Molecular-cytogenetic analysis of Aegilops triuncialis and identification of its chromosomes in the background of wheat

Abstract

Background: Species belonging to the genus Aegilops L. are an important source of genetic material for expanding genetic variability of wheat. Ae. triuncialis is an allotetraploid in this genus which was originated from hybridization of Ae. umbellulata and Ae. markgrafii (Greuter) Hammer. Although the Ae. triuncialis karyotype was thoroughly examined by conventional chromosome staining and Giemsa C-banding, it is still poorly characterized using FISH markers. The objective of this study was to test the fluorescence in situ hybridization (FISH) patterns of Ae. triuncialis (2n = 4x = 28, C(t)C(t)U(t)U(t)) chromosomes using different repetitive sequences and to compare the produced patterns to the chromosomes of its diploid ancestors, with the aim of establishing a generalized Ae. triuncialis idiogram and detection of Aegilops chromosomes in the background of wheat.

Results: The probes pSc119.2-1, pTa535-1, pAs1-1, (CTT)10 and the 45S rDNA clone from wheat (pTa71) were hybridized to chromosomes of Ae. triuncialis and compared with its diploid progenitors (Ae. umbellulata Zhuk., 2n = 2x = 14, UU and Ae. markgrafii (Greuter) Hammer, 2n = 2x = 14, CC) and Ae. cylindrica Host. (2n = 4x = 28, D(c)D(c)C(c)C(c)), another tetraploid species containing the C-genome. Ae. cylindrica was further analyzed by genomic in situ hybridization (GISH) using C genome probe in order to identify any possible translocation.

Conclusions: In general, FISH patterns of the U(t)- and C(t)-genome chromosomes of Ae. triuncialis were similar to those of U- and C-genome chromosomes of the diploid progenitor species Ae. umbellulata and Ae. markgrafii respectively, although some differences were observed. Two major 45S rDNA loci were revealed in the short arm of chromosomes A and C, of the C(t) genome which correspond to homoeologous groups 1 and 5 respectively. Minor 45S rDNA loci were mapped on the short arm of chromosomes 1U(t) and 5U(t). GISH analysis revealed three different non-reciprocal homologous or heterologous translocations between C(c) and D(c) chromosomes in all studied accessions of Ae. cylindrica.

Keywords: Aegilops triuncialis; Allopolyploidization; Chromosome marker; Evolution; Wheat–Aegilops triuncialis hybrid.

Figure 1

Representative karyotypes of Ae. umbellulata (accession S234), Ae. markgrafii (accession AE1418), Ae. triuncialis (accession S197) and Ae. cylindrica after FISH with different repetitive DNA probes. The yellow signals on Ae. triuncialis chromosomes represent 45S rDNA with the sizes relevant to the intensity of produced signals. The probe combination on each genome chromosomes is presented at the bottom of the figure with the related colour.

Figure 2

FISH and GISH patterns of Ae. triuncialis , Ae. cylindrica and F ₁ hybrids derived from wheat and Ae. triuncialis crosses. A: FISH signals from oligonucleotide probes pAS1-1 (FAM 5′ labeled), pSc119.2-1 (Tamra labelled) on the Ae. triuncialis (accession S197); B: Re-probing on the same preparation using Ae. markgrafii genomic DNA (red signals) and pTa71 clone (green signals); C: FISH signals from oligonucleotide probes pSc119.2-1 (FAM 5′ labeled), pTa535-1 (Tamra labelled) and (CTT)₁₀ (Cy3 labelled) on the Ae. cylindrica ecotype. Just signals of (CTT)₁₀ (mainly on C^c chromosomes) and pSc119.2-1 are presented in this picture. Using Texas Red filter, pTa535-1 signal was observed and identified D^c chromosomes which are presented in Figure 1; D: Re-probing on the same preparation using Ae. markgrafii genomic DNA (red signals) and pTa71 clone (green signals) which shows unbalanced translocation on chromosome pair 1D and 3C. The translocation on 3C is heterologous; E: FISH pattern of repetitive oligonucleotide probes pSc119.2-1 (FAM 5′ labelled), pTa535-1 (Tamra labelled) on mitotic metaphase chromosomes of a derived F₁ hybrid T. aestivum cv ‘Zarin’- Ae. triuncialis (accession S101); F: FISH pattern of repetitive oligonucleotide probes pSc119.2-1 (FAM 5′ labelled) and (CTT)₁₀ (Cy3 labelled) on mitotic metaphase chromosomes of a derived F₁ hybrid T. aestivum cv ‘Pishgam’- Ae. triuncialis (accession S101). Bar = 10 μm.