title: Karyotype evolution in apomictic Boechera and the origin of the aberrant chromosomes.
abstract: Chromosome rearrangements may result in both decrease and increase of chromosome numbers. Here we have used comparative chromosome painting (CCP) to reconstruct the pathways of descending and ascending dysploidy in the genus Boechera (tribe Boechereae, Brassicaceae). We describe the origin and structure of three Boechera genomes and establish the origin of the previously described aberrant Het and Del chromosomes found in Boechera apomicts with euploid (2n = 14) and aneuploid (2n = 15) chromosome number. CCP analysis allowed us to reconstruct the origin of seven chromosomes in sexual B. stricta and apomictic B. divaricarpa from the ancestral karyotype (n = 8) of Brassicaceae lineage I. Whereas three chromosomes (BS4, BS6, and BS7) retained their ancestral structure, five chromosomes were reshuffled by reciprocal translocations to form chromosomes BS1-BS3 and BS5. The reduction of the chromosome number (from x = 8 to x = 7) was accomplished through the inactivation of a paleocentromere on chromosome BS5. In apomictic 2n = 14 plants, CCP identifies the largely heterochromatic chromosome (Het) being one of the BS1 homologues with the expansion of pericentromeric heterochromatin. In apomictic B. polyantha (2n = 15), the Het has undergone a centric fission resulting in two smaller chromosomes - the submetacentric Het' and telocentric Del. Here we show that new chromosomes can be formed by a centric fission and can be fixed in populations due to the apomictic mode of reproduction.
authors: CEITEC - Central European Institute of Technology, Masaryk University, Brno, CZ-62500, Czech Republic.
authors: Terezie
authors: T
authors: Mandáková
authors: Plant Systematics Group, Wageningen University (WU), Droevendaalsesteeg 1, Wageningen, 6708 PB, The Netherlands.
authors: M Eric
authors: ME
authors: Schranz
authors: Apomixis Research Group, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, D-06466, Germany.
authors: Timothy F
authors: TF
authors: Sharbel
authors: Laboratory of Genetics, Wageningen UR PSG, P.O. Box 16, Wageningen, 6700 AA, The Netherlands.
authors: Hans
authors: H
authors: de Jong
authors: CEITEC - Central European Institute of Technology, Masaryk University, Brno, CZ-62500, Czech Republic.
authors: Martin A
authors: MA
authors: Lysak
mesh_terms: D000782:Aneuploidy; D019607:Brassicaceae / Q000235:genetics*; D002869:Chromosome Aberrations; D020223:Chromosome Painting / Q000379:methods*; D032461:Chromosomes, Plant; D019143:Evolution, Molecular; D018745:Genome, Plant; D059785:Karyotype
keywords: Boechera; Brassicaceae; apomixis; centromere inactivation; chromosome fission; heterochromatin; karyotype evolution