Search for Ancestral Features in Genomes of bv. Strains Isolated from the Relict Legume .

is a relict leguminous plant growing in hard-to-reach habitats in the rocky highlands of the Caucasus and Middle East, and it is considered as the putative closest living relative of the last common ancestor (LCA) of the Fabeae tribe. Symbionts of belonging to bv. compose a discrete group that differs from the other strains, especially in the nucleotide sequences of the symbiotically specialised () genes. Comparison of the genomes of strains with the reference group composed of bv. strains isolated from and demonstrated that the vavilovia strains have a set of genomic features, probably indicating the important stages of microevolution of the symbiotic system. Specifically, symbionts of (considered as an ancestral group) demonstrated a scattered arrangement of genes (>90 kb cluster on p), with the location of T gene outside of the other operons, the presence of X and W, and the absence of chromosomal NOPQ copies. In contrast, the reference (derived) group harboured genes as a compact cluster (<60 kb) on a single p, lacking X and W, with T between N and O, and possessing chromosomal NOPQ copies. The TOM strain, obtained from nodules of the primitive "Afghan" peas, occupied an intermediate position because it has the chromosomal NOPQ copy, while the other features, the most important of which is presence of X and W, were similar to the strains. We suggest that genome evolution from the ancestral to the derived bv. groups follows the "gain-and-loss of genes" and the "compaction of cluster" strategies, which are common for the macro-evolutionary and micro-evolutionary processes. The revealed genomic features are in concordance with a relict status of the vavilovia strains, indicating that coexists with ancestral microsymbionts, which are presumably close to the LCA of bv. .