University of Minnesota and USDA-ARS

A radiation hybrid system for the genetic and physical mapping of the corn genome --Okagaki RJ, Kynast RG, Odland WE, Stec A, Russell CD, Zaia HA, Rines HW, Phillips RL Oat-maize chromosome addition lines can be generated by crossing oat with maize and rescuing the developing F1 embryos through in vitro culture. Approximately one-third of the plantlets retained one or more maize chromosomes added to the haploid oat genome. These plants provide the starting material for a project to develop a radiation hybrid system for mapping individual maize chromosomes. The major objectives for this project are:

1) Establish fertile disomic addition lines for each maize chromosome and supply seed and genomic DNA to the scientific community.

2) Produce low and high-resolution radiation hybrid maps.

3) Develop high-throughput technologies for mapping ESTs to chromosomal region.

4) Screen these materials for agronomic and genetic traits that may be of interest to the plant research community.

All 10 maize chromosomes have been successfully introduced into oat. Fertile disomic lines exist for nine of the maize chromosomes. Maize chromosome 10 addition plants have not transmitted the maize chromosome to offspring; these plants are propagated vegetatively. DNA is available for all 10 oat-maize chromosome addition lines. Transmission of the maize chromosome is nearly 100% in a majority of the addition lines. The disomic addition plants carrying chromosome 1, chromosome 5, chromosome 7 and chromosome 8 exhibited irregular transmission of the respective maize chromosome in early generations. Through selection we have obtained offspring for the disomic chromosome 1 and the chromosome 7 addition lines that transmit the maize chromosome nearly 100% of the time. Selection is underway with the chromosome 5 and chromosome 8 addition lines. We have also recovered fertile lines that carry two maize chromosomes, chromosomes 1 and 9, and chromosomes 4 and 6, each in disomic condition.

Radiation hybrid lines are derived from chromosome addition lines by irradiating seed monosomic for the maize chromosome. This treatment can fragment the maize chromosome and produce plants that carry deleted maize chromosomes and translocated maize chromosome segments. After identification and selection of appropriate offspring, maize chromosome-specific panels of radiation hybrid lines are produced and used to map sequences. Low-resolution mapping panels are nearing completion for chromosomes 2 and 9. The low-resolution panels will contain approximately 10 radiation hybrid lines enabling researchers to rapidly map a marker to a chromosomal region. High-resolution panels will then be generated using larger numbers of radiation hybrid lines with a goal to be able to map to a 1-2 Mb region.

Efforts are being made to adapt microarray technology for mapping ESTs with chromosome addition lines. Genomic DNA from maize, oat, and addition lines will be labeled and hybridized to EST sequences immobilized on glass slides. Hybridization with maize genomic DNA provides the positive control, and hybridization with oat genomic DNA provides the negative control. ESTs will be located to chromosome when the hybridization signal from an addition line is significantly above the signal with oat genomic DNA and close to the signal with maize genomic DNA. Preliminary experiments have demonstrated the ability to discriminate between oat and maize sequences with this technology.

An oat-maize addition line represents the introduction of thousands of maize genes into oat. Some of these genes give a visible phenotype. A liguleless3 (lg3) transcript was detected in the chromosome 3 addition lines, and these lines have liguleless upper leaves and frequently a hooked panicle, which is consistent with the variant phenotype seen in maize Lg3 plants (Muehlbauer, G et al., Genome 43:1055, 2000). The variant phenotype was observed in two independent chromosome 3 addition lines; one addition line was derived from the oat cultivar Preakness and the other from Sun II oat. Other maize chromosomes also have been introduced into different oat cultivars to investigate the effect of the oat background on the expression of maize genes. Efforts are being made to screen for characters such as disease resistance and photoperiod response in this material.

More information about the project, materials available, traits observed, and publications can be found at: // This work was sponsored by NSF Grant No. 9872650. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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