Tynkevich Y. Organization and evolution of 5S rDNA in the genus Rosa L.

The polymorphism, structural organization and evolution of 5S rDNA studied in genus Rosa. In the roses genomes two classes of 5S rDNA, which are identical in the coding regions, but demonstrate significant sequence difference in the IGS, were found. The divergence of these classes, which were called a and b, took place in the early stage of evolution of the genus. Later, in some diploid species the 5 rDNA repeats of b class were eventually lost. It was found that the 5S rDNA IGS is composed of alternating variable and conserved regions. The relative abundance of a and b 5S rDNA repeats was evaluated for eighteen Rosa specis. The level of cytosine methylation was measured for 5S rDNA repeats of both structural classes. It has been shown that the methylation level in the central part of IGS amounts to nearly 100%. The relative methylation level of ? and ? 5S rDNA repeats varies in different species and does not correlate with their taxonomic position or ploidy level. Obtained sequences of the 5S rDNA IGS were used for generation of phylodendrograms reflecting phylogenetic relatedness among Rosa species. The data confirmed hybridogenic nature of section Caninae and indicated that one of the parental forms of odd polyploids was a species, related to R. rugosa of section Cinnamomeae. Polyphyletic nature of traditionally defined sections such as Pimpinellifoliae, Synstylae and Cinnamomeae was demonstrated.