In the present work, we have studied the role of quorum-sensing regulatory systems in Rhizobium-legume symbiosis. Competition assays suggest that inactivation of quorum sensing systems significantly affects the competitiveness of Rhizobium leguminosarum bv. viciae UPM791 (Rl UPM791) when compared to other strains. Structural analysis through HPLC / mass spectrometry revealed that the signals produced by Rl UPM791 correspond to: C6-HSL, C7-HSL, C8-HSL and 3OH-C14-HSL; also, small amounts of C4-HSL have been detected. We are also analyzing the complex regulation of AHL signal molecules. We have evidence indicating that an Rl UPM791 plasmid (pUPM791d) participates in a regulatory network acting on the chromosomal system cinRI. We are using concurrent strategies (sequencing of pUPM791d and random mutagenesis) to identify the mechanism responsible for the control of pUPM791d over AHL production in Rl UPM791
