GENETICS AND COMPLEMENTATION OF DNA REGIONS INVOLVED IN AMYLOVORAN SYNTHESIS OF ERWINIA AMYLOVORA AND STEWARTAN SYNTHESIS OF ERWINIA STEWARTII

Erwinia amylovora and Erwinia stewartii form similar exopolysaccharide (EPS) capsules, which are the products of the ams and cps gene clusters, respectively.
Nucleotide sequence analysis has indicated that these DNA regions share many common functions.
Mutants in ams and cps genes are nonpathogenic and can also be heterologously complemented by EPS genes from the other species.
Depending on the chromosomal mutation, restoration of EPS synthesis in the foreign host requires a set of cloned ams or cps genes.
The nature of the EPS produced by the merodiploids was determined by degradation with a bacteriophage EPS-depolymerase specific for stewartan, binding to an amylovoran-specific lectin, compositional analysis, and methylation analysis.
The ams mutants complemented with the cps cluster produced stewartan and lost virulence on pear slices.
The cps mutants complemented with the ams cluster produced amylovoran and regained virulence to corn seedlings.
An exception was a complemented cpsK mutant that produced stewartan.
These results suggest a requirement for specific sugar residues in capsules of E. amylovora in order to escape recognition by plant defenses.

VII International Workshop on Fire Blight

F. Bernhard, D. Schullerus, P. Bellemann, K. Geider, D.R. Majerczak, D.L. Coplin, M. Nimtz

https://doi.org/10.17660/ActaHortic.1996.411.53