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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.

Hexaploid wheat (Triticum aestivum, genomes AABBDD) originated by hybridization of tetraploid Triticum turgidum (genomes AABB) with Aegilops tauschii (genomes DD). Genetic relationships between A. tauschii and the wheat D genome are of central importance for the understanding of wheat origin and subsequent evolution. Genetic relationships among 477 A. tauschii and wheat accessions were studied with the A. tauschii 10K Infinium single nucleotide polymorphism (SNP) array. Aegilops tauschii consists of two lineages (designated 1 and 2) having little genetic contact. Each lineage consists of two closely related sublineages. A population within lineage 2 in the southwestern and southern Caspian appears to be the main source of the wheat D genome. Lineage 1 contributed as little as 0.8% of the wheat D genome. Triticum aestivum is subdivided into the western and Far Eastern populations. The Far Eastern population conserved the genetic make-up of the nascent T. aestivum more than the western population. In wheat, diversity is high in chromosomes 1D and 2D and it correlates in all wheat D-genome and A. tauschii chromosomes with recombination rates. Gene flow from A. tauschii was an important source of wheat genetic diversity and shaped its distribution along the D-genome chromosomes.

Powdery mildew, caused by Blumeria graminis f. sp. tritici ( Bgt ), is one of the most destructive diseases that pose a great threat to wheat production. Wheat landraces represent a rich source of powdery mildew resistance. Here, we report the map-based cloning of powdery mildew resistance gene Pm24 from Chinese wheat landrace Hulutou. It encodes a tandem kinase protein (TKP) with putative kinase-pseudokinase domains, designated WHEAT TANDEM KINASE 3 (WTK3). The resistance function of Pm24 was validated by transgenic assay, independent mutants, and allelic association analyses. Haplotype analysis revealed that a rare 6-bp natural deletion of lysine-glycine codons, endemic to wheat landraces of Shaanxi Province, China, in the kinase I domain (Kin I) of WTK3 is critical for the resistance function. Transgenic assay of WTK3 chimeric variants revealed that only the specific two amino acid deletion, rather than any of the single or more amino acid deletions, in the Kin I of WTK3 is responsible for gaining the resistance function of WTK3 against the Bgt fungus. Powdery mildew is a major threat to world wheat yields. Here the authors describe the map-based cloning of Pm24 , a gain-of-function powdery mildew resistance allele that encodes a tandem kinase-pseudokinase protein with a deletion in a kinase domain that is endemic to certain wheat landraces.

In this paper a concept for the efficient design of a series of floating fractional-order elements (FOEs) is proposed. Using even single or a very limited number of so-called “seed” FOEs it is possible to obtain a wide set of new FOEs featuring fractional order α being in the range [−n,n], where n is an arbitrary integer number, and hence enables to overcome the lack of commercial unavailability of FOEs. The systematic design stems from the utilization of a general immittance converter (GIC), whereas the concept is further developed by proposing a general circuit structure of the GIC that employs operational transconductance amplifiers (OTAs) as active elements. To show the efficiency of the presented approach, the use of only up to two “seed” FOEs with a properly selected fractional order αseed as passive elements results in the design of a series of 51 FOEs with different α being in the range [−2,2] that may find their utilization in sensor applications and the design of analog signal processing blocks. Comprehensive analysis of the proposed GIC is given, whereas the effect of parasitic properties of the assumed active elements is determined and the optimization process described to improve the overall performance of the GIC. Using OTAs designed in 0.18 μm TSMC CMOS technology, Cadence Virtuoso post-layout simulation results of the GIC are presented that prove its operability, performance optimization, and robustness of the proposed design concept.

Key messageComparison of genome sequences of wild emmer wheat and Aegilops tauschii suggests a novel scenario of the evolution of rearranged wheat chromosomes 4A, 5A, and 7B.Past research suggested that wheat chromosome 4A was subjected to a reciprocal translocation T(4AL;5AL)1 that occurred in the diploid progenitor of the wheat A subgenome and to three major rearrangements that occurred in polyploid wheat: pericentric inversion Inv(4AS;4AL)1, paracentric inversion Inv(4AL;4AL)1, and reciprocal translocation T(4AL;7BS)1. Gene collinearity along the pseudomolecules of tetraploid wild emmer wheat (Triticum turgidum ssp. dicoccoides, subgenomes AABB) and diploid Aegilops tauschii (genomes DD) was employed to confirm these rearrangements and to analyze the breakpoints. The exchange of distal regions of chromosome arms 4AS and 4AL due to pericentric inversion Inv(4AS;4AL)1 was detected, and breakpoints were validated with an optical Bionano genome map. Both breakpoints contained satellite DNA. The breakpoints of reciprocal translocation T(4AL;7BS)1 were also found. However, the breakpoints that generated paracentric inversion Inv(4AL;4AL)1 appeared to be collocated with the 4AL breakpoints that had produced Inv(4AS;4AL)1 and T(4AL;7BS)1. Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 either originated sequentially, and Inv(4AL;4AL)1 was produced by recurrent chromosome breaks at the same breakpoints that generated Inv(4AS;4AL)1 and T(4AL;7BS)1, or Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 originated simultaneously. We prefer the latter hypothesis since it makes fewer assumptions about the sequence of events that produced these chromosome rearrangements.

Bread wheat ( Triticum aestivum ) is a globally important crop, accounting for 20 per cent of the calories consumed by humans. Major efforts are underway worldwide to increase wheat production by extending genetic diversity and analysing key traits, and genomic resources can accelerate progress. But so far the very large size and polyploid complexity of the bread wheat genome have been substantial barriers to genome analysis. Here we report the sequencing of its large, 17-gigabase-pair, hexaploid genome using 454 pyrosequencing, and comparison of this with the sequences of diploid ancestral and progenitor genomes. We identified between 94,000 and 96,000 genes, and assigned two-thirds to the three component genomes (A, B and D) of hexaploid wheat. High-resolution synteny maps identified many small disruptions to conserved gene order. We show that the hexaploid genome is highly dynamic, with significant loss of gene family members on polyploidization and domestication, and an abundance of gene fragments. Several classes of genes involved in energy harvesting, metabolism and growth are among expanded gene families that could be associated with crop productivity. Our analyses, coupled with the identification of extensive genetic variation, provide a resource for accelerating gene discovery and improving this major crop. Sequencing of the hexaploid bread wheat genome shows that it is highly dynamic, with significant loss of gene family members on polyploidization and domestication, and an abundance of gene fragments. The bread — and barley — of life Two groups in this issue report the compilation and analysis of the genome sequences of major cereal crops — bread wheat and barley — providing important resources for future crop improvement. Bread wheat accounts for one-fifth of the calories consumed by humankind. It has a very large and complex hexaploid genome of 17 Gigabases. Michael Bevan and colleagues have analysed the genome using 454 pyrosequencing and compared it with diploid ancestral and progenitor genomes. The authors discovered significant loss of gene family members upon polyploidization and domestication, and expansion of gene classes that may be associated with crop productivity. Barley is one of the earliest domesticated plant crops. Although diploid, it has a very large genome of 5.1 Gigabases. Nils Stein and colleagues describe a physical map anchored to a high-resolution genetic map, on top of which they have overlaid a deep whole-genome shotgun assembly, cDNA and RNA-seq data to provide the first in-depth genome-wide survey of the barley genome.

The article presents a synthesis method to design electrical circuit elements with fractional-order impedance, referred to as a Fractional-Order Element (FOE) or Fractor, that can be implemented by Metal–Oxide–Semiconductor (MOS) transistors. This provides an approach to realize this class of device using current integrated circuit manufacturing technologies. For this synthesis MOS transistors are treated as uniform distributed resistive-capacitive layer structures. The synthesis approach adopts a genetic algorithm to generate the MOS structures interconnections and dimensions to realize an FOE with user-defined constant input admittance phase, allowed ripple deviations, and target frequency range. A graphical user interface for the synthesis process is presented to support its wider adoption. We synthetized and present FOEs with admittance phase from 5 to 85 degrees. The design approach is validated using Cadence post-layout simulations of an FOE design with admittance phase of 74  ± 1 degrees realized using native n-channel MOS devices in TSMC 65 nm technology. Overall, the post-layout simulations demonstrate magnitude and phase errors less than 0.5% and 0.1 degrees, respectively, compared to the synthesis expected values in the frequency band from 1 kHz to 10 MHz. This supports that the design approach is appropriate for the future fabrication and validation of FOEs using this process technology.

Wild emmer wheat (T. turgidum ssp. dicoccoides, genome BBAA) gene pool is an important source for wheat research and improvement. To utilize this resource, we hybridized wild emmer wheat (subpopulation judaicum, accession Zavitan) with durum wheat (T. turgidum ssp. durum, cv. Svevo) and developed an F₆recombinant inbred line (RIL) population. The wheat 90K iSelect SNP genotyping assay was used for genotyping of the RILs, detecting segregation for 16,387 polymorphic markers. The genetic map was constructed based on the genotypic data of 140 RILs and included a total of 14,088 markers grouped into 2,296 genetic loci in 14 linkage groups, corresponding to the 14 chromosomes of tetraploid wheat. The map was 2,110 cM long with an average distance of 0.92 cM between adjacent markers. The B genome was slightly more polymorphic (57 %) for co-dominant SNP markers than the A genome. The map included 1,012 null allele markers, in which only one SNP allele was detected, and the frequency of these markers in the B genome of wild emmer greatly exceeded that of the A genome (69 and 31 %, respectively), which may reflect a greater rate of genomic changes in the B genome. Comparison of our mapped SNP sequences with the barley genome revealed that most of the markers (92.4 %) were syntenic. This ultra-dense SNP-based genetic map with a high level of synteny to barley provides a useful framework for genetic analyses of important traits, positional cloning and marker-assisted selection, as well as for comparative genomics and genome organization studies in wheat and other cereals.

The genome sequence and its analysis of the diploid wild wheat Triticum urartu (progenitor of the wheat A genome) represent a tool for studying the complex, polyploid wheat genomes and should be a valuable resource for the genetic improvement of wheat. An A to D of wheat genomes The hexaploid genome of bread wheat Triticum aestivum , designated AABBDD, evolved as a result of hybridization between three ancestral grasses. Two papers published in the issue of Nature present genome sequences and analysis of two of these wheat progenitors. First, the genome sequence of the diploid wild wheat T. urartu (ancestor of the A genome), which resembles cultivated wheat more strongly than either Aegilops speltoides (the B ancestor) or Ae. tauschii (the D donor). And second, the Ae. tauschii genome, together with an analysis of its transcriptome. These genomes and their analyses will be powerful tools for the study of complex, polyploid wheat genomes and a valuable resource for genetic improvement of wheat. Bread wheat ( Triticum aestivum, AABBDD) is one of the most widely cultivated and consumed food crops in the world. However, the complex polyploid nature of its genome makes genetic and functional analyses extremely challenging. The A genome, as a basic genome of bread wheat and other polyploid wheats, for example, T. turgidum (AABB), T. timopheevii (AAGG) and T. zhukovskyi (AAGGA m A m ), is central to wheat evolution, domestication and genetic improvement 1 . The progenitor species of the A genome is the diploid wild einkorn wheat T. urartu 2 , which resembles cultivated wheat more extensively than do Aegilops speltoides (the ancestor of the B genome 3 ) and Ae. tauschii (the donor of the D genome 4 ), especially in the morphology and development of spike and seed. Here we present the generation, assembly and analysis of a whole-genome shotgun draft sequence of the T. urartu genome. We identified protein-coding gene models, performed genome structure analyses and assessed its utility for analysing agronomically important genes and for developing molecular markers. Our T. urartu genome assembly provides a diploid reference for analysis of polyploid wheat genomes and is a valuable resource for the genetic improvement of wheat.