SPECIES-SPECIFIC EVOLUTION OF TELOMERIC AND RDNA REPEATS IN THE TOBACCO COMPOSITE GENOME

In order to investigate possible interactions between parental genomes in the composite genome of Nicotiana tabacum we have analyzed the org anization of telomeric (TTTAGGG)(n) and ribosomal gene (rDNA) repeats in the progenitor genomes Nicotiana sylvestris and Nicotiana tomentosi formis or Nicotiana otophora. Telomeric arrays in the Nicotiana specie s tested are heterogeneous in length ranging from 20 to 200 kb in N. s ylvestris, from 20 to 50 kb in N. tomentosiformis, from 15 to 100 kb i n N, otophora, and from 40 to 160 kb in N. tabacum. The patterns of rD NA repeats (18S, 5.8S, 25S RNA) appeared to be highly homogeneous and species-specific; no parental rDNA units corresponding to N. sylvestri s, N. tomentosiformis or N. otophora were found in the genome of N, ta bacum by Southern hybridization. The results provide evidence for a sp ecies-specific evolution of telomeric and ribosomal repeats in the tob acco composite genome.