Characterization of high-frequency deletions in the iaa-containing plasmid, pIAA2, of Pseudomonas syringae pv. savastanoi.

The phytopathogenic bacterium Pseudomonas syringae pv. savastanoi causes olive and oleander knot disease. The bacterium induces the formation of tumorous galls by the synthesis and secretion of the plant hormones trans-zeatin riboside and indole-3-acetic acid into host intercellular spaces. An Italian oleander isolate, PB213, has been observed to lose the ability to synthesize IAA at high frequency, thus becoming non-pathogenic. The IAA genes, located on the 72-kb iaa-containing plasmid, pIAA2 were lost mainly due to two classes of deletions: 18 or 22 kb in length. Both classes of deletions had a common endpoint upstream of the IAA genes. The other endpoints were in areas that flanked the insertion sequence element IS51. The endpoints are in regions of repetitive DNA of at least 271 bp that have been designated a/b.