ARS | Publication request: The Major Threshability Genes Soft Glume (sog) and Tenacious Glume (Tg), of Diploid and Polyploid Wheat, Trace Their Origin to Independent Mutations at Non-Orthologous Loci

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 9, 2009
Publication Date: May 7, 2009
Citation: Sood, S., Kuraparthy, V., Bai, G., Gill, B.S. 2009. The Major Threshability Genes Soft Glume (sog) and Tenacious Glume (Tg), of Diploid and Polyploid Wheat, Trace Their Origin to Independent Mutations at Non-Orthologous Loci. Theoretical and Applied Genetics. 119:341-351.

Interpretive Summary: Wild wheat is difficult to thresh whereas modern wheat is easy to thresh. Therefore threshability was an important trait for wheat to become a major grain crop for human consumption. The wild wheat floret is wrapped by tough glumes that make spikes difficult to thresh, whereas cultivated wheats have soft glumes and are free-threshing. In this report, we identified the chromosome locations of the soft glume (sog) gene of a diploid wheat relative, Triticum monococcum and the tenacious glume (Tg) gene of common wheat, using chromosome-specific molecular markers. The sog gene was located close to the centromere on the 2AS chromosome arm of T. monococcum whereas Tg was located in the most distal region on the chromosome arm 2DS of common wheat. The different positions suggest that the threshability mutations have independent evolutionary origins.

Technical Abstract: Threshability is an important crop domestication trait. The wild wheat progenitors have tough glumes enveloping the floret that make spikes difficult to thresh, whereas cultivated wheats have soft glumes and are free-threshing. In hexaploid wheat, the glume tenacity gene Tg along with the major domestication locus Q control threshability. The Q gene was isolated recently and found to be a member of the AP2 class of transcription factors. However, only a few studies have reported on the tough glume trait. Here we report comparative mapping of the soft glume (sog) gene of diploid Triticum monococcum L. and tenacious glume (Tg) gene of hexaploid T aestivum L. using chromosome-specific SSR and RFLP markers. The sog gene was flanked by Xgwm71 and Xbcd120 in a 6.8 cM interval on chromosome 2AmS of T. monococcum whereas Tg was targeted to a 8.1 cM interval flanked by Xwmc503 and Xfba88 on chromosome 2DS of T. aestivum. Deletion bin mapping of the flanking markers assigned sog close to the centromere on 2AS, whereas Tg was mapped to the most distal region on 2DS. Both 2AS and 2DS maps were colinear ruling out the role of chromosome rearrangements for their non-syntenic positions. Therefore sog and Tg, are not true orthologs suggesting the possibility of a diverse origin.