HIGH-RESOLUTION FISH AND PFGE ANALYSES DEMONSTRATE BREAKDOWN OF TELOMERE REPEATS IN A SOMATIC TOMATO (+) POTATO HYBRID AND ITS BACK-CROSS DERIVATIVES

¹ Department of Biomolecular Sciences, Laboratory of Genetics, Wageningen University Research Centre, Dreijenlaan 2, 6703 HA Wageningen, The Netherlands

² Department of Biomolecular Sciences, Laboratory of Molecular Biology, Wageningen University Research Centre, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands

³ Department of Plant Sciences, Laboratory of Plant Breeding, Wageningen University Research Centre, Lawickse Allee 166, 6709 HA Wageningen, The Netherlands

A hexaploid somatic tomato (+) potato hybrid, obtained by fusing tomato and potato protoplasts, was backcrossed with tetraploid potato for the production of BC₁ and BC₂ families. We analysed the molecular size of the telomere repeat [TTTAGGG]n and the tomato specific satellite repeat TGR1 in one of the hybrids, its BC₁ and BC₂ plants using PGFE of high molecular weight DNA and Southern hybridisation. A dramatic decrease of telomere length and the disappearance of TGR1 sequences from tomato chromosomes was observed in the hybrid and the backcross generations. Additional cytogenetic evidence for the disappearance of the TGR1 was obtained by Fluorescence in situ hybridisations (FISH) of TGR1 to mitotic metaphase complements. High resolution FISH to extended DNA fibres confirmed a significant reduction of telomere repeat arrays in the somatic hybrid and backcross plants. In addition, tracks of TGR1 with an adjacent telomere repeat (TR), which were normal for the tomato parent, could not be found in the hybrids. The results indicate that telomeres in the somatic hybrids become particularly instable giving rise to breakage of TRs and TR/TGR1 combinations. The significance of this phenomenon for genome dynamics in interspecific hybrids are discussed.