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Medicago lupulina L. possesses a complex of valuable economic and biological traits: high adaptive ability to climatic and edaphic growing conditions, good nutrition and digestibility of green mass. The aim of this work was to study the chloroplast genome, which is associated with plant defense responses of M. lupulina L. var. vulgaris Koch, cultivar-population VIK32, line MlS-1, which is highly responsive to mycorrhization and forms a highly effective symbiosis with salt-sensitive strain Sinorhizobium meliloti L6-AK89. The studied complete chloroplast genome is a double-stranded circular DNA molecule of 118340 bp in length with an average GC composition of 34.18%. Short inverted repeats (IRa and IRb), presumably involved in chloroplast replication processes, are 1.8 times shorter in M. lupulina VIK32 than in M. lupulinaNC_042847. Two extended regions 12501 and 5001 bp in length, presumably introduced due to HGT, and the 7 regions containing short sequences showed similarity to sequences of 260 viruses (Identity 78–96%, E-value 5 × 10–33–4 × 10–3) were identified. In addition, a number of deletions, insertions, and SNPs are significantly differentiate the chloroplast genomes at the interspecies level, this suggestion requires further investigation. The cpDNA of the M. lupulina VIK32 was shown to be phylogenetically closely related to cpDNA of M. lupulinaNC_042847 and M. minima, but it was the most divergent from the putative common Medicago-Melilotus-Glycine ancestral cpDNA sequence. [ABSTRACT FROM AUTHOR]

Analysis of the structural polymorphism of eight genes in Sinorhizobium meliloti (nodA, nodB, nodC, and nodH, as well as betA, betB, betC, and betB2) involved in virulence control and salt tolerance, respectively, was carried out in native populations from two geographically distant areas of alfalfa diversity. These areas are located in the North Caucasian gene center of cultivated plants (NCG) and in the modern center of introgressive hybridization of alfalfa located next to the Aral Sea area (PAG) subjected to salinization. RFLP types (alleles) of the nod and bet genes, similar to those in the reference strain Rm1021 (A-type) and different from them (divergent, or D-type alleles) were revealed. The combinations for A- and D-type alleles of the aforementioned genes (analysis of the linkage disequilibrium, LD) were studied in both populations. It was shown that D-type alleles of the nod genes were two times more frequent in the NCG population, while D-type alleles of the bet genes were predominantly identified in the PAG population. At the same time, different combinations of D-type alleles of both the nod and bet genes prevailed in populations. For instance, in the case of the glycine betaine metabolism pathway, these were the betC and betB2 genes in NCG population and betB and betA genes in PAG population. The state of linkage disequilibrium was shown for 60.7% of combinations of alleles of the nod and bet genes in the S. meliloti strains from NCG and more than twice less in strains from the PAG population. It was concluded that clonal lines prevailed in NCG, while the PAG population of S. meliloti had a panmictic structure with revealed single clonal lines. [ABSTRACT FROM AUTHOR]