High-resolution mapping of YACs and the single-copy gene Hs1(pro)-1 on Beta vulgaris chromosomes by multi-colour fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) is a powerful approach for physic al mapping of DNA sequences along plant chromosomes. Nematode-resistant sug ar beets (Beta vulgaris) carrying a Beta procumbens translocation were inve stigated by FISH with two differentially labelled YACs originating from the translocation. At mitotic metaphases, the translocation was identified wit h both YACs in the terminal region on a pair of chromosomes. Meiotic chromo somes, representing a far more extended hybridization target, were used to determine the orientation of YACs with respect to chromosomal domains in co mbination with chromosomal landmark probes for telomeres and centromeres. T he in situ detection of plant single-copy sequences is technically difficul t, and the wild beet translocation was used to explore the potential resolu tion of the FISH approach and to introduce the chromosomal mapping of singl e-copy genes into genome analysis of Beta species. An internal fragment of the nematode resistance gene Hs1(pro-1), 684 bp long, was detected on both chromatids of different Beta chromosomes and represents one of the shortest unique DNA sequences localized on mitotic plant chromosomes so far. Compar ative chromosomal mapping of the 684 bp Hs1(pro-1) probe in the translocati on line, a monosomic addition line and in B. procumbens revealed the origin of the wild beet translocation leading to nematode-resistant sugar beets.