SORTING INDIVIDUAL CHROMOSOMES OF MAIZE

University of Nebraska-Lincoln, Center for Biotechnology, N322, George W. Beadle Center, Lincoln, NE 68588-0665 USA

The major research focus of our laboratory is the isolation and sorting individual chromosomes of important plant species. Sorted chromosomes have numerous important uses for plant genome research. These include production of chromosome or chromosome-region specific libraries, development of chromosome painting probes, study of chromosome architecture, and physical genome mapping. Our long-term goal is to purify each of the ten maize chromosomes, chromosome arms, and part of chromosome arms by taking advantage of the diversity of flow karyotypes generated from cytogenetic stocks and lines of maize, and available oat-maize addition lines. Use of addition line for maize chromosome sorting is a very exciting approach which has substantial promise in genome analysis. Hamster-human cell lines have been successfully exploited for human genome research (Van Dilla et al. 1986), and this is potentially an analogous system in plants. Fertile disomic additions (2n=42+2) are now available for maize chromosomes 2, 3, 4, 6, 7, and 9 (Riera-Lizarazu et al. 1996). An individual maize chromosome present in a genome with oat should be readily separatable from the oat chromosome by flow sorting based on relative chromosome size. All maize chromosomes are smaller than all oat chromosomes except the smallest one. We have tested this approach using oat-maize chromosome 9 addition line. Large numbers of mitotic metaphase chromosomes were successfully isolated from synchronized root tips of oat-maize chromosome 9 addition line and its parental oat (starter-1) and maize (Seneca 60) lines. As expected a peak (maize chromosome 9)well separated from the peaks for oat chromosomes and chromatids was seen. Large number of maize Chromosome 9 were collected with high purity by flow-sorting based on this peak. Sorting of pure chromosome 9 is not possible with use of normal maize lines.