Map-based analysis of genetic loci on chromosome 2D that affect glume tenacity and threshability, components of the free-threshing habit in common wheat (Triticum aestivum L.)

Abstract

During the domestication of bread wheat (Triticum aestivum L.), evolutionary modifications that took place in seed dispersal mechanisms enhanced its suitability for agricultural production. One of these modifications involved the evolution of the free-threshing or hulless characteristic. In this study, we studied quantitative trait loci (QTL) affecting components of the free-threshing habit (threshability and glume tenacity) on chromosome 2D in a recombinant inbred line (RIL) population developed by the International Triticeae Mapping Initiative (ITMI) as well as the tenacious glumes 1 (Tg1) gene in F(2) progeny (CS/CS2D F(2)) of a cross between Chinese Spring and the 2D2 substitution line [Chinese Spring (Ae. tauschii 2D)]. In the ITMI population, two QTL affected threshability (QFt.orst-2D.1 and QFt.orst-2D.2) and their location coincided with QTL affecting glume tenacity (QGt.orst-2D.1 and QGt.orst-2D.2). In the CS/CS2D F(2) population, the location of QTL that affected glume tenacity (QGt.orst-2D.1), the size of a glume base scar after detachment (QGba.orst-2D), and Tg1 (12-cM interval between Xwmc112 and Xbarc168) also coincided. Map comparisons suggest that QFt-orst-2D.1, QGt.orst-2D.1, and QGba.orst-2D correspond to Tg1 whereas QFt.orst-2D.2 and QGt.orst-2D.2 appear to represent separate loci. The observation of coincident QTL for threshability and glume tenacity suggests that threshability is a function of glume adherence. In addition, the observation of the coincident locations of Tg1 and QTL for the force required to detach a glume and the size of a glume base scar after detachment suggests that Tg1's effect on both glume tenacity and threshability resides on its ability to alter the level of physical attachment of glumes to the rachilla of a spikelet.

Genes and Mutations Underlying Domestication Transitions in Grasses

“…When tetraploid wheat with such a genotype was crossed with A. tauschii, the DD-genome parent of the bread wheat, the synthetic hexaploid was not free threshing due to the presence of the dominant allele at the Tg locus of the DD genome (Kerber and Rowland, 1974). Thus, an additional recessive mutation at the Tg locus of the DD genome was required for the development of the free-threshing condition in the hexaploid bread wheat, which gave rise to the genotype of tgtg 2B tgtg 2D QQ 5A (Jantasuriyarat et al, 2004;Nalam et al, 2007).…”

Seed shattering in a wild sorghum is conferred by a locus unrelated to domestication

“…The fixation of sh4 occurred very early in rice domestication with the domesticated allele occurring in both subspecies indica and japonica, whereas qSH1 is much more recent, present only within temperate japonica genotypes (10,11). In wheat, quantitative trait loci (QTLs) responsible for nonbrittle rachis are located in the homeologous regions of chromosome 3A (Br2), 3B (Br3), and 3D (Br1) (12,13). Comparative mapping hinted that this part of the chromosomal regions might correspond to the orthologous region in barley, controlled by two tightly linked loci, Btr1 and Btr2, but do not appear to correspond to the region in other major cereals (12,13).…”

“…In wheat, quantitative trait loci (QTLs) responsible for nonbrittle rachis are located in the homeologous regions of chromosome 3A (Br2), 3B (Br3), and 3D (Br1) (12,13). Comparative mapping hinted that this part of the chromosomal regions might correspond to the orthologous region in barley, controlled by two tightly linked loci, Btr1 and Btr2, but do not appear to correspond to the region in other major cereals (12,13). Indeed, although some shattering genes do appear to be in corresponding (orthologous) chromosomal locations among cereals (2), many do not; therefore, it is hypothesized that there are multiple pathways responsible for seed dispersal in the grasses (14).…”

Genotyping of the Q locus in wheat by a simple PCR-RFLP method

“…Q undoubtedly played an important role in evolution of domesticated wheat and subsequent widespread cultivation of emmer and common wheat (for review see Salamini et al, 2002;Faris et al, 2005). There occurs, however, a wide range of phenotypic variation in wheat accessions with the same Q locus genotype because Qcontrolled traits are also regulated by other quantitative trait loci (Kato et al, 1999;Simonetti et al, 1999;Jantasuriyarat et al, 2004;Nalam et al, 2007). For instance, threshability is also regulated at least by a partially recessive allele at another locus designated Tg (Tenacious glume) on the short arm of chromosome 2B (Kerber and Rowland, 1974;Nalam et al, 2007).…”