Abstract
It has been known for decades that centromere size varies across species, but the factors involved in setting centromere boundaries are unknown. As a means to address this question, we estimated centromere sizes in ten species of the grass family including rice, maize, and wheat, which diverged 60~80 million years ago and vary by 40-fold in genome size. Measurements were made using a broadly reactive antibody to rice centromeric histone H3 (CENH3). In species-wide comparisons, we found a clear linear relationship between total centromere size and genome size. Species with large genomes and few chromosomes tend to have the largest centromeres (e.g., rye) while species with small genomes and many chromosomes have the smallest centromeres (e.g., rice). However, within a species, centromere size is surprisingly uniform. We present evidence from three oat–maize addition lines that support this claim, indicating that each of three maize centromeres propagated in oat are not measurably different from each other. In the context of previously published data, our results suggest that the apparent correlation between chromosome and centromere size is incidental to a larger trend that reflects genome size. Centromere size may be determined by a limiting component mechanism similar to that described for Caenorhabditis elegans centrosomes.Electronic supplementary materialThe online version of this article (doi:10.1007/s10577-012-9284-1) contains supplementary material, which is available to authorized users.
Highlights
Centromeres are the chromosomal domains responsible for accurate chromosome segregation during mitosis and meiosis
In the context of previously published data, our results suggest that the apparent correlation between chromosome and centromere size is incidental to a larger trend that reflects genome size
Centromeres are characterized by long segments of tandem repeats. These arrays extend several megabases in plants and animals, only a fraction of the repetitive sequences are incorporated into centromeric chromatin, which is specified by the specialized histone H3 variant centromeric histone H3 (CENH3) (Blower et al 2002; Zhong et al 2002)
Summary
Centromeres are the chromosomal domains responsible for accurate chromosome segregation during mitosis and meiosis. Centromeres are characterized by long segments of tandem repeats. These arrays extend several megabases in plants and animals, only a fraction of the repetitive sequences are incorporated into centromeric chromatin, which is specified by the specialized histone H3 variant CENH3 (Blower et al 2002; Zhong et al 2002). Fission yeast centromeres have two to three CENH3 nucleosomes and interact with two to four microtubules (Joglekar et al 2008). It is unlikely that this simple stoichiometric relationship can be applied to large genome species such as human, where there appears to be thousands of CENH3 nucleosomes in each centromere (Black et al 2007) but only ~17 microtubules per kinetochore (McEwen et al 2001)
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