Abstract
Tibetan wheat is grown under environmental constraints at high-altitude conditions, but its underlying adaptation mechanism remains unknown. Here, we present a draft genome sequence of a Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum Shao) accession Zang1817 and re-sequence 245 wheat accessions, including world-wide wheat landraces, cultivars as well as Tibetan landraces. We demonstrate that high-altitude environments can trigger extensive reshaping of wheat genomes, and also uncover that Tibetan wheat accessions accumulate high-altitude adapted haplotypes of related genes in response to harsh environmental constraints. Moreover, we find that Tibetan semi-wild wheat is a feral form of Tibetan landrace, and identify two associated loci, including a 0.8-Mb deletion region containing Brt1/2 homologs and a genomic region with TaQ-5A gene, responsible for rachis brittleness during the de-domestication episode. Our study provides confident evidence to support the hypothesis that Tibetan semi-wild wheat is de-domesticated from local landraces, in response to high-altitude extremes.
Highlights
Tibetan wheat is grown under environmental constraints at high-altitude conditions, but its underlying adaptation mechanism remains unknown
It is estimated that wheat was introduced into China ~5000 years ago, and planted in Tibet as early as ~3500 years ago[39]
We report that the colonization of wheat in the Tibetan Plateau appears to have co-selected primitive sequence diversity and postfixation of haplotypes for adaptation in high-altitude environments including, high light intensities, low temperature and hypoxia stresses in addition to photoperiod response
Summary
Tibetan wheat is grown under environmental constraints at high-altitude conditions, but its underlying adaptation mechanism remains unknown. Hexaploid wheat is widely distributed around the world, including the Tibetan Plateau, which has an average altitude of 4268 m above sea level[6], and is characterized by extensive UV-B irradiation, extremely low temperature and strong hypoxia stress Such environmental constraints would be expected to trigger genomic variation of wheat associated with adaptation to high-altitude (HA), the underlying molecular changes are still unknown. Tibetanum Shao) is discovered on the Tibetan Plateau, China[7] Huang and his colleagues[6] investigated 17 agronomic traits of 77 Tibetan accessions and 277 Tibetan semi-wild wheat, and found that Tibetan semi-wild wheat phenotypically resembles Tibetan local landraces but differs in brittle rachis characteristics (Fig. 1a). We uncover a feral origin of Tibetan semi-wild wheat, which is probably, in effect, a de-domesticated form of Tibetan landraces, suggesting that the Tibetan wheat is a resource for fine tuning wheat germplasm to certain environments
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