GLOBAL REGULATION IN ERWINIA SPECIES BY ERWINIA-CAROTOVORA RSMA, A HOMOLOG OF ESCHERICHIA-COLI CSRA - REPRESSION OF SECONDARY METABOLITES, PATHOGENICITY AND HYPERSENSITIVE REACTION

Our previous studies revealed that rsmA of Erwinia carotovora subsp. c arotovora strain 71 suppressed the synthesis of the cell density (quor um) sensing signal N-(3-oxohexanoyl)-L-homoserine lactone, the product ion of extracellular enzymes and tissue macerating ability in soft-rot ting Erwinia species and that homologues of this negative regulator ge ne were present in other Erwinia species. Northern blot data presented here demonstrate that rsmA and rsmA-like genes are also expressed in soft-rotting and non-soft-rotting Erwinia spp, such as E. amylovora, E . carotovora subsp. atroseptica, E. carotovora subsp, betavasculorum, E. carotovora subsp, carotovora, E. chrysanthemi, E. herbicola and E. stewarlii. A low-copy plasmid carrying rsmA of E. carotovora subsp. ca rotovora strain 71 caused suppression of antibiotic production in E. c arotovora subsp. betavasculorum, flagellum formation in E. carotovora subsp. carotovora, carotenoid production in E. herbicola and E. stewar tii, and indigoidine production in E. chrysanthemi. In E. amylovora, r smA of E. carotovora subsp. carotovora suppressed the elicitation of t he hypersensitive reaction in tobacco leaves and the production of dis ease symptoms in apple shoots, in addition to repressing motility and extracellular polysaccharide production. We conclude that rsmA homolog ues function as global regulators of secondary metabolic pathways as w ell as factors controlling host interaction of Erwinia species.