Sinorhizobium melilotiSymbiosisMedicago sativaSinorhizobiumMedicago truncatulaNitrogen FixationBacterial ProteinsSinorhizobium frediiGene Expression Regulation, BacterialMedicagoPlant Root NodulationMutationGenes, BacterialRoot Nodules, PlantMolecular Sequence DataBacteriaRhizobiumEscherichia coliRhizobiaceaePolysaccharides, BacterialVirulencePlant RootsGene DeletionVirulence FactorsDNA, BacterialRhizobium leguminosarumFabaceaeMelilotusGenetic Complementation TestMutagenesis, InsertionalLuteolinSequence Analysis, DNA