Abstract
The precise assembly of the kinetochore complex at the centromere is epigenetically determined by substituting histone H3 with the centromere-specific histone H3 variant CENH3 in centromeric nucleosomes. A chromosome 1B reconstructed in wheat by centric misdivision from two wheat-rye centric translocations is known to carry a hybrid wheat-rye centromere. The resulting hybrid (dicentric)centromere is composed of both wheat and rye centromeric repeats. As CENH3 is a marker for centromere activity, we applied Immuno-FISH followed by ultrastructural super-resolution microscopy to address whether both or only parts of the hybrid centromere are active. Our study demonstrates that only the rye-derived centromere part incorporates CENH3 of wheat in the 1BL/1RS hybrid centromere. This finding supports the notion that one centromere part of a translocated chromosome undergoes inactivation, creating functional monocentric chromosomes to maintain chromosome stability.
Highlights
The centromere is the assembly site for the proteinaceous kinetochore complex, which enables the proper segregation of sister chromatids and their transmission to the daughter cells during mitosis and meiosis
As CENH3 is a mark for centromere activity (Talbert and Henikoff, 2020), the hybrid 1BL/1RS centromere activity was determined by immunostaining using antibodies that crossreacts with the CENH3 proteins of cereals (Nagaki et al, 2004; Liu et al, 2008; Houben et al, 2011)
In all analyzed dividing cells of five plants, CENH3 signals consistently co-localized with the wheat centromeric repeat CRW2 in all non-translocation chromosomes
Summary
The centromere is the assembly site for the proteinaceous kinetochore complex, which enables the proper segregation of sister chromatids and their transmission to the daughter cells during mitosis and meiosis. Despite the conserved function of the centromere, the primary constriction of monocentric species is generally enriched in highly diverged gene-free repetitive sequences. These repeats include satellite DNAs and retrotransposons (Barra and Fachinetti, 2018; Talbert and Henikoff, 2020). Various 1BL/1RS translocations have served as valuable stocks in wheat breeding programs as chromosome 1R contains insect and disease resistance genes (Kim et al, 2004)1 To address whether both or only one part of the 1BL/1RS hybrid centromere is active Wang et al (2017) applied a combination of immuno-FISH, chromatin immunoprecipitation (ChIP)-qPCR, and RT-PCR. Our findings demonstrate that only the rye-derived centromere incorporates CENH3 of wheat into the hybrid centromere of 1BL/1RS
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