Review: The cytogenetic and molecular architecture of chromosome 1R—one of the most widely utilized sources of alien chromatin in wheat varieties

Conclusions

The evolution of chromosome 1R has resulted in a structure with genes that are similar enough, qualitatively and quantitatively, to those in wheat to allow substitution for wheat chromosomes. The sequences dispersed between the genes, and those arranged tandemly in large blocks, have however undergone major quantitative changes (and possibly qualitative changes as well). Amplification events since the time that wheat and rye have been separated in an evolutionary sense have generated arrays of repetitive sequence families that characterize the rye chromosomes (including 1R) and distinguish them from wheat chromosomes. The genetic mapping of chromosome 1R at the level of DNA has provided a range of probes for the study of 1R chromosome segments as they are manipulated in commercial wheat cultivars.

The extensive utilization of chromosome 1R as a source of disease resistance genes in wheat implies that rye genes are normally expressed in a wheat background. This is, however, not always the case and a particularly well studied example is the suppression of rRNA gene expression (reviewed in Applels et al. 1986a). These isolated examples of modified expression of rye genes in a wheat background are presumably the result of evolutionary change in the rye promoter regions resulting in their reduced competitiveness when combined with wheat genes in a common cytoplasmic environment. The cytoplasm of wheat plants carrying rye chromosome fragments would be dominated by protein molecules adapted to wheat promoters.