Absence of positive selection on CenH3 in Luzula suggests that holokinetic chromosomes may suppress centromere drive

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Authors

ZEDEK František BUREŠ Petr

Year of publication 2016
Type Article in Periodical
Magazine / Source Annals of Botany
MU Faculty or unit

Faculty of Science

Citation
Web http://aob.oxfordjournals.org/content/118/7/1347.abstract
Doi http://dx.doi.org/10.1093/aob/mcw186
Field Botany
Keywords centromere drive; meiotic drive; holokinetic chromosomes; holocentric chromosomes; positive selection; adaptive evolution; Centromeric histone H3; CenH3; CENP-A; holokinetic drive
Description Background and Aims: The centromere drive theory explains diversity of eukaryotic centromeres as a consequence of the recurrent conflict between centromeric repeats and centromeric histone H3 (CenH3), in which selfish centromeres exploit meiotic asymmetry and CenH3 evolves adaptively to counterbalance deleterious consequences of driving centromeres. Accordingly, adaptively evolving CenH3 has so far been observed only in eukaryotes with asymmetric meiosis. However, if such evolution is a consequence of centromere drive, it should depend not only on meiotic asymmetry but also on monocentric or holokinetic chromosomal structure. Selective pressures acting on CenH3 have never been investigated in organisms with holokinetic meiosis despite the fact that holokinetic chromosomes have been hypothesized to suppress centromere drive. Therefore, the present study evaluates selective pressures acting on the CenH3 gene in holokinetic organisms for the first time, specifically in the representatives of the plant genus Luzula (Juncaceae), in which the kinetochore formation is not co-localized with any type of centromeric repeat. Methods: PCR, cloning and sequencing, and database searches were used to obtain coding CenH3 sequences from Luzula species. Codon substitution models were employed to infer selective regimes acting on CenH3 in Luzula. Key Results: In addition to the two previously published CenH3 sequences from L. nivea, 16 new CenH3 sequences have been isolated from 12 Luzula species. Two CenH3 isoforms in Luzula that originated by a duplication event prior to the divergence of analysed species were found. No signs of positive selection acting on CenH3 in Luzula were detected. Instead, evidence was found that selection on CenH3 of Luzula might have been relaxed. Conclusions: The results indicate that holokinetism itself may suppress centromere drive and, therefore, holokinetic chromosomes might have evolved as a defence against centromere drive.
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