Submitted to: Gene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2014
Publication Date: 6/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58904
Citation: Faris, J.D., Zhang, Z., Chao, S. 2014. Map-based analysis of the tenacious glume gene Tg-B1 of wild emmer and its role in wheat domestication. Gene. 542:198-208.
Interpretive Summary: The domestication of wheat was instrumental in spawning the civilization of humankind, and it occurred through genetic mutations that gave rise to types with non disarticulating heads, soft glumes, and free-threshing seed, which are traits that made wheat easy to cultivate, harvest, and thresh for early farmers. A well-studied gene known as Tg-D1, which confers thick, tenacious glumes that do not allow the seed to be easily liberated from the hulls, was incorporated into bread wheat via the paternal parent of bread wheat known as goatgrass. Other research has suggested that an ancestor of the maternal parent of bread wheat known as wild emmer may have also had gene(s) governing the same trait. In this research, genetic analysis of wild emmer wheat showed that, indeed, wild emmer harbors a gene similar to Tg-D1, designated Tg-B1, and it is related to Tg-D1 by ancestry. These results demonstrate that both Tg-D1 and Tg-B1 had profound influences on wheat domestication.
Technical Abstract: The domestication of wheat was instrumental in spawning the civilization of humankind, and it occurred through genetic mutations that gave rise to types with non-fragile rachises, soft glumes, and free-threshing seed. The Tg-D1 gene on chromosome 2D of Aegilops tauschii, the D-genome progenitor of hexaploid wheat, conferred tenacious glumes that prevented the seed from being free-threshing in the Triticum turgidum × Ae. tauschii amphiploid that formed 8,000 years ago and gave rise to modern day bread wheat. Wild emmer (T. turgidum ssp. dicoccoides), the AB-genome progenitor of hexaploid wheat, also has tenacious glumes, and like Tg-D1, tenacious glume genes in wild emmer must have underwent genetic mutation to give rise to free-threshing wheat. Here, we evaluated disomic substitution lines involving chromosomes 2A and 2B of wild emmer accessions substituted for homologous chromosomes in tetraploid and hexaploid backgrounds. The results suggested that both chromosomes 2A and 2B of wild emmer possess genes that inhibit threshability. A population of recombinant inbred lines derived from the tetraploid durum wheat variety Langdon crossed with a Langdon – T. turgidum ssp. dicoccoides accession PI 481521 chromosome 2B disomic substitution line was used to develop a genetic linkage map of 2B, evaluate the genetics of threshability, and map the gene derived from PI 481521 that inhibited threshability. A 2BS linkage map comprised of 58 markers was developed and markers delineated the gene to a 2.3 cM interval. Comparative analysis with maps containing the Tg-D1 locus revealed that the gene inhibiting threshability in wild emmer was homoeologous to Tg-D1 and therefore designated Tg-B1. Comparative analysis with rice and Brachypodium distachyon indicated a high level of divergence and poorly conserved colinearity, particularly near the Tg-B1 locus. These results provide a foundation for further studies involving Tg-B1, which, together with Tg-D1, had profound influences on wheat domestication.