Chromosome arrangement and nuclear architecture but not centromeric sequences are conserved between Arabidopsis thaliana and Arabidopsis lyrata.

In contrast to the situation described for mammals and Drosophila, chromosome territory (CT) arrangement and somatic homologous pairing in interphase nuclei of Arabidopsis thaliana (n = 5) are predominantly random except for a more frequent association of the chromosomes bearing a homologous nucleolus organizer region. To find out whether this chromosome arrangement is also characteristic for other species of the genus Arabidopsis, we investigated Arabidopsis lyrata ssp. lyrata (n = 8), one of the closest relatives of A. thaliana. First, we determined the size of each chromosome and chromosome arm, the sequence type of centromeric repeats and their distribution between individual centromeres and the position of the 5S/45S rDNA arrays in A. lyrata. Then we demonstrated that CT arrangement, homologous pairing and sister chromatid alignment of distinct euchromatic and/or heterochromatic regions within A. lyrata interphase nuclei are similar to that in A. thaliana nuclei. Thus, the arrangement of interphase chromosomes appears to be conserved between both taxa that diverged about 5 million years ago. Since the chromosomes of A. lyrata resemble those of the presumed ancestral karyotype, a similar arrangement of interphase chromosomes is also to be expected for other closely related diploid species of the Brassicaceae family.