|Vales, M. Isabel|
Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2007
Publication Date: 1/22/2008
Citation: Okagaki, R.J., Jacobs, M.S., Stec, A.O., Kynast, R.G., Buescher, E., Rines, H.W., Vales, M., Riera-Lizarazu, O., Schneerman, M., Doyle, G., Friedman, K.L., Staub, R.W., Weber, D.F., Kamps, T.L., Amarillo, I.F., Chase, C.D., Bass, H.W., Phillips, R.L. 2008. Maize centromere mapping: A comparison of physical and genetic strategies. Journal of Heredity. 99:85-93. Interpretive Summary: In plants, as in other higher organisms, the genetic material or DNA within each cell is organized into structures termed chromosomes. These structures can be seen under a microscope serving to separate duplicating copies of the DNA into the daughter cells during cell division. Along each of these chromosomes is a region termed a centromere, which serves as an anchor point for the cellular mechanics that separate the chromosomes during cell division. Relating the physical position of these centromeres to the organization of the genes detected by molecular analysis and genetic recombination in corn has been elusive for geneticists studying mechanisms of inheritance toward genetic improvement of our most important crop. We have combined information from several different techniques to determine the positions of the centromeres in relation to the order of genes along corn chromosomes. One primary technique involved the use of novel materials we have developed in which segments of corn chromosomes have been incorporated into the genetic materials of another cereal grass, oat. Instances of co-integration of molecularly detected corn genes and centromeres reveal their physical positions relative to one another. Results using this and other techniques were consistent for four of the chromosomes studied, but variation in relative centromere position was found for three other chromosomes. The variation was attributed to differences among the corn lines analyzed in this genetically highly variable species. This information is useful to other scientists trying to understand the organization of the genetic material of corn and other species to enable genetic manipulation for crop improvement.
Technical Abstract: The location of chromosome centromeres in various maize genetic maps relative to physical maps has not been consistently and clearly identified due to the paucity of markers and low recombination in the highly heterochromatic centromeric and flanking regions. Centromere positions on seven maize chromosomes were compared on the basis of data from four to six techniques per chromosome. Centromere positions were first located relative to molecular markers by means of radiation-hybrid lines and centric-fission lines recovered from oat-maize chromosome-addition lines. These centromere positions were then compared with new data from centric-fission lines recovered from maize plants, half-tetrad mapping, and fluorescence in-situ hybridizations and to data from earlier studies. Surprisingly, the choice of mapping technique made little difference. On four chromosomes, 2, 4, 9, and 10, all techniques consistently located the centromere within a small interval. Centromere positions on chromosomes 1, 3, and 6 were not consistent even in studies using the same technique. The conflicting centromere map positions on chromosomes 1, 3, and 6 could be explained by pericentric inversions or alternative centromere positions on these chromosomes.