The technique of chromosomal orientation and direction fluorescence in situ hybridization (COD-FISH) was adapted for plant chromosomes in order to study long-range organization of two families of satellite repeats, VicTR-B of Vicia sativa and PisTR-B of Pisum sativum. The technique allowed FISH to be performed on mitotic chromosomes in a strand-specific manner, resulting in visualization of the repeat orientation along the chromosomes and with respect to the direction of telomeric repeats. The VicTR-B probe applied to V. sativa chromosomes produced signals on a single chromatid at most regions containing corresponding sequences, thus confirming a presence of long arrays of head-to-tail arranged repeat monomers which is typical for satellite DNA. However, hybridization signals of different or equal intensities on both chromatids were also detected at some loci, suggesting a more complex arrangement of the repeats. Similar observations were made for PisTR-B repeats on P. sativum chromosomes, although the proportion of loci displaying signals on both chromatids was lower. In contrast to VicTR-B, orientation of the PisTR-B clusters with respect to telomeric sequences appeared to be conserved among subtelomeric regions of metacentric chromosomes and of the short arms of acrocentric chromosomes.

Institute of Plant Molecular Biology Laboratory of Molecular Cytogenetics Ceské Budejovice Czech Republic

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Repetitive DNA in the pea (Pisum sativum L.) genome: comprehensive characterization using 454 sequencing and comparison to soybean and Medicago truncatula

Sequence homogenization and chromosomal localization of VicTR-B satellites differ between closely related Vicia species