Boundaries for Conjugative Transfer of Rhizobial Plasmids: Restraining and Releasing Factors

SUSANA BROM; MARIANO PISTORIO; DAVID ROMERO; GONZALO A. TORRES TEJERIZO

Plasticity in Plant-Growth-Promoting and Phytopathogenic Bacteria

Springer-Verlag New York

Año: 2014; p. 43 - 54

Rhizobia are a very interesting group of bacteria, able to differentiateinto nitrogen-fixing bacteroids inside nodules, formed through theirsymbiotic interaction with the roots of leguminous plants. Most ofthe bacterial genetic information required for the establishment ofthe symbiosis and nitrogen fixation is usually localized on plasmids,called symbiotic (pSym). In addition to a pSym, the genomes ofrhizobia may carry up to 60 % of their sequences in a variable numberof plasmids. In general, plasmids are considered elements likely toperform horizontal gene transfer through conjugation. Analysis of theconjugation ability of rhizobial plasmids has revealed the participationof an assortment of regulatory elements, including quorum-sensing,RctA-mediated repression, and other recently described modulators.In addition to which regulators are present in a strain, their genomiclocalization is also a significant factor influencing the scope of plasmidtransfer. Integrating the available data, we propose that plasmid transferis delimited by a complex set of intra- and inter-replicon interactions,which respond to specific environmental signals.