Genome Plasticity a Key Factor in the Success of Polyploid Wheat Under Domestication

Department of Plant Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA.
Science (Impact Factor: 33.61). 07/2007; 316(5833):1862-6. DOI: 10.1126/science.1143986
Source: PubMed


Wheat was domesticated about 10,000 years ago and has since spread worldwide to become one of the major crops. Its adaptability to diverse environments and end uses is surprising given the diversity bottlenecks expected from recent domestication and polyploid speciation events. Wheat compensates for these bottlenecks by capturing part of the genetic diversity of its progenitors and by generating new diversity at a relatively fast pace. Frequent gene deletions and disruptions generated by a fast replacement rate of repetitive sequences are buffered by the polyploid nature of wheat, resulting in subtle dosage effects on which selection can operate.

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Available from: Jan Dvorak, Apr 01, 2014
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    • "Bread wheat (Triticum aestivum) is an allohexaploid crop derived from the hybridization of diploid Aegilops tauschii with tetraploid wild emmer, Triticum turgidum ssp. dicoccoides (Dubcovsky and Dvorak, 2007; Matsuoka, 2011; Shewry, 2009). This hybridization , subsequent domestication and inbreeding have reduced genetic diversity in cultivated wheat compared with its wild ancestors (Haudry et al., 2007; Tanksley and McCouch, 1997). "
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    ABSTRACT: In wheat, a lack of genetic diversity between breeding lines has been recognized as a significant block to future yield increases. Species belonging to bread wheat's secondary and tertiary gene pools harbour a much greater level of genetic variability, and are an important source of genes to broaden its genetic base. Introgression of novel genes from progenitors and related species has been widely employed to improve the agronomic characteristics of hexaploid wheat, but this approach has been hampered by a lack of markers that can be used to track introduced chromosome segments. Here, we describe the identification of a large number of single nucleotide polymorphisms that can be used to genotype hexaploid wheat and to identify and track introgressions from a variety of sources. We have validated these markers using an ultra-high-density Axiom® genotyping array to characterize a range of diploid, tetraploid and hexaploid wheat accessions and wheat relatives. To facilitate the use of these, both the markers and the associated sequence and genotype information have been made available through an interactive web site.
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    • "WGD has been implicated in speciation and biodiversification, providing new genetic combinations in natural populations to favour evolution and increasing organism complexity (Soltis et al., 2014). In addition , polyploidy has played an essential role in the domestication of many crops, such as maize, wheat, and cotton (Dubcovsky and Dvorak, 2007). Recent and ancient polyploidization events occurred in plants with a high frequency, particularly in angiosperms. "
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    ABSTRACT: Polyploidy is a common event in plants that involves the acquisition of more than two complete sets of chromosomes. Allopolyploidy originates from interspecies hybrids while autopolyploidy originates from intraspecies whole genome duplication (WGD) events. In spite of inconveniences derived from chromosomic rearrangement during polyploidiza-tion, natural plant polyploids species often exhibit improved growth vigour and adaptation to adverse environments, conferring evolutionary advantages. These advantages have also been incorporated into crop breeding programmes. Many tetraploid crops show increased stress tolerance, although the molecular mechanisms underlying these different adaptation abilities are poorly known. Understanding the physiological, cellular, and molecular mechanisms coupled to WGD, in both allo-and autopolyploidy, is a major challenge. Over the last few years, several studies, many of them in Arabidopsis, are shedding light on the basis of genetic, genomic, and epigenomic changes linked to WGD. In this review we summarize and discuss the latest advances made in Arabidopsis polyploidy, but also in other agro-nomic plant species.
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    • "dicoccum (2n = 4x =28, AABB) c. 9000 yr ago (Nesbitt & Samuel, 1996). During the course of cultivation of domesticated tetraploid wheat T. dicoccum (AABB), it hybridized with diploid species Aegilops tauschii (2n = 2x = 14, DD) to form hexaploid wheat, T. aestivum (2n = 6x =42, AABBDD) (McFaden & Sears, 1946; Dvorak, 1976; Dubcovsky & Dvorak, 2007; Matsuoka, 2011). "
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    ABSTRACT: Preharvest sprouting (PHS) is one of the major constraints of wheat production in areas where prolonged rainfall occurs during harvest. TaPHS1 is a gene that regulates PHS resistance on chromosome 3A of wheat, and two causal mutations in the positions +646 and +666 of the TaPHS1 coding region result in wheat PHS susceptibility. Three competitive allele-specific PCR (KASP) markers were developed based on the two mutations in the coding region and one in the promoter region and validated in 82 wheat cultivars with known genotypes. These markers can be used to transfer TaPHS1 in breeding through marker-assisted selection. Screening of 327 accessions of wheat A genome progenitors using the three KASP markers identified different haplotypes in both diploid and tetraploid wheats. Only one Triticum monococcum accession, however, carries both causal mutations in the TaPHS1 coding region and shows PHS susceptibility. Five of 249 common wheat landraces collected from the Fertile Crescent and surrounding areas carried the mutation (C) in the promoter (−222), and one landrace carries both the causal mutations in the TaPHS1 coding region, indicating that the mis-splicing (+646) mutation occurred during common wheat domestication. PHS assay of wheat progenitor accessions demonstrated that the wild-types were highly PHS-resistant, whereas the domesticated type showed increased PHS susceptibility. The mis-splicing TaPHS1 mutation for PHS susceptibility was involved in wheat domestication and might arise independently between T. monococcum and Triticum aestivum.
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