Abstract
During interphase, the chromosomes of eukaryotes decondense and they occupy distinct regions of the nucleus, called chromosome domains or chromosome territories (CTs). In plants, the Rabl’s configuration, with telomeres at one pole of nucleus and centromeres at the other, appears to be common, at least in plants with large genomes. It is unclear whether individual chromosomes of plants adopt defined, genetically determined addresses within the nucleus, as is the case in mammals. In this study, the nuclear disposition of alien rye and barley chromosomes and chromosome arm introgressions into wheat while using 3D-FISH in various somatic tissues was analyzed. All of the introgressed chromosomes showed Rabl’s orientation, but their relative positions in the nuclei were less clear. While in most cases pairs of introgressed chromosomes occupied discrete positions, their association (proximity) along their entire lengths was rare, and partial association only marginally more frequent. This arrangement is relatively stable in various tissues and during various stages of the cell cycle. On the other hand, the length of a chromosome arm appears to play a role in its positioning in a nucleus: shorter chromosomes or chromosome arms tend to be located closer to the centre of the nucleus, while longer arms are more often positioned at the nuclear periphery.
Highlights
During interphase, eukaryotic chromosomes decondense and occupy distinct regions of the nucleus, named chromosome territories or chromosome domains [1,2]
Sengupta et al [27] provided evidence of the stable positioning of gene-poor human chromosomes 7 and 18 on the periphery of human × mouse hybrid nuclei. These results indicate that the location of a chromosome territories (CTs) in a hybrid nucleus might be affected more by its gene content rather than by its parental origin
Large chromosomes in species with large genomes, such as wheat, barley, and rye, assume the Rabl’s configuration, while species with small chromosomes and small genomes seem to display different organizations, such as the Rosette observed in Arabidopsis [17,29,38,39,40]
Summary
Eukaryotic chromosomes decondense and occupy distinct regions of the nucleus, named chromosome territories or chromosome domains [1,2]. Chromosome painting, where whole chromosome probes are used for FISH of single CTs or groups of CTs, showed that interphase chromosomes are radially arranged in human [7,8] primates [9], chicken [10], and mouse [5] This type of the CT arrangement appears to be evolutionary conserved among vertebrates [11,12]. In the Rabl’s orientation [13], centromeres are grouped at, or close to, the nuclear periphery at one pole of the nucleus, while telomeres are dispersed at the opposite pole [14] This configuration is found in many large-genome plant species and is a remnant of anaphase chromosome movement [15]. The position of CTs and the arrangement of heterochromatin domains is mostly random in differentiated as well as in meristematic tissues, except for chromosomes with nucleolar organizing regions (NORs), which associate with the nucleolus [16,19]
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