Genetic relationship and genomic in situ hybridization analysis of the three genomes in Triticum aestivum

Common wheat (Triticum aestivum L.) is an allohexaploid, consisting of three different genomes (A(u), B and D) which are genetically closely related. Genomic DNA of the three possible genome donors, T. urartu Thum., Aegilops speltoides Tausch and Ae. tauschii Coss., were employed as probes to hybridize with the diploid genomic DNA digested by EcoR I and HindIII respectively. Both the hybridization strength and band patterns among the genomes would be good indicators of genome relationships. Combining distribution data of some repetitive DNA sequences cloned from T. urartu in the three genomes, the authors draw a conclusion that A(u) and D are more closely related to each other than either one to the B genome. Genomic in situ hybridization (GISH) of T. aestivum cv. Chinese Spring with genomic DNA probes of the three diploid progenitors respectively indicated that the three genomes could be discriminated clearly via GISH. The signals on the chromosomes of A(u) and D genomes were even. However, when Ae. speltoides DNA was used as probe, there were very strong cross hybridization and the signals condensed on some areas of the metaphasic chromosomes. In the interphase nucleus, the chromatin of B genome dispersed on the same region and the signals on the homologous chromosomes distributed symmetrically. Rich repetitive DNA sequences in B genome, especially the tandem repetitives, perhaps take an important role for the formation of the special hybridization pattern. The main difference between B and the other two genomes probably is in the repetitive DNA sequences.