title: Naturally occurring differences in CENH3 affect chromosome segregation in zygotic mitosis of hybrids.
abstract: The point of attachment of spindle microtubules to metaphase chromosomes is known as the centromere. Plant and animal centromeres are epigenetically specified by a centromere-specific variant of Histone H3, CENH3 (a.k.a. CENP-A). Unlike canonical histones that are invariant, CENH3 proteins are accumulating substitutions at an accelerated rate. This diversification of CENH3 is a conundrum since its role as the key determinant of centromere identity remains a constant across species. Here, we ask whether naturally occurring divergence in CENH3 has functional consequences. We performed functional complementation assays on cenh3-1, a null mutation in Arabidopsis thaliana, using untagged CENH3s from increasingly distant relatives. Contrary to previous results using GFP-tagged CENH3, we find that the essential functions of CENH3 are conserved across a broad evolutionary landscape. CENH3 from a species as distant as the monocot Zea mays can functionally replace A. thaliana CENH3. Plants expressing variant CENH3s that are fertile when selfed show dramatic segregation errors when crossed to a wild-type individual. The progeny of this cross include hybrid diploids, aneuploids with novel genetic rearrangements and haploids that inherit only the genome of the wild-type parent. Importantly, it is always chromosomes from the plant expressing the divergent CENH3 that missegregate. Using chimeras, we show that it is divergence in the fast-evolving N-terminal tail of CENH3 that is causing segregation errors and genome elimination. Furthermore, we analyzed N-terminal tail sequences from plant CENH3s and discovered a modular pattern of sequence conservation. From this we hypothesize that while the essential functions of CENH3 are largely conserved, the N-terminal tail is evolving to adapt to lineage-specific centromeric constraints. Our results demonstrate that this lineage-specific evolution of CENH3 causes inviability and sterility of progeny in crosses, at the same time producing karyotypic variation. Thus, CENH3 evolution can contribute to postzygotic reproductive barriers.
authors.affiliation: Department of Plant Biology and Genome Center, University of California, Davis, Davis, California, United States of America.
authors.forename: Shamoni
authors.initials: S
authors.lastname: Maheshwari
authors.affiliation: Department of Plant Biology and Genome Center, University of California, Davis, Davis, California, United States of America.
authors.forename: Ek Han
authors.initials: EH
authors.lastname: Tan
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom.
authors.forename: Allan
authors.initials: A
authors.lastname: West
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom.
authors.forename: F Chris H
authors.initials: FC
authors.lastname: Franklin
authors.affiliation: Department of Plant Biology and Genome Center, University of California, Davis, Davis, California, United States of America.
authors.forename: Luca
authors.initials: L
authors.lastname: Comai
authors.affiliation: Department of Plant Biology, University of California, Davis, Davis, California, United States of America; Howard-Hughes Medical Institute and the Gordon and Betty Moore Foundation, University of California, Davis, Davis, California, United States of America.
authors.forename: Simon W L
authors.initials: SW
authors.lastname: Chan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D001324:Autoantigens / Q000235:genetics*; D005075:Biological Evolution; D002503:Centromere / Q000235:genetics; D000076247:Centromere Protein A; D002678:Chimera / Q000235:genetics; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics*; D020090:Chromosome Segregation / Q000235:genetics*; D004171:Diploidy; D006238:Haploidy; D006657:Histones / Q000235:genetics; D008938:Mitosis / Q000235:genetics*; D008969:Molecular Sequence Data; D015053:Zygote / Q000254:growth & development
chemical_list: D001324:Autoantigens; D000076247:Centromere Protein A; D002868:Chromosomal Proteins, Non-Histone; D006657:Histones