Submitted to: Genome Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/13/2002
Publication Date: 6/21/2002
Citation: Faris, J.D., Gill, B.S. 2002. Polyploid genome analysis: genomic targeting and high-resolution mapping of the domestication gene q in wheat. Genome 45:706-718. Interpretive Summary: Crop plants have undergone certain genetic changes through evolution that allowed them to become domesticated. For domesticated bread wheat, the free-threshing characteristic of the spike is probably the most important domestication trait. The Q gene is responsible for conditioning the free-threshing character, but it also has influence on other important domestication traits such as rachis toughness, glume tenacity, spike length, and plant height. The Q gene has been located on the long arm of chromosome 5A in wheat. Using modern molecular techniques in combination with unique cytogenetic stocks of wheat, we identified molecular markers tightly linked to the Q gene. These markers, and other genomic information obtained in this study, provide a basis for cloning the Q gene. Once the Q gene is isolated, we will be able to study the regulatory effects that Q has on other genes and dissect the biochemical pathways. Furthermore, Q may be used to domesticate other wild wheat species by transformation, rendering them useful for cultivation in order to exploit value added traits.
Technical Abstract: The Q locus is largely responsible for the domestication of bread wheat. Q confers the free-threshing character of the spike and influences other important agronomic traits. Using chromosome deletion lines, Q was placed on the physical map within a submicroscopic segment of the long arm of chromosome 5A. We targeted markers to the segment by comparative mapping of anonymous RFLP clones, AFLP, and mRNA differential display analysis of deletion lines 5AL-7 and 5AL-23, which have deletion breakpoints flanking the Q locus. Differentially expressed sequences detected fragments at various loci on group 5 chromosomes suggesting that Q may be a regulatory gene. We identified 18 markers within the Q gene deletion interval and used them to construct a genetic linkage map of the region in F2 populations derived from chromosome 5A disomic substitution lines. The genetic map corresponding to the deletion segment was 20 cM long, and we identified markers as close as 0.7 cM to the Q gene. An estimate of the base pair/cM ratio within the region is 250 kb/cM, an 18-fold increase in recombination compared to the genomic average. Genomic targeting and high-density mapping provide a basis for the map-based cloning of the Q gene.