An annotated reference sequence representing the hexaploid bread wheat genome in 21 pseudomolecules has been analyzed to identify the distribution and genomic context of coding and noncoding elements across the A, B, and D subgenomes. With an estimated coverage of 94% of the genome and containing 107,891 high-confidence gene models, this assembly enabled the discovery of tissue- and developmental stage–related coexpression networks by providing a transcriptome atlas representing major stages of wheat development. Dynamics of complex gene families involved in environmental adaptation and end-use quality were revealed at subgenome resolution and contextualized to known agronomic single-gene or quantitative trait loci. This community resource establishes the foundation for accelerating wheat research and application through improved understanding of wheat biology and genomics-assisted breeding.

Because of their abundance and their amenability to high-throughput genotyping techniques, Single Nucleotide Polymorphisms (SNPs) are powerful tools for efficient genetics and genomics studies, including characterization of genetic resources, genome-wide association studies and genomic selection. In wheat, most of the previous SNP discovery initiatives targeted the coding fraction, leaving almost 98% of the wheat genome largely unexploited. Here we report on the use of whole-genome resequencing data from eight wheat lines to mine for SNPs in the genic, the repetitive and non-repetitive intergenic fractions of the wheat genome. Eventually, we identified 3.3 million SNPs, 49% being located on the B-genome, 41% on the A-genome and 10% on the D-genome. We also describe the development of the TaBW280K high-throughput genotyping array containing 280,226 SNPs. Performance of this chip was examined by genotyping a set of 96 wheat accessions representing the worldwide diversity. Sixty-nine percent of the SNPs can be efficiently scored, half of them showing a diploid-like clustering. The TaBW280K was proven to be a very efficient tool for diversity analyses, as well as for breeding as it can discriminate between closely related elite varieties. Finally, the TaBW280K array was used to genotype a population derived from a cross between Chinese Spring and Renan, leading to the construction a dense genetic map comprising 83,721 markers. The results described here will provide the wheat community with powerful tools for both basic and applied research.

During meiosis, crossovers (COs) create new allele associations by reciprocal exchange of DNA. In bread wheat (Triticum aestivum L.), COs are mostly limited to subtelomeric regions of chromosomes, resulting in a substantial loss of breeding efficiency in the proximal regions, though these regions carry 60-70% of the genes. Identifying sequence and/or chromosome features affecting recombination occurrence is thus relevant to improve and drive recombination. Using the recent release of a reference sequence of chromosome 3B and of the draft assemblies of the 20 other wheat chromosomes, we performed fine-scale mapping of COs and revealed that 82% of COs located in the distal ends of chromosome 3B representing 19% of the chromosome length. We used 774 SNPs to genotype 180 varieties representative of the Asian and European genetic pools and a segregating population of 1270 F 6 lines. We observed a common location for ancestral COs (predicted through linkage disequilibrium) and the COs derived from the segregating population. We delineated 73 small intervals (,26 kb) on chromosome 3B that contained 252 COs. We observed a significant association of COs with genic features (73 and 54% in recombinant and nonrecombinant intervals, respectively) and with those expressed during meiosis (67% in recombinant intervals and 48% in nonrecombinant intervals). Moreover, while the recombinant intervals contained similar amounts of retrotransposons and DNA transposons (42 and 53%), nonrecombinant intervals had a higher level of retrotransposons (63%) and lower levels of DNA transposons (28%). Consistent with this, we observed a higher frequency of a DNA motif specific to the TIR-Mariner DNA transposon in recombinant intervals. KEYWORDS recombination; meiosis; bread wheat; linkage disequilibrium; transposon; hotspot; sequence motif M EIOTIC recombination is a process that allows reshuffling of diversity by the reciprocal exchange of DNA called a crossover (CO). This phenomenon is conserved in most eukaryotes (for a review see Mercier et al. 2015) and follows the formation of a double-strand break (DSB) of DNA generated by the topoisomerase SPO11 complex. However, the number of DSBs is at least 10-to 50-fold greater than the number of COs which rarely exceeds three per bivalent chromosome per meiosis (Mercier et al. 2015). This paucity of COs per meiosis with regards to the number of DSBs suggests the existence of a tight control and regulation of recombination in plants that promote DSB repair in a manner that does not lead to COs. For example, the study of the two helicases AtFANCM and RECQ4 (AtRECQ4A and AtRECQ4B) (Crismani et al. 2012;Knoll et al. 2012;Girard et al. 2014;Séguéla-Arnaud et al. 2015) revealed three-and sixfold CO frequency increases in the Atfancm single mutant and the Atrecq4a/Atrecq4b double mutant, respectively, compared to the wild type. These increases result from additional COs from the class-II pathway which suggests that FANCM and RECQ4 prevent CO formation and direct recombination intermediates towar...

We compared the performance of two commonly used genotyping platforms, genotyping-by-sequencing (GBS) and single nucleotide polymorphism-arrays (SNP), to investigate the extent and pattern of genetic variation within a collection of 1,000 diverse barley genotypes selected from the German Federal ex situ GenBank hosted at IPK Gatersleben. Each platform revealed equivalent numbers of robust bi-allelic SNPs (39,733 and 37,930 SNPs for the 50K SNP-array and GBS datasets respectively). A small overlap of 464 SNPs was common to both platforms, indicating that the methodologies we used selectively access informative polymorphism in different portions of the barley genome. Approximately half of the GBS dataset was comprised of SNPs with minor allele frequencies (MAFs) below 1%, illustrating the power of GBS to detect rare alleles in diverse germplasm collections. While desired for certain applications, the highly robust calling of alleles at the same SNPs across multiple populations is an advantage of the SNP-array, allowing direct comparisons of data from related or unrelated studies. Overall MAFs and diversity statistics (π) were higher for the SNP-array data, potentially reflecting the conscious removal of markers with a low MAF in the ascertainment population. A comparison of similarity matrices revealed a positive correlation between both approaches, supporting the validity of using either for entire GenBank characterization. To explore the potential of each dataset for focused genetic analyses we explored the outcomes of their use in genome-wide association scans for row type, growth habit and non-adhering hull, and discriminant analysis of principal components for the drivers of sub-population differentiation. Interpretation of the results from both types of analysis yielded broadly similar conclusions indicating that choice of platform used for such analyses should be determined by the research question being asked, group preferences and their capabilities to extract and interpret the different types of output data easily and quickly. Access to the requisite infrastructure for running, processing, analyzing, querying, storing, and displaying either datatype is an additional consideration. Our investigations reveal that for barley the cost per genotyping assay is less for SNP-arrays than GBS, which translates to a cost per informative datapoint being significantly lower for the SNP-array.