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Vavilovia formosa 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 Vavilovia belonging to Rhizobium leguminosarum bv. viciae compose a discrete group that differs from the other strains, especially in the nucleotide sequences of the symbiotically specialised ( sym ) genes. Comparison of the genomes of Vavilovia strains with the reference group composed of R. leguminosarum bv. viciae strains isolated from Pisum and Vicia 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 Vavilovia (considered as an ancestral group) demonstrated a scattered arrangement of sym genes (>90 kb cluster on p Sym ), with the location of nod T gene outside of the other nod operons, the presence of nod X and fix W, and the absence of chromosomal fix NOPQ copies. In contrast, the reference (derived) group harboured sym genes as a compact cluster (<60 kb) on a single p Sym , lacking nod X and fix W, with nod T between nod N and nod O, and possessing chromosomal fix NOPQ copies. The TOM strain, obtained from nodules of the primitive "Afghan" peas, occupied an intermediate position because it has the chromosomal fix NOPQ copy, while the other features, the most important of which is presence of nod X and fix W, were similar to the Vavilovia strains. We suggest that genome evolution from the ancestral to the derived R. leguminosarum bv. viciae groups follows the "gain-and-loss of sym genes" and the "compaction of sym 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 V. formosa coexists with ancestral microsymbionts, which are presumably close to the LCA of R. leguminosarum bv. viciae ., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

5-hydroxymethylcytosine (5hmC) is an oxidative derivative of 5-methylcytosine (5mC). Recent studies have revealed a sharp difference in the levels of 5hmC in 2 opposite DNA strands of a given chromosome and a chromosome-wide cell-to-cell variability in mammalian cells. This asymmetric 5hmC distribution was found in cultured cells, which may not fully mimic in vivo epigenetic processes. We have checked whether inter-chromosome and inter-cell variability of 5hmC patterns is typical for noncultured human cells. Using indirect immunofluorescence, we analyzed the localization of 5hmC and its co-distribution with 5mC on direct preparations of mitotically active cells from human embryonic lung and chorionic cytotrophoblast samples. We demonstrated 3 types of chromosomes according to the 5hmC accumulation pattern: hydroxymethylated (5hmC in both sister chromatids), hemihydroxymethylated (5hmC in only 1 sister chromatid), and nonhydroxymethylated ones. Each accumulation type was not specific to any particular chromosome, resulting in different 5hmC patterns between homologous chromosomes, among chromosomes within each metaphase plate, among metaphases in one tissue, and between the tissues. The 5mC distribution was stable: chromosomes were methylated in R-bands and, especially in embryonic lung cells, in the heterochromatic regions 1q12, 9q12, and 16q11.2. Our results provide the first evidence of inter-cell and inter-chromosome variability of 5hmC patterns in human noncultured embryonic and extraembryonic cells., (© 2018 S. Karger AG, Basel.)