Association between simple sequence repeat-rich chromosome regions and intergenomic translocation breakpoints in natural populations of allopolyploid wild wheats.

BACKGROUND AND AIMS Repetitive DNA sequences are thought to be involved in the formation of chromosomal rearrangements. The aim of this study was to analyse the distribution of microsatellite clusters in Aegilops biuncialis and Aegilops geniculata, and its relationship with the intergenomic translocations in these allotetraploid species, wild genetic resources for wheat improvement. METHODS The chromosomal localization of (ACG)(n) and (GAA)(n) microsatellite sequences in Ae. biuncialis and Ae. geniculata and in their diploid progenitors Aegilops comosa and Aegilops umbellulata was investigated by sequential in situ hybridization with simple sequence repeat (SSR) probes and repeated DNA probes (pSc119·2, Afa family and pTa71) and by dual-colour genomic in situ hybridization (GISH). Thirty-two Ae. biuncialis and 19 Ae. geniculata accessions were screened by GISH for intergenomic translocations, which were further characterized by fluorescence in situ hybridization and GISH. KEY RESULTS Single pericentromeric (ACG)(n) signals were localized on most U and on some M genome chromosomes, whereas strong pericentromeric and several intercalary and telomeric (GAA)(n) sites were observed on the Aegilops chromosomes. Three Ae. biuncialis accessions carried 7U(b)-7M(b) reciprocal translocations and one had a 7U(b)-1M(b) rearrangement, while two Ae. geniculata accessions carried 7U(g)-1M(g) or 5U(g)-5M(g) translocations. Conspicuous (ACG)(n) and/or (GAA)(n) clusters were located near the translocation breakpoints in eight of the ten translocated chromosomes analysed, SSR bands and breakpoints being statistically located at the same chromosomal site in six of them. CONCLUSIONS Intergenomic translocation breakpoints are frequently mapped to SSR-rich chromosomal regions in the allopolyploid species examined, suggesting that microsatellite repeated DNA sequences might facilitate the formation of those chromosomal rearrangements. The (ACG)(n) and (GAA)(n) SSR motifs serve as additional chromosome markers for the karyotypic analysis of UM genome Aegilops species.