title: B chromosomes of rye are highly conserved and accompanied the development of early agriculture.
abstract: OBJECTIVE
  Supernumerary B chromosomes (Bs) represent a specific type of selfish genetic element. As Bs are dispensable for normal growth, it is expected to observe B polymorphisms among populations. To address whether Bs maintained in geographically distinct populations of cultivated and weedy rye are polymorphic, the distribution patterns and the transcriptional activity of different B-located repeats were analysed.
  
  
  METHODS
  Bs of cultivated and weedy rye from seven origins were analysed by fluorescence in situ hybridization (FISH) with probes specific for the pericentromeric and interstitial regions as well as the B-specific non-disjunction control region. The DNA replication, chromatin composition and transcription behaviour of the non-disjunction regions were determined. To address whether the B-marker repeats E3900 and D1100 have diverged genotypes of different origin at the sequence level, the genomic sequences of both repeats were compared between cultivated rye and weedy rye from five different origins.
  
  
  RESULTS
  B chromosomes in cultivated and weedy rye have maintained a similar molecular structure at the level of subspecies. The high degree of conservation of the non-disjunction control region regarding its transcription activity, histone composition and replication underlines the functional importance of this chromosome region for the maintenance of Bs. The conserved chromosome structure suggests a monophyletic origin of the rye B. As Bs were found in different countries, it is likely that Bs were frequently present in the seed material used in early agriculture.
  
  
  CONCLUSIONS
  The surprisingly conserved chromosome structure suggests that although the rye Bs experienced rapid evolution including multiple rearrangements at the early evolutionary stages, this process has slowed significantly and may have even ceased during its recent evolution.
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr. 3, D-06466 Gatersleben, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Marques
authors.forename: Ali M
authors.initials: AM
authors.lastname: Banaei-Moghaddam
authors.forename: Sonja
authors.initials: S
authors.lastname: Klemme
authors.forename: Frank R
authors.initials: FR
authors.lastname: Blattner
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Niwa
authors.forename: Marcelo
authors.initials: M
authors.lastname: Guerra
authors.forename: Andreas
authors.initials: A
authors.lastname: Houben
mesh_terms: D001483:Base Sequence; D032461:Chromosomes, Plant; D017124:Conserved Sequence; D018556:Crops, Agricultural / Q000235:genetics*; D019143:Evolution, Molecular; D018745:Genome, Plant; D017404:In Situ Hybridization, Fluorescence; D009630:Nondisjunction, Genetic; D012434:Secale / Q000235:genetics*
keywords: Secale cereale; chromosomal evolution; chromosomal polymorphisms; genome evolution; non-disjunction control; parasitic chromosome; rye