Is the aneuploid chromosome in an apomictic Boechera holboellii a genuine B chromosome?

T.F. Sharbel, M.L. Voigt, T. Mitchell-Olds, L. Kantama, J.H.S.G.M. de Jong

Research output: Contribution to journalArticleAcademicpeer-review

41 Citations (Scopus)

Abstract

The Boechera holboellii complex comprises B. holboellii and B. drummondii, both of which can reproduce through sex or apomixis. Sexuality is associated with diploidy, whereas apomictic individuals can either be diploid, aneuploid or triploid. Aneuploid individuals are found in geographically and genetically distinct populations and contain a single extra chromosome. It is unknown whether the supernumerary chromosomes are shared by common descent (single origin) or have originated via introgressive hybridizations associated with the repeated transition from diploidy to triploidy. Diploid plants containing the extra chromosome(s) reproduce apomictically, suggesting that the supernumerary elements are associated with apomixis. In this study we compared flow cytometry data, chromosome morphology, and DNA sequences of sexual diploid and apomictic aneuploids in order to establish whether the extra chromosome fits the classical concept of a B chromosome. Karyotype analyses revealed that the supernumerary chromosome in the metaphase complement is heterochromatic and often smaller than the A chromosomes, and differs in length between apomictic plants from different populations. DNA sequence analyses furthermore demonstrated elevated levels of non-synonymous substitutions in one of the alleles, likely that on the aneuploid chromosome. Although the extra chromosome in apomictic Boechera does not go through normal reductional meiosis, in which it may get eliminated or accumulated by a B-chromosome-specific process, its variable size and heterochromatic nature does meet the remaining criteria for a genuine B chromosome in other species. Its prevalence and conserved genetic composition nonetheless implies that this chromosome, if truly a B, may be atypical with respect to its influence on its carriers. Copyright (C) 2004 S. Karger AG, Basel.
Original languageEnglish
Pages (from-to)173-183
JournalCytogenetic and Genome Research
Volume106
Issue number2-4
DOIs
Publication statusPublished - 2004

Keywords

  • arabis-holboellii
  • evolutionary genetics
  • molecular systematics
  • natural-populations
  • rust infection
  • brassicaceae
  • apomixis
  • arabidopsis
  • plants
  • parthenogenesis

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