Structural Polymorphism of Sinorhizobium meliloti Genes Related to Virulence and Salt Tolerance

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.