A may have contributed to horizontal transfer of the COR g ene cluster and the evolution of the COR biosynthetic pathway. (C) 1999 Aca demic Press.