Location: Cereal Crops ResearchTitle: Radiation hybrid QTL mapping of Tdes2 involved in the first meiotic division of wheat) Author
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2013
Publication Date: 5/29/2013
Publication URL: http://handle.nal.usda.gov/10113/57911
Citation: Bassi, F.M., Kumar, A., Zhang, Q., Paux, E., Huttner, E., Kilian, A., Dizon, R., Feuillet, C., Xu, S.S., Kianian, S.F. 2013. Radiation hybrid QTL mapping of Tdes2 involved in the first meiotic division of wheat. Theoretical and Applied Genetics. 126:1977-1990. Interpretive Summary: Meiosis is a specific cell division responsible for production of gametes (eggs and sperms) during sexual reproduction of higher organisms. Meiosis includes two successive divisions of the nucleus to generate gametes with half the chromosomes of the mother cell. Normal pairing of homologous chromosomes (i.e., the chromosomes with the same physical features and the similar genetic characteristics) during the first divisions is essential for regular separation of homologous chromosomes into two daughter cells. The chromosome 3B in wheat harbors a gene that, when removed, causes chromosome desynapsis, which is a cytological phenomenon where paired homologous chromosomes separate early. Desynapsis causes irregular separation of chromosomes at meiosis and gamete sterility and has potential for hybrid wheat production. This gene has not been mapped and characterized with molecular markers due to the lack of natural genetic diversity. In this study, we created artificial diversity for this gene using gamma radiation treatment, which can create overlapping deletions that span the entire length of a chromosome. A population of 696 lines developed from gamma radiation was analyzed with 140 molecular markers on 3B chromosome. The occurrence of desynapsis was investigated by measuring pollen viability and seed fertility. The data generated from marker and desynapsis analysis were then used to construct a radiation hybrid map of chromosome 3B. Molecular mapping and genetic analysis revealed that the gene controlling desynapsis resides in a chromosome interval between two markers wmc326 and wPt-8983 on the long arm of chromosome 3B. The meiotic behavior of lines lacking this gene in wheat was characterized cytogenetically to reveal striking similarities with desynapsis mutants for a maize gene located on chromosome 3 of maize. This study represents the first example to employ radiation hybrids for genetic analysis and provides a starting point for the cloning of this interesting gene involved in meiosis of cereals.
Technical Abstract: Since the dawn of wheat cytogenetics, chromosome 3B has been known to harbor a gene(s) that, when removed, caused chromosome desynapsis and gametic sterility. The lack of natural genetic diversity for this gene(s) has prevented any attempts to fine map and further characterize it. Here, gamma radiation treatment was used to create artificial diversity for this locus. A total of 696 radiation hybrid lines were genotyped with a custom mini array of 140 DArT markers, selected to evenly span the whole 3B chromosome. The resulting map spanned 2,852 centi Ray with a calculated resolution of 0.384 Mb. Phenotyping for the occurrence of meiotic desynapsis was conducted by measuring the level of gametic sterility as seeds produced per spikelet and pollen viability at booting. Composite interval mapping revealed a single QTL with LOD of 16.2 and r2 of 25.6% between markers wmc326 and wPt-8983 on the long arm of chromosome 3B. By independent analysis, the location of the QTL was confirmed to be within the deletion bin 3BL7-0.63-1.00 and to correspond to a single gene located ~1.4 Mb away from wPt-8983. The meiotic behavior of lines lacking this gene was characterized cytogenetically to reveal striking similarities with mutants for the dy locus, located on the syntenic chromosome 3 of maize. This represents the first example to date of employing radiation hybrids for QTL analysis. The success achieved by this approach provides an ideal starting point for the final cloning of this interesting gene involved in meiosis of cereals.