Karyotype analysis of four Vicia species using in situ hybridization with repetitive sequences

Abstract

Mitotic chromosomes of four Vicia species (V. sativa, V. grandiflora, V. pannonica and V. narbonensis) were subjected to in situ hybridization with probes derived from conserved plant repetitive DNA sequences (18S-25S and 5S rDNA, telomeres) and genus-specific satellite repeats (VicTR-A and VicTR-B). Numbers and positions of hybridization signals provided cytogenetic landmarks suitable for unambiguous identification of all chromosomes, and establishment of the karyotypes. The VicTR-A and -B sequences, in particular, produced highly informative banding patterns that alone were sufficient for discrimination of all chromosomes. However, these patterns were not conserved among species and thus could not be employed for identification of homologous chromosomes. This fact, together with observed variations in positions and numbers of rDNA loci, suggests considerable divergence between karyotypes of the species studied.

Fig. 1. Localization of repetitive sequences on metaphase chromosomes of Vicia sativa (A, B), V. grandiflora (C–E), V. pannonica (F–H) and V. narbonensis (I–L). 5S rDNA (A) and VicTR‐B (B) sequences on V. sativa chromosomes. VicTR‐B (red) and 18S–25S rDNA (green) (C), 5S rDNA (D), and telomeric probes (E) on V. grandiflora. 18S–25S rDNA (F), VicTR‐A (red) and 5S rDNA (green) (G), and telomeric sequences (H) on V. pannonica. VicTR‐B (red) and 18S–25S rDNA (green) (I), VicTR‐B (red) and 5S rDNA (green) (J), VicTR‐A (red) and VicTR‐B (green) (K), and telomeric repeats (L) on V. narbonensis chromosomes. Sequences were localized using FISH except for VicTR repeats in B, C and G, which were visualized using PRINS. Chromosomes were counterstained with DAPI (blue). Bar = 10 µm.

Fig. 2. Idiograms of Vicia sativa (A), V. grandiflora (B), V. pannonica (C) and V. narbonensis (D). Presence and distribution of 18S–25S rRNA genes (orange), 5S rRNA genes (yellow), VicTR‐A (red), VicTR‐B (green) and telomeres (white) is indicated.

Fig. 3. Schematic comparison of chromosome sizes among Vicia sativa (A), V. grandiflora (B), V. pannonica (C) and V. narbonensis (D). Relative chromosome lengths were derived from the data in Table 2 and scaled according to the nuclear DNA content of the species (Table 1).