Non-Rabl chromosome organization in endoreduplicated nuclei of barley embryo and endosperm tissues

Rabl organization is a type of interphase chromosome arrangement with centromeres and telomeres clustering at opposite nuclear poles. Here, we analyzed nuclear morphology and chromosome organization in cycling and endoreduplicated nuclei isolated from embryo and endosperm tissues of developing barley seeds. We show that endoreduplicated nuclei have an irregular shape, less sister chromatid cohesion at 5S rDNA loci, and a reduced amount of centromeric histone CENH3. While the chromosomes of the embryo and endosperm nuclei are initially organized in Rabl configuration, the centromeres and telomeres are intermingled within the nuclear space in the endoreduplicated nuclei with an increasing endoreduplication level. Such a loss of chromosome organization suggests that Rabl configuration is introduced and further reinforced by mitotic divisions in barley cell nuclei in a tissue- and seed age-dependent manner. Endoreduplication leads to loss of Rabl organization in barley embryo and endosperm nuclei, and suggests mitosis as the major factor reinforcing this prominent chromosome configuration.

Automated summary

In this study, the nuclear morphology and chromosome organization in cycling and endoreduplicated nuclei of barley seeds were analyzed. It was found that endoreduplicated nuclei have an irregular shape, reduced sister chromatid cohesion, and decreased centromeric histone CENH3. While the chromosomes initially have a Rabl configuration, the organization is lost and intermingled in endoreduplicated nuclei with increasing endoreduplication. This suggests that mitotic divisions play a role in introducing and reinforcing Rabl configuration in a tissue- and seed age-dependent manner.