Exclusive localization of tandem repetitive sequences in subtelomeric heterochromatin regions of Leymus racemosus (Poaceae, Triticeae).

Two kinds of tandem repetitive sequences were isolated from Leymus racemosus (Lam.) Tzvelev. One of them was classified in the 350-bp family originally isolated from Secale. The other was a novel repetitive sequence family, named 'TaiI family', which consisted of a repeat unit of 570 bp. Fluorescence in-situ hybridization of the chromosomes of L. racemosus indicated that both families were located in subtelomeric heterochromatin and that the 350-bp family and TaiI family occupied different heterochromatin regions. In addition, even homologous chromosomes did not show the same patterns of TaiI and 350-bp families. The combination of these two families of repetitive sequences, together with Afa-family sequences and rDNAs, helps to identify the ten homologous chromosome pairs of L. racemosus. From these data, we proposed a karyotype of L. racemosus and compared it with other karyotypes already reported.