Divergent Evolution of Symbiotic Bacteria: Rhizobia of the Relic Legume Vavilovia formosa Form an Isolated Group within Rhizobium leguminosarum bv. viciae

Comparative sequence analysis of symbiotic genes ( nod A, nod C, nod D, nif H), which are elements of accessory component of the rhizobial genome, demonstrated that the strains of Rhizobium leguminosarum bv. viciae , isolated from the nodules of a relic legume, Vavilovia formosa , the closest relative of hypothetical common ancestor of the tribe Fabeae, represented a group separated from the strains of R. leguminosarum bv. viciae , isolated from other representatives of this tribe ( Vicia, Lathyrus, Pisum, Lens ). No isolation was observed relative to the genes representing the core component of the rhizobial genome (16S rDNA, ITS, gln II) or relative to host specificity of the rhizobia. The data obtained suggest that sequence divergence of symbiotic genes marks the initial stage of sympatric speciation, which can be classified as the isolation of the relic “ vaviloviae ” symbiotype, a possible evolutionary precursor of the “ viciae ” biotype.