Karyotype reshufflings of Festuca pratensis × Lolium perenne hybrids

Abstract

Many different processes have an impact on the shape of plant karyotype. Recently, cytogenetic examination of Lolium species has revealed the occurrence of spontaneous fragile sites (FSs) associated with 35S rDNA regions. The FSs are defined as the chromosomal regions that are sensitive to forming gaps or breaks on chromosomes. The shape of karyotype can also be determined by interstitial telomeric sequences (ITSs), what was recognized for the first time in this paper in chromosomes of Festuca pratensis × Lolium perenne hybrids. Both FSs and ITSs can contribute to genome instabilities and chromosome rearrangements. To evaluate whether these cytogenetic phenomena have an impact on karyotype reshuffling observed in Festuca × Lolium hybrids, we examined F₁ F. pratensis × L. perenne plants and generated F₂-F₉ progeny by fluorescent in situ hybridization (FISH) using rDNA sequences, telomere and centromere probes, as well as by genomic in situ hybridization (GISH). Analyses using a combination of FISH and GISH revealed that intergenomic rearrangements did not correspond to FSs but overlapped with ITSs for several analyzed genotypes. It suggests that internal telomeric repeats can affect the shape of F. pratensis × L. perenne karyotypes. However, other factors that are involved in rearrangements and have a more crucial impact could exist, but they are still unknown.

Keywords: Festuca pratensis × Lolium perenne hybrids; Fragile sites; Genetic instability; Interstitial telomeric sequences; Karyotype reshuffling.

Fig. 1

FISH mapping of clone 395 (yellow) to F. pratensis and L. perenne chromosomes. a Diploid (2n = 14) F. pratensis. b Tetraploid (2n = 28) F. pratensis. c Diploid (2n = 14) L. perenne. d Tetraploid (2n = 28) L. perenne. The clone was labeled with Atto647 fluorochrome; chromosomes were counterstained with DAPI (blue)

Fig. 2

The types and frequency of rearrangements occurring in rDNA-bearing chromosomes for F. pratensis × L. perenne hybrids. Yellow lines show the position of centromeric regions; purple lines show the position of 35S rDNA; red lines show the position of 5S rDNA; white dotted lines show the position of rearrangements (R)

Fig. 3

The interstitial telomeric sequences in F. pratensis × L. perenne hybrids: a Genotype F₄-15—lack of colocalization of ITSs (yellow arrows) with centromeric sequences, rDNA loci, and GISH. b Genotype F₇-40—colocalization of ITSs (yellow arrows) with location of rearrangements in L. perenne chromosomes and two additional ITSs (white arrows) in F. pratensis chromosomes. c Genotype F₈-21—colocalization of ITSs (yellow arrows) with centromeric and pericentromeric regions in F. pratensis chromosomes and two additional ITSs (white arrows) in interstitial regions of F. pratensis chromosomes. In each panel, from the left to right side: telomeric repeats (red), centromeric sequence (yellow), 5S and 35S rDNA sequences (red and green, respectively), and GISH results were presented

Fig. 4

Metaphase of F. pratensis × L. perenne hybrid plant (F₇-47) with fragile sites associated with 35S rDNA: a DAPI staining. b 35S rDNA-FISH (green) (the white dotted lines link broken chromosome parts). c Centromeric clone 395. d GISH