RAPID GENOMIC CHANGES IN NEWLY SYNTHESIZED AMPHIPLOIDS OF TRITICUM AND AEGILOPS - I - CHANGES IN LOW-COPY NONCODING DNA-SEQUENCES

We recently reported that allopolyploid formation in wheat was accompa nied by rapid nonrandom elimination of specific low-copy, noncoding DN A sequences. These sequences occur in all diploid progenitors but are chromosome- or genome-specific at the polyploid level. To further inve stigate this phenomenon, we studied nine of these sequences, six chrom osome-specific sequences and three genome-specific sequences, all isol ated from common wheat. The various sequences were hybridized to DNA d erived from nine newly synthesized amphiploids at different ploidy lev els and to DNA from their parental lines. Although sequences homologou s to the probes occur in all parental lines, a nonrandom loss of hybri dization fragments was found at a high frequency in all amphiploids st udied. In addition, a ''loss/gain'' of a hybridization fragment(s) was noticed in some of the amphiploids at lower frequency. Neither the ty pe nor the frequency of changes was affected by intergenomic recombina tion or DNA methylation. It is suggested that rapid genomic changes cu lminated in a ''programmed'' pattern of elimination and (or) modificat ion of specific low-copy DNA sequences following allopolyploidization. These events augmented the differentiation of homoeologous chromosome s, thus providing the physical basis for the diploid-like cytological behavior of polyploid wheat.