title: pSymA-dependent mobilization of the Sinorhizobium meliloti pSymB megaplasmid.
abstract: Sinorhizobium meliloti 1021 carries two megaplasmids, pSymA of 1,354 kb and pSymB of 1,683 kb, which are essential in establishing symbiosis with its legume hosts and important for bacterial fitness in the rhizosphere. We have previously shown that pSymA is self-transmissible and that its conjugal functions are regulated by the transcriptional repressor RctA. Here, we show conjugal transfer of pSymB as an in trans mobilization event that requires the type IV secretion system encoded by pSymA. pSymB carries a functional oriT and an adjacent relaxase gene, traA2, that is also transcriptionally repressed by rctA. Both symbiotic megaplasmids would require the relaxase genes in cis with their respective oriTs to achieve the highest transfer efficiencies.
authors.affiliation: Plant-Bacteria Interactions Laboratory, Departamento Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Profesor Albareda 1, Granada, Spain.
authors.forename: Helena
authors.initials: H
authors.lastname: Blanca-Ordóñez
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Oliva-García
authors.forename: Daniel
authors.initials: D
authors.lastname: Pérez-Mendoza
authors.forename: María J
authors.initials: MJ
authors.lastname: Soto
authors.forename: José
authors.initials: J
authors.lastname: Olivares
authors.forename: Juan
authors.initials: J
authors.lastname: Sanjuán
authors.forename: Joaquina
authors.initials: J
authors.lastname: Nogales
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003227:Conjugation, Genetic; D004254:DNA Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal; D010957:Plasmids / Q000378:metabolism*; D018741:Replication Origin; D016962:Sinorhizobium meliloti / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C083180:Mob protein, Bacteria; D004254:DNA Nucleotidyltransferases; C110340:DNA relaxase