RECENT ADVANCES IN THE PHYSICAL MAPPING OF WHEAT CHROMOSOME 5A

High density genetic maps, needed for anchoring BAC contigs during the construction of a physical map and for DNA sequence assembly, have been developed for the short arm of wheat chromosome 5A (5AS). To undertake this challenge we relied on four mapping populations: [1] Chinese Spring (CS, Triticum aestivum) x Renan (T. aestivum); [2] CS x CS disomic substitution line for chr. 5A (T. turgidum ssp dicoccoides); [3] Latino (T. turgidum ssp durum) x MG5323 (T. turgidum ssp dicoccum); [4] DV92 (T. monococcum) x G3116 (T. monococcum). Different approaches for marker development were implemented: a) a set of SSRs (simple sequence repeats) from databases and literature, b) a set of COS (conserved ortholog set) comparative markers, c) ESTs (expressed sequence tag) specific for 5A, d) SSR, and TE (trasponable elements) junction markers were screened from a 2x coverage of 454 sequences run on 5AS flow sorted DNA. The specificity of these markers for chromosome 5AS has been assessed using nulli-tetrasomic lines derived from the cultivar CS, while their physical position has been assigned to deletion bins of 5AS through the utilization of deletion lines. The anchoring between the four genetic linkage maps and the 4201 BAC clones of the MTP (minimal tiling path), produced after HICF (high information content fingerprinting) analysis of about 45.000 BACs and organized in 3D pools, is in progress. Additional specific markers are being developed from the sequencing of 2000 BAC-ends obtained from BACs of the MTP in order to improve the link between the genetic and physical map. High density genetic maps are under development also for 5AL, and the anchoring to 3D pools of the 6560 MTP-BAC clones deriving from the HICF analysis of about 50.000 BACs, has already started with the available markers mapped.