Genome Evolution in Allopolyploid Wheats: Evidence from Low Copy DNA Sequences

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9508686 Talbert Many plant species, and some animal species as well, have originated following hybridization between two or more progenitor species. In many cases, both sets of chromosomes in each of the parental (diploid) species are retained in the hybrid, which thus becomes a tetra(allopoly)ploid organism. Many of our common crop plants like wheat, oats, cotton, and tobacco are allopolyploids. The evolution of these species may proceed along pathways that are not open to diploid species. For instance, it has been suggested that allopolyploids are buffered against deleterious mutations more effectively than diploids. One complication in tracing the ancestry of polyploid plant species, however, lies in the finding that some diploid species are themselves hybrid derivatives of past crossings. It is for this reason that polyploid hybrids can be hypothesized to combine multiple parental lines. Drs. Luther Talbert and Matthew Lavin of Montana State University are making imaginative use of new methods of DNA analysis to study the origins of polyploid wheats, and in particular the group designated as 'B' genome wheats. Their work builds upon three converging research enterprises: 1) the development of specific markers of genes on the two arms of each chromosome in wheats; 2) the use of breeding stocks of polyploid wheats that lack a specific chromosome (so-called nullisomic lines); and 3) the search for and maintenance of wild diploid wheats collected in the Middle East. Their studies will test the hypothesis that each genome is actually a composite of chromosomes from several progenitor species, and if so, from which progenitors. The use of single or low copy-number nuclear DNA markers on chromosomes should prove adaptable to other plant systems, in helping to solve the problem of hybrid origins of polyploids.