Molecular Characterization of Threshability Genes, Sog and Tg in Wheat.

Threshability is an important agronomic trait in wheat as free-threshing forms facilitate mechanical threshing of grain. All wild relatives of wheat have tough glumes and are non-free-threshing whereas most cultivated wheats have soft glumes and are free-threshing. Two genetic loci are known to govern the threshability trait in bread wheat. The Q gene located on chromosome 5AL along with tough glume genes located on homoeologous group-2 chromosomes seem to interact to produce a free-threshing phenotype. The Q gene has recently been isolated and found to be a member of AP2 class of transcription factors whereas only a few studies have been done so far to characterize the tough glume genes on group-2 chromosomes. We mapped the soft glume (Sog) gene of Triticum monococcum and tenacious glume (Tg) gene of T. aestivum on short arm of chromosome 2A^m and 2D respectively. Comparative mapping of Sog and Tg genes indicated their non-syntenous positions on homoeologous group-2 chromosomes. The Sog gene was mapped in a low-recombination region near the centromere on 2A^mS whereas genomic targeting of Tg using deletion bin mapped ESTs assigned this gene to the distal 16% of the chromosome 2DS. Localization of Tg in the high-recombination gene-rich region indicates the feasibility of its isolation using map-based cloning. Thus we are investigating the wheat-rice synteny and other available genomic resources in Triticeae to isolate this important agronomic gene.