High-density physical maps reveal that the dominant male-sterile gene Ms3 is located in a genomic region of low recombination in wheat and is not amenable to map-based cloning

In wheat it is essential to know whether a gene is located in a high or low recombination region of the genome before initiating a map-based cloning a pproach. The objective of this study was to explore the potential feasibili ty of map-based cloning of the dominant male-sterile gene Ms3 of wheat. Hig h-density physical maps of the short arms of the group-5 chromosomes (5AS, 5BS, and 5DS) of Triticum aestivum L. were constructed by mapping 40 DNA ma rkers on a set of 17 homozygous deletion lines. One hundred RFLP loci were mapped: 35 on 5AS, 37 on 5BS, and 28 on 5DS. A consensus physical map was c olinearly aligned with a consensus genetic map of the group-5 short arms. S ixteen of the 17 markers in the consensus genetic map encompass a genetic d istance of 25 cM and correspond to the distal region (FL 0.56-0.97) of the consensus physical map. Two rice probes, RG463 and RG901, previously identi fied to be linked to markers CDO344 and CD0749 (group-5 short arm of wheat) , respectively, in the genetic map of rice chromosome 12, map between FL 0. 56 and 0.63 in the consensus map. Thus at least a part of the group-5 short arm is homoeologous to a region of chromosome 12 of rice. The genetic map of chromosome arrn 5AS was constructed using a population of 139 BC, plants derived from a cross between the euploid wheat "Chris" carrying a dominant male-sterile gene Ms3 and a disomic substitution line in which chromosome 5A of T aestivum cv Chinese Spring was substituted by chromosome 5A from Tr iticum turgidum ssp. dicoccoides. The map has a genetic length of 53.4 cM w ith 11 DNA markers. The initial map showed that the gene Ms3 cosegregated w ith three markers, WG341, BCD1130 and CD0677. High-resolution mapping using an additional 509 BC, plants indicated that the marker WG341 was closely l inked to Ms3 at a genetic distance of 0.8 cM. The Ms3 was mapped physically in the region spanning 40% of the arm length from the centromere of 5AS. T herefore, mapbased cloning of the Ms3 is not feasible, although WG341 can b e used as a useful tag for the Ms3 gene for breeding purposes.