Abstract
We observed the formation of chromatin ring structures at centromeres of somatic rye and Arabidopsis chromosomes. To test whether this behavior is present also in other plant species and tissues we analyzed Arabidopsis, rye, wheat, Aegilops and barley centromeres during cell divisions and in interphase nuclei by immunostaining and FISH. Furthermore, structured illumination microscopy (super-resolution) was applied to investigate the ultrastructure of centromere chromatin beyond the classical refraction limit of light. It became obvious, that a ring formation at centromeres may appear during mitosis, meiosis and in interphase nuclei in all species analyzed. However, varying centromere structures, as ring formations or globular organized chromatin fibers, were identified in different tissues of one and the same species. In addition, we found that a chromatin ring formation may also be caused by subtelomeric repeats in barley. Thus, we conclude that the formation of chromatin rings may appear in different plant species and tissues, but that it is not specific for centromere function. Based on our findings we established a model describing the ultrastructure of plant centromeres and discuss it in comparison to previous models proposed for animals and plants.
Highlights
Centromeres of eukaryotic chromosomes are regions where spindle fibers attach to perform chromatid or homolog separation during mitosis and meiosis
Applying super-resolution microscopy we investigated the ultrastructure of centromere chromatin
We found that in different monocot plants and the eudicot species A. thaliana centromeric chromatin fibers may establish globular and/or pad-like structures
Summary
Centromeres of eukaryotic chromosomes are regions where spindle fibers attach to perform chromatid or homolog separation during mitosis and meiosis. Different types of centromeres exist (Cuacos et al, 2015). They represent a distinct single primary constriction (monocentric chromosomes). They may be undiscernible (no primary constriction at very small chromosomes), as e.g., described in Giardia intestinalis Kofoid and Christiansen 1915 (Tumová et al, 2015). Primary constrictions can be elongated to several microns (polycentric chromosomes) as found e.g., in wallaby hybrids (Metcalfe et al, 2007), Lathyrus and pea (Neumann et al, 2012, 2016), or form a groove along both sister chromatids of holocentric chromosomes, e.g., of the wood rush Luzula elegans LOWE (Heckmann et al, 2011; Wanner et al, 2015).
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