A new insight on the evolution of polyploid Aegilops species from the complex Crassa: molecular-cytogenetic analysis

Abstract

Evolution of polyploid Aegilops species constituting complex Crassa was studied using C-banding and fluorescence in situ hybridization (FISH) with ten DNA probes. Genetic classification of nine of 14 chromosomes was suggested based on hybridization patterns of the D-genome specific repeats and distribution of rDNA loci; homoeologous groups and genome affinity of five chromosomes remain unknown. Correspondence between C-banding and FISH patterns of the repetitive DNAs was established with the aid of GAAn probe. We confirmed that the D1 genome of Ae. crassa (2n = 4x = 28, D1D1XcrXcr) was contributed by Ae. tauschii, although the retention of minor NORs on chromosomes 1D1 and 6D1 indicated that Ae. crassa probably emerged prior to the loss of the respective loci in the diploid progenitor. The Xcr genome might originate from the ancestral S*-genome species of Emarginata group. Genomes of Ae. crassa (4x) were significantly modified during speciation. The translocation Acr-6Xcr (T1) was identified in one tetraploid and all hexaploid Ae. crassa accessions and in Ae. vavilovii. Aegilops crassa (6x) also possessed the species-specific translocation 4D1-Fcr. Aegilops vavilovii originated from hybridization of Ae. crassa (4x) with Ae. searsii and was characterized by high translocation polymorphism. Two karyotypic groups: juv-I and juv-II were identified in Ae. juvenalis. All genomes of juv-I were significantly modified, whereas juv-II was karyotypically similar to Ae. crassa (4x) and Ae. umbellulata. Probably, juv-II originated independently of juv-I, from more recent hybridization of the same parental species.