Physical mapping of the 1RS chromosome arm

Numerous known and unknown wheat lines worldwide carrying the 1BL.1RS wheat-rye translocation allow to consider the short arm of the rye chromosome 1 (1RS), as an integrated part of the wheat germplasm. Therefore, investigating the genetic structure of this chromosome arm, which plays an eminent role in wheat breeding, will significantly contribute to our understanding of cereal chromosome structure and evolution. The target of this project is to assemble into contig(s) about 50,000 BAC library clones generated for the short arm of rye chromosome 1R (1RS), thus establishing the foundation for the construction of a sequence ready physical map of this chromosome arm.

From the beginning of the last century, several attempts have been made to integrate useful genetic variations of related species into cultivated hexaploid wheat by means of inter-species hybridisation. Hybridising a bread wheat cultivar (Triticum aestivum L.) with cv. `Petkus` of rye (Secale cereale L.) resulted in a spontaneous homoeologous substitution of wheat chromosome 1B by chromosome 1R of rye. Subsequent crossings of the substitution lines with regular ones led to the emergence of translocation chromosome 1BL.1RS. The presence of the short arm (1RS) in the wheat conferred resistance to several diseases caused by pathogens in wheat, including powdery mildew, leaf rust, stem rust, yellow rust and insects, as well as Russian wheat aphid, green bug and wheat curl mite, the last being the vector of the wheat streak mosaic virus. Therefore the understanding of the physical structure including the full gene content of the 1RS chromosome arm would be beneficial both for wheat and rye breeding. The aim of the present project was to dissect the 1RS chromosomal DNA ( 4.4 x 108 basepairs) to smaller entities by arranging BAC (bacterial artificial chromosome) clones representing the 1RS chromosome arm into contigs. Analysis of 50,304 BAC clones yielded 1,562 BAC contigs representing 61% of the chromosome arm DNA. The minimum tilling path is represented by about 3,500 BAC clones opening the possibility for the construction of a detailed physical map of the 1RS chromosome arm by allocation of genetic markers including genes on the assembled contigs. The results of the present study are available open access at the Wheat DB-Physical mapping database and available online at: http://probes.pw.usda.gov:8080/rye1RS/