Genome-Wide Quantitative Trait Locus Mapping Identifies Multiple Major Loci for Brittle Rachis and Threshability in Tibetan Semi-Wild Wheat (Triticum aestivum ssp. tibetanum Shao)

Abstract

Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum Shao) is a semi-wild hexaploid wheat resource that is only naturally distributed in the Qinghai-Tibet Plateau. Brittle rachis and hard threshing are two important characters of Tibetan semi-wild wheat. A whole-genome linkage map of T. aestivum ssp. tibetanum was constructed using a recombinant inbred line population (Q1028×ZM9023) with 186 lines, 564 diversity array technology markers, and 117 simple sequence repeat markers. Phenotypic data on brittle rachis and threshability, as two quantitative traits, were evaluated on the basis of the number of average spike rachis fragments per spike and percent threshability in 2012 and 2013, respectively. Quantitative trait locus (QTL) mapping performed using inclusive composite interval mapping analysis clearly identified four QTLs for brittle rachis and three QTLs for threshability. However, three loci on 2DS, 2DL, and 5AL showed pleiotropism for brittle rachis and threshability; they respectively explained 5.3%, 18.6%, and 18.6% of phenotypic variation for brittle rachis and 17.4%, 13.2%, and 35.2% of phenotypic variation for threshability. A locus on 3DS showed an independent effect on brittle rachis, which explained 38.7% of the phenotypic variation. The loci on 2DS and 3DS probably represented the effect of Tg and Br1, respectively. The locus on 5AL was in very close proximity to the Q gene, but was different from the predicted q in Tibetan semi-wild wheat. To our knowledge, the locus on 2DL has never been reported in common wheat but was prominent in T. aestivum ssp. tibetanum accession Q1028. It remarkably interacted with the locus on 5AL to affect brittle rachis. Several major loci for brittle rachis and threshability were identified in Tibetan semi-wild wheat, improving the understanding of these two characters and suggesting the occurrence of special evolution in Tibetan semi-wild wheat.

Re‐acquisition of the brittle rachis trait via a transposon insertion in domestication gene Q during wheat de‐domestication

“…Our study has provided a new example from a polyploid species, hexaploid wheat, enabling a comparison of the de‐domestications of rice and wheat. Brittle rachises (equivalent to seed shattering in rice) (Cao et al ., ; Chen et al ., ; Jiang et al ., ) and seed dormancy (Lan et al ., ; Jiang et al ., ) are typical features of both Tibetan semi‐wild wheat and weedy rice. In weedy rice, the re‐acquisition of seed shattering was driven by novel genes resulting from mutations (Thurber et al ., ; Subudhi et al ., ; Qi et al ., ; Yao et al ., ), and the development of seed dormancy was due to both pre‐existing variations and new mutations (Gross et al ., ; Xia et al ., ).…”

“…Jiang et al . () identified three unique loci (i.e. Qbr.sau‐5A , Br1 3D and Qbr.sau‐2D2 ) for the brittle rachis trait, suggesting that Tibetan semi‐wild wheat regained seed dispersal mechanisms through new mutations during de‐domestication.…”

“…Genetic studies have revealed that Tibetan semi‐wild wheat contains a set of unique loci controlling the brittle rachis trait. A major locus was mapped on chromosome 3DS and was designated as Br1 3D (Chen et al ., ; Chen, ; Watanabe et al ., ; Jiang et al ., ). We identified another two major loci for the brittle rachis trait, namely Qbr.sau‐5A on chromosome 5AL (i.e.…”

Genetic analysis of glume hairiness (Hg) gene in bread wheat (Triticum aestivum L.)

“…The whole-genome genetic maps were constructed using SSR and DArT markers as described previously (Jiang et al 2014). Hg trait was incorporated into the constructed maps to detect its linkage to all of the 21 chromosomes.…”

The evolution of crops that do not need us anymore

“…() attacked the puzzle by summoning multiple techniques to study the function and evolution of one of the three major loci for the brittle rachis trait in TSWW. Their previous work (Jiang et al ., ) identified those loci. In the study at hand they focused on the nonshattering Qbr.sau‐5A gene on chromosome 5AL using near‐isogenic lines and employing a variety of molecular, phylogenetic and phenotypic analyses.…”