Plant & Animal Genome VI Conference

W81

COLLINEARITY BETWEEN THE GENOMES OF Arabidopsis thaliana AND Brassica SPECIES.

Agriculture and Agri-Food Canada, Molecular Genetics Section, Saskatoon Research Centre, 107 Science Place, Saskatoon, S7N 0X2

Comparative genome analysis can uncover the pattern of conservation of both precise gene order and gross karyotype. The international genome sequencing initiative for the model dicot Arabidopsis will lead to vast numbers of genes with defined physiological, biochemical and/or developmental roles being precisely localised on the simple Arabidopsis genome. We are studying collinearity between Arabidopsis and species of the Brassica genus to allow exploitation of this vast reservoir of knowledge by researchers and plant breeders working with crucifer crops. Our work has shown that single copy regions of Arabidopsis routinely detect six homologous copies distributed over the Brassica napus genome, three copies in each of the diploid ancestral genomes. Our data suggest that the diploid Brassica species have evolved through a common hexaploid ancestor which was formed by the fusion of three closely related genomes of similar size to that of modern day Arabidopsis. It is likely that all modern day crucifers will prove to be composed of equivalent genome complements and that the many variations in crucifer genome organisation have occurred chiefly though chromosome fusion and chromosome rearrangements. The collinearity of the genomes of Arabidopsis and Brassica will accelerate technology transfer between the model plant and important crops but only if the ramifications of gene duplication in polyploid Brassica species are appreciated. In a similar way, the extent of genome collinearity is not uniform and certain regions, particularly those in close proximity to centromeres, exhibit high densities of discontinuities in collinearity.