Electronic Health Record for Forensic Dentistry

Objectives: To identify support of structured data entry for electronic health record application in forensic dentistry.

Methods: The methods of structuring information in dentistry are described and validation of structured data entry in electronic health records for forensic dentistry is performed on several real cases with the interactive DentCross component. The connection of this component to MUDR and MUDRLite electronic health records is described.

Results: The use of the electronic health record MUDRLite and the interactive DentCross component to collect dental information required by standardized Disaster Victim Identification Form by Interpol for possible victim identification is shown.

Conclusions: The analysis of structured data entry for dentistry using the DentCross component connected to an electronic health record showed the practical ability of the DentCross component to deliver a real service to dental care and the ability to support the identification of a person in forensic dentistry.

Physical Map of the Short Arm of Bread Wheat Chromosome 3D

Bread wheat ( L.) is one of the most important crops worldwide. Although a reference genome sequence would represent a valuable resource for wheat improvement through genomics-assisted breeding and gene cloning, its generation has long been hampered by its allohexaploidy, high repeat content, and large size. As a part of a project coordinated by the International Wheat Genome Sequencing Consortium (IWGSC), a physical map of the short arm of wheat chromosome 3D (3DS) was prepared to facilitate reference genome assembly and positional gene cloning. It comprises 869 contigs with a cumulative length of 274.5 Mbp and represents 85.5% of the estimated chromosome arm size. Eighty-six Mbp of survey sequences from chromosome arm 3DS were assigned in silico to physical map contigs via next-generation sequencing of bacterial artificial chromosome pools, thus providing a high-density framework for physical map ordering along the chromosome arm. About 60% of the physical map was anchored in this single experiment. Finally, 1393 high-confidence genes were anchored to the physical map. Comparisons of gene space of the chromosome arm 3DS with genomes of closely related species [ (L.) P.Beauv., rice ( L.), and sorghum [ (L.) Moench] and homeologous wheat chromosomes provided information about gene movement on the chromosome arm.

Construction of a map-based reference genome sequence for barley, Hordeum vulgare L

Barley (Hordeum vulgare L.) is a cereal grass mainly used as animal fodder and raw material for the malting industry. The map-based reference genome sequence of barley cv. ‘Morex’ was constructed by the International Barley Genome Sequencing Consortium (IBSC) using hierarchical shotgun sequencing. Here, we report the experimental and computational procedures to (i) sequence and assemble more than 80,000 bacterial artificial chromosome (BAC) clones along the minimum tiling path of a genome-wide physical map, (ii) find and validate overlaps between adjacent BACs, (iii) construct 4,265 non-redundant sequence scaffolds representing clusters of overlapping BACs, and (iv) order and orient these BAC clusters along the seven barley chromosomes using positional information provided by dense genetic maps, an optical map and chromosome conformation capture sequencing (Hi-C). Integrative access to these sequence and mapping resources is provided by the barley genome explorer (BARLEX).

The in silico identification and characterization of a bread wheat/Triticum militinae introgression line

The capacity of the bread wheat (Triticum aestivum) genome to tolerate introgression from related genomes can be exploited for wheat improvement. A resistance to powdery mildew expressed by a derivative of the cross-bread wheat cv. Tähti × T. militinae (Tm) is known to be due to the incorporation of a Tm segment into the long arm of chromosome 4A. Here, a newly developed in silico method termed rearrangement identification and characterization (RICh) has been applied to characterize the introgression. A virtual gene order, assembled using the GenomeZipper approach, was obtained for the native copy of chromosome 4A; it incorporated 570 4A DArTseq markers to produce a zipper comprising 2132 loci. A comparison between the native and introgressed forms of the 4AL chromosome arm showed that the introgressed region is located at the distal part of the arm. The Tm segment, derived from chromosome 7G, harbours 131 homoeologs of the 357 genes present on the corresponding region of Chinese Spring 4AL. The estimated number of Tm genes transferred along with the disease resistance gene was 169. Characterizing the introgression's position, gene content and internal gene order should not only facilitate gene isolation, but may also be informative with respect to chromatin structure and behaviour studies.

Flow Analysis and Sorting of Plant Chromosomes

Analysis and sorting of plant chromosomes (plant flow cytogenetics) is a special application of flow cytometry in plant genomics and its success depends critically on sample quality. This unit describes the methodology in a stepwise manner, starting with the induction of cell cycle synchrony and accumulation of dividing cells in mitotic metaphase, and continues with the preparation of suspensions of intact mitotic chromosomes, flow analysis and sorting of chromosomes, and finally processing of the sorted chromosomes. Each step of the protocol is described in detail as some procedures have not been used widely. Supporting histograms are presented as well as hints on dealing with plant material; the utility of sorted chromosomes for plant genomics is also discussed. © 2016 by John Wiley & Sons, Inc.

The Enigma of Progressively Partial Endoreplication: New Insights Provided by Flow Cytometry and Next-Generation Sequencing

In many plant species, somatic cell differentiation is accompanied by endoreduplication, a process during which cells undergo one or more rounds of DNA replication cycles in the absence of mitosis, resulting in nuclei with multiples of 2C DNA amounts (4C, 8C, 16C, etc.). In some orchids, a disproportionate increase in nuclear DNA contents has been observed, where successive endoreduplication cycles result in DNA amounts 2C + P, 2C + 3P, 2C + 7P, etc., where P is the DNA content of the replicated part of the 2C nuclear genome. This unique phenomenon was termed "progressively partial endoreplication" (PPE). We investigated processes behind the PPE in Ludisia discolor using flow cytometry (FCM) and Illumina sequencing. In particular, we wanted to determine whether chromatin elimination or incomplete genome duplication was involved, and to identify types of DNA sequences that were affected. Cell cycle analysis of root tip cell nuclei pulse-labeled with EdU revealed two cell cycles, one ending above the population of nuclei with 2C + P content, and the other with a typical "horseshoe" pattern of S-phase nuclei ranging from 2C to 4C DNA contents. The process leading to nuclei with 2C + P amounts therefore involves incomplete genome replication. Subsequent Illumina sequencing of flow-sorted 2C and 2C + P nuclei showed that all types of repetitive DNA sequences were affected during PPE; a complete elimination of any specific type of repetitive DNA was not observed. We hypothesize that PPE is part of a highly controlled transition mechanism from proliferation phase to differentiation phase of plant tissue development.

BioNano genome mapping of individual chromosomes supports physical mapping and sequence assembly in complex plant genomes

The assembly of a reference genome sequence of bread wheat is challenging due to its specific features such as the genome size of 17 Gbp, polyploid nature and prevalence of repetitive sequences. BAC-by-BAC sequencing based on chromosomal physical maps, adopted by the International Wheat Genome Sequencing Consortium as the key strategy, reduces problems caused by the genome complexity and polyploidy, but the repeat content still hampers the sequence assembly. Availability of a high-resolution genomic map to guide sequence scaffolding and validate physical map and sequence assemblies would be highly beneficial to obtaining an accurate and complete genome sequence. Here, we chose the short arm of chromosome 7D (7DS) as a model to demonstrate for the first time that it is possible to couple chromosome flow sorting with genome mapping in nanochannel arrays and create a de novo genome map of a wheat chromosome. We constructed a high-resolution chromosome map composed of 371 contigs with an N50 of 1.3 Mb. Long DNA molecules achieved by our approach facilitated chromosome-scale analysis of repetitive sequences and revealed a ~800-kb array of tandem repeats intractable to current DNA sequencing technologies. Anchoring 7DS sequence assemblies obtained by clone-by-clone sequencing to the 7DS genome map provided a valuable tool to improve the BAC-contig physical map and validate sequence assembly on a chromosome-arm scale. Our results indicate that creating genome maps for the whole wheat genome in a chromosome-by-chromosome manner is feasible and that they will be an affordable tool to support the production of improved pseudomolecules.

Chromosome identification for the carnivorous plant Genlisea margaretae

Genlisea margaretae, subgenus Genlisea, section Recurvatae (184 Mbp/1C), belongs to a plant genus with a 25-fold genome size difference and an extreme genome plasticity. Its 19 chromosome pairs could be distinguished individually by an approach combining optimized probe pooling and consecutive rounds of multicolor fluorescence in situ hybridization (mcFISH) with bacterial artificial chromosomes (BACs) selected for repeat-free inserts. Fifty-one BACs were assigned to 18 chromosome pairs. They provide a tool for future assignment of genomic sequence contigs to distinct chromosomes as well as for identification of homeologous chromosome regions in other species of the carnivorous Lentibulariaceae family, and potentially of chromosome rearrangements, in cases where more than one BAC per chromosome pair was identified.

An efficient approach to BAC based assembly of complex genomes

BACKGROUND

There has been an exponential growth in the number of genome sequencing projects since the introduction of next generation DNA sequencing technologies. Genome projects have increasingly involved assembly of whole genome data which produces inferior assemblies compared to traditional Sanger sequencing of genomic fragments cloned into bacterial artificial chromosomes (BACs). While whole genome shotgun sequencing using next generation sequencing (NGS) is relatively fast and inexpensive, this method is extremely challenging for highly complex genomes, where polyploidy or high repeat content confounds accurate assembly, or where a highly accurate 'gold' reference is required. Several attempts have been made to improve genome sequencing approaches by incorporating NGS methods, to variable success.

RESULTS

We present the application of a novel BAC sequencing approach which combines indexed pools of BACs, Illumina paired read sequencing, a sequence assembler specifically designed for complex BAC assembly, and a custom bioinformatics pipeline. We demonstrate this method by sequencing and assembling BAC cloned fragments from bread wheat and sugarcane genomes.

CONCLUSIONS

We demonstrate that our assembly approach is accurate, robust, cost effective and scalable, with applications for complete genome sequencing in large and complex genomes.

The wheat Sr50 gene reveals rich diversity at a cereal disease resistance locus

We identify the wheat stem rust resistance gene Sr50 (using physical mapping, mutation and complementation) as homologous to barley Mla, encoding a coiled-coil nucleotide-binding leucine-rich repeat (CC-NB-LRR) protein. We show that Sr50 confers a unique resistance specificity different from Sr31 and other genes on rye chromosome 1RS, and is effective against the broadly virulent Ug99 race lineage. Extensive haplotype diversity at the rye Sr50 locus holds promise for mining effective resistance genes.

Physical Mapping of Bread Wheat Chromosome 5A: An Integrated Approach

The huge size, redundancy, and highly repetitive nature of the bread wheat [Triticum aestivum (L.)] genome, makes it among the most difficult species to be sequenced. To overcome these limitations, a strategy based on the separation of individual chromosomes or chromosome arms and the subsequent production of physical maps was established within the frame of the International Wheat Genome Sequence Consortium (IWGSC). A total of 95,812 bacterial artificial chromosome (BAC) clones of short-arm chromosome 5A (5AS) and long-arm chromosome 5A (5AL) arm-specific BAC libraries were fingerprinted and assembled into contigs by complementary analytical approaches based on the FingerPrinted Contig (FPC) and Linear Topological Contig (LTC) tools. Combined anchoring approaches based on polymerase chain reaction (PCR) marker screening, microarray, and sequence homology searches applied to several genomic tools (i.e., genetic maps, deletion bin map, neighbor maps, BAC end sequences (BESs), genome zipper, and chromosome survey sequences) allowed the development of a high-quality physical map with an anchored physical coverage of 75% for 5AS and 53% for 5AL with high portions (64 and 48%, respectively) of contigs ordered along the chromosome. In the genome of grasses, Brachypodium [Brachypodium distachyon (L.) Beauv.], rice (Oryza sativa L.), and sorghum [Sorghum bicolor (L.) Moench] homologs of genes on wheat chromosome 5A were separated into syntenic blocks on different chromosomes as a result of translocations and inversions during evolution. The physical map presented represents an essential resource for fine genetic mapping and map-based cloning of agronomically relevant traits and a reference for the 5A sequencing projects.

Radiation hybrid maps of the D-genome of Aegilops tauschii and their application in sequence assembly of large and complex plant genomes

BACKGROUND

The large and complex genome of bread wheat (Triticum aestivum L., ~17 Gb) requires high resolution genome maps with saturated marker scaffolds to anchor and orient BAC contigs/ sequence scaffolds for whole genome assembly. Radiation hybrid (RH) mapping has proven to be an excellent tool for the development of such maps for it offers much higher and more uniform marker resolution across the length of the chromosome compared to genetic mapping and does not require marker polymorphism per se, as it is based on presence (retention) vs. absence (deletion) marker assay.

METHODS

In this study, a 178 line RH panel was genotyped with SSRs and DArT markers to develop the first high resolution RH maps of the entire D-genome of Ae. tauschii accession AL8/78. To confirm map order accuracy, the AL8/78-RH maps were compared with:1) a DArT consensus genetic map constructed using more than 100 bi-parental populations, 2) a RH map of the D-genome of reference hexaploid wheat 'Chinese Spring', and 3) two SNP-based genetic maps, one with anchored D-genome BAC contigs and another with anchored D-genome sequence scaffolds. Using marker sequences, the RH maps were also anchored with a BAC contig based physical map and draft sequence of the D-genome of Ae. tauschii.

RESULTS

A total of 609 markers were mapped to 503 unique positions on the seven D-genome chromosomes, with a total map length of 14,706.7 cR. The average distance between any two marker loci was 29.2 cR which corresponds to 2.1 cM or 9.8 Mb. The average mapping resolution across the D-genome was estimated to be 0.34 Mb (Mb/cR) or 0.07 cM (cM/cR). The RH maps showed almost perfect agreement with several published maps with regard to chromosome assignments of markers. The mean rank correlations between the position of markers on AL8/78 maps and the four published maps, ranged from 0.75 to 0.92, suggesting a good agreement in marker order. With 609 mapped markers, a total of 2481 deletions for the whole D-genome were detected with an average deletion size of 42.0 Mb. A total of 520 markers were anchored to 216 Ae. tauschii sequence scaffolds, 116 of which were not anchored earlier to the D-genome.

CONCLUSION

This study reports the development of first high resolution RH maps for the D-genome of Ae. tauschii accession AL8/78, which were then used for the anchoring of unassigned sequence scaffolds. This study demonstrates how RH mapping, which offered high and uniform resolution across the length of the chromosome, can facilitate the complete sequence assembly of the large and complex plant genomes.

A high-resolution physical map integrating an anchored chromosome with the BAC physical maps of wheat chromosome 6B

Background

A complete genome sequence is an essential tool for the genetic improvement of wheat. Because the wheat genome is large, highly repetitive and complex due to its allohexaploid nature, the International Wheat Genome Sequencing Consortium (IWGSC) chose a strategy that involves constructing bacterial artificial chromosome (BAC)-based physical maps of individual chromosomes and performing BAC-by-BAC sequencing. Here, we report the construction of a physical map of chromosome 6B with the goal of revealing the structural features of the third largest chromosome in wheat.

Results

We assembled 689 informative BAC contigs (hereafter reffered to as contigs) representing 91 % of the entire physical length of wheat chromosome 6B. The contigs were integrated into a radiation hybrid (RH) map of chromosome 6B, with one linkage group consisting of 448 loci with 653 markers. The order and direction of 480 contigs, corresponding to 87 % of the total length of 6B, were determined. We also characterized the contigs that contained a part of the nucleolus organizer region or centromere based on their positions on the RH map and the assembled BAC clone sequences. Analysis of the virtual gene order along 6B using the information collected for the integrated map revealed the presence of several chromosomal rearrangements, indicating evolutionary events that occurred on chromosome 6B.

Conclusions

We constructed a reliable physical map of chromosome 6B, enabling us to analyze its genomic structure and evolutionary progression. More importantly, the physical map should provide a high-quality and map-based reference sequence that will serve as a resource for wheat chromosome 6B.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1803-y) contains supplementary material, which is available to authorized users.

Chromosomal genomics facilitates fine mapping of a Russian wheat aphid resistance gene

Making use of wheat chromosomal resources, we developed 11 gene-associated markers for the region of interest, which allowed reducing gene interval and spanning it by four BAC clones. Positional gene cloning and targeted marker development in bread wheat are hampered by high complexity and polyploidy of its nuclear genome. Aiming to clone a Russian wheat aphid resistance gene Dn2401 located on wheat chromosome arm 7DS, we have developed a strategy overcoming problems due to polyploidy and enabling efficient development of gene-associated markers from the region of interest. We employed information gathered by GenomeZipper, a synteny-based tool combining sequence data of rice, Brachypodium, sorghum and barley, and took advantage of a high-density linkage map of Aegilops tauschii. To ensure genome- and locus-specificity of markers, we made use of survey sequence assemblies of isolated wheat chromosomes 7A, 7B and 7D. Despite the low level of polymorphism of the wheat D subgenome, our approach allowed us to add in an efficient and cost-effective manner 11 new gene-associated markers in the Dn2401 region and narrow down the target interval to 0.83 cM. Screening 7DS-specific BAC library with the flanking markers revealed a contig of four BAC clones that span the Dn2401 region in wheat cultivar 'Chinese Spring'. With the availability of sequence assemblies and GenomeZippers for each of the wheat chromosome arms, the proposed strategy can be applied for focused marker development in any region of the wheat genome.

The physical map of wheat chromosome 5DS revealed gene duplications and small rearrangements

BACKGROUND

The substantially large bread wheat genome, organized into highly similar three sub-genomes, renders genomic research challenging. The construction of BAC-based physical maps of individual chromosomes reduces the complexity of this allohexaploid genome, enables elucidation of gene space and evolutionary relationships, provides tools for map-based cloning, and serves as a framework for reference sequencing efforts. In this study, we constructed the first comprehensive physical map of wheat chromosome arm 5DS, thereby exploring its gene space organization and evolution.

RESULTS

The physical map of 5DS was comprised of 164 contigs, of which 45 were organized into 21 supercontigs, covering 176 Mb with an N50 value of 2,173 kb. Fifty-eight of the contigs were larger than 1 Mb, with the largest contig spanning 6,649 kb. A total of 1,864 molecular markers were assigned to the map at a density of 10.5 markers/Mb, anchoring 100 of the 120 contigs (>5 clones) that constitute ~95 % of the cumulative length of the map. Ordering of 80 contigs along the deletion bins of chromosome arm 5DS revealed small-scale breaks in syntenic blocks. Analysis of the gene space of 5DS suggested an increasing gradient of genes organized in islands towards the telomere, with the highest gene density of 5.17 genes/Mb in the 0.67-0.78 deletion bin, 1.4 to 1.6 times that of all other bins.

CONCLUSIONS

Here, we provide a chromosome-specific view into the organization and evolution of the D genome of bread wheat, in comparison to one of its ancestors, revealing recent genome rearrangements. The high-quality physical map constructed in this study paves the way for the assembly of a reference sequence, from which breeding efforts will greatly benefit.

New insights into the wheat chromosome 4D structure and virtual gene order, revealed by survey pyrosequencing

Survey sequencing of the bread wheat (Triticum aestivum L.) genome (AABBDD) has been approached through different strategies delivering important information. However, the current wheat sequence knowledge is not complete. The aim of our study is to provide different and complementary set of data for chromosome 4D. A survey sequence was obtained by pyrosequencing of flow-sorted 4DS (7.2×) and 4DL (4.1×) arms. Single ends (SE) and long mate pairs (LMP) reads were assembled into contigs (223Mb) and scaffolds (65Mb) that were aligned to Aegilops tauschii draft genome (DD), anchoring 34Mb to chromosome 4. Scaffolds annotation rendered 822 gene models. A virtual gene order comprising 1973 wheat orthologous gene loci and 381 wheat gene models was built. This order was largely consistent with the scaffold order determined based on a published high density map from the Ae. tauschii chromosome 4, using bin-mapped 4D ESTs as a common reference. The virtual order showed a higher collinearity with homeologous 4B compared to 4A. Additionally, a virtual map was constructed and ∼5700 genes (∼2200 on 4DS and ∼3500 on 4DL) predicted. The sequence and virtual order obtained here using the 454 platform were compared with the Illumina one used by the IWGSC, giving complementary information.

Major haplotype divergence including multiple germin-like protein genes, at the wheat Sr2 adult plant stem rust resistance locus

BACKGROUND

The adult plant stem rust resistance gene Sr2 was introgressed into hexaploid wheat cultivar (cv) Marquis from tetraploid emmer wheat cv Yaroslav, to generate stem rust resistant cv Hope in the 1920s. Subsequently, Sr2 has been widely deployed and has provided durable partial resistance to all known races of Puccinia graminis f. sp. tritici. This report describes the physical map of the Sr2-carrying region on the short arm of chromosome 3B of cv Hope and compares the Hope haplotype with non-Sr2 wheat cv Chinese Spring.

RESULTS

Sr2 was located to a region of 867 kb on chromosome 3B in Hope, which corresponded to a region of 567 kb in Chinese Spring. The Hope Sr2 region carried 34 putative genes but only 17 were annotated in the comparable region of Chinese Spring. The two haplotypes differed by extensive DNA sequence polymorphisms between flanking markers as well as by a major insertion/deletion event including ten Germin-Like Protein (GLP) genes in Hope that were absent in Chinese Spring. Haplotype analysis of a limited number of wheat genotypes of interest showed that all wheat genotypes carrying Sr2 possessed the GLP cluster; while, of those lacking Sr2, some, including Marquis, possessed the cluster, while some lacked it. Thus, this region represents a common presence-absence polymorphism in wheat, with presence of the cluster not correlated with presence of Sr2. Comparison of Hope and Marquis GLP genes on 3BS found no polymorphisms in the coding regions of the ten genes but several SNPs in the shared promoter of one divergently transcribed GLP gene pair and a single SNP downstream of the transcribed region of a second GLP.

CONCLUSION

Physical mapping and sequence comparison showed major haplotype divergence at the Sr2 locus between Hope and Chinese Spring. Candidate genes within the Sr2 region of Hope are being evaluated for the ability to confer stem rust resistance. Based on the detailed mapping and sequencing of the locus, we predict that Sr2 does not belong to the NB-LRR gene family and is not related to previously cloned, race non-specific rust resistance genes Lr34 and Yr36.

Next-generation sequencing of flow-sorted wheat chromosome 5D reveals lineage-specific translocations and widespread gene duplications

Background

The ~17 Gb hexaploid bread wheat genome is a high priority and a major technical challenge for genomic studies. In particular, the D sub-genome is relatively lacking in genetic diversity, making it both difficult to map genetically, and a target for introgression of agriculturally useful traits. Elucidating its sequence and structure will therefore facilitate wheat breeding and crop improvement.

Results

We generated shotgun sequences from each arm of flow-sorted Triticum aestivum chromosome 5D using 454 FLX Titanium technology, giving 1.34× and 1.61× coverage of the short (5DS) and long (5DL) arms of the chromosome respectively. By a combination of sequence similarity and assembly-based methods, ~74% of the sequence reads were classified as repetitive elements, and coding sequence models of 1314 (5DS) and 2975 (5DL) genes were generated. The order of conserved genes in syntenic regions of previously sequenced grass genomes were integrated with physical and genetic map positions of 518 wheat markers to establish a virtual gene order for chromosome 5D.

Conclusions

The virtual gene order revealed a large-scale chromosomal rearrangement in the peri-centromeric region of 5DL, and a concentration of non-syntenic genes in the telomeric region of 5DS. Although our data support the large-scale conservation of Triticeae chromosome structure, they also suggest that some regions are evolving rapidly through frequent gene duplications and translocations.

Sequence accessions

EBI European Nucleotide Archive, Study no. ERP002330

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1080) contains supplementary material, which is available to authorized users.

LTR retrotransposon dynamics in the evolution of the olive (Olea europaea) genome

Improved knowledge of genome composition, especially of its repetitive component, generates important information for both theoretical and applied research. The olive repetitive component is made up of two main classes of sequences: tandem repeats and retrotransposons (REs). In this study, we provide characterization of a sample of 254 unique full-length long terminal repeat (LTR) REs. In the sample, Ty1-Copia elements were more numerous than Ty3-Gypsy elements. Mapping a large set of Illumina whole-genome shotgun reads onto the identified retroelement set revealed that Gypsy elements are more redundant than Copia elements. The insertion time of intact retroelements was estimated based on sister LTR’s divergence. Although some elements inserted relatively recently, the mean insertion age of the isolated retroelements is around 18 million yrs. Gypsy and Copia retroelements showed different waves of transposition, with Gypsy elements especially active between 10 and 25 million yrs ago and nearly inactive in the last 7 million yrs. The occurrence of numerous solo-LTRs related to isolated full-length retroelements was ascertained for two Gypsy elements and one Copia element. Overall, the results reported in this study show that RE activity (both retrotransposition and DNA loss) has impacted the olive genome structure in more ancient times than in other angiosperms.

Whole-genome profiling and shotgun sequencing delivers an anchored, gene-decorated, physical map assembly of bread wheat chromosome 6A

Bread wheat (Triticum aestivum L.) is the most important staple food crop for 35% of the world's population. International efforts are underway to facilitate an increase in wheat production, of which the International Wheat Genome Sequencing Consortium (IWGSC) plays an important role. As part of this effort, we have developed a sequence-based physical map of wheat chromosome 6A using whole-genome profiling (WGP™). The bacterial artificial chromosome (BAC) contig assembly tools fingerprinted contig (fpc) and linear topological contig (ltc) were used and their contig assemblies were compared. A detailed investigation of the contigs structure revealed that ltc created a highly robust assembly compared with those formed by fpc. The ltc assemblies contained 1217 contigs for the short arm and 1113 contigs for the long arm, with an L50 of 1 Mb. To facilitate in silico anchoring, WGP™ tags underlying BAC contigs were extended by wheat and wheat progenitor genome sequence information. Sequence data were used for in silico anchoring against genetic markers with known sequences, of which almost 79% of the physical map could be anchored. Moreover, the assigned sequence information led to the 'decoration' of the respective physical map with 3359 anchored genes. Thus, this robust and genetically anchored physical map will serve as a framework for the sequencing of wheat chromosome 6A, and is of immediate use for map-based isolation of agronomically important genes/quantitative trait loci located on this chromosome.

Flow cytometric chromosome sorting from diploid progenitors of bread wheat, T. urartu, Ae. speltoides and Ae. tauschii

Chromosomes 5A (u) , 5S and 5D can be isolated from wild progenitors, providing a chromosome-based approach to develop tools for breeding and to study the genome evolution of wheat. The three subgenomes of hexaploid bread wheat originated from Triticum urartu (A(u)A(u)), from a species similar to Aegilops speltoides (SS) (progenitor of the B genome), and from Ae. tauschii (DD). Earlier studies indicated the potential of chromosome genomics to assist gene transfer from wild relatives of wheat and discover novel genes for wheat improvement. This study evaluates the potential of flow cytometric chromosome sorting in the diploid progenitors of bread wheat. Flow karyotypes obtained by analysing DAPI-stained chromosomes were characterized and the contents of the chromosome peaks were determined. FISH analysis with repetitive DNA probes proved that chromosomes 5A(u), 5S and 5D could be sorted with purities of 78-90 %, while the remaining chromosomes could be sorted in groups of three. Twenty-five conserved orthologous set (COS) markers covering wheat homoeologous chromosome groups 1-7 were used for PCR with DNA amplified from flow-sorted chromosomes and genomic DNA. These assays validated the cytomolecular results as follows: peak I on flow karyotypes contained chromosome groups 1, 4 and 6, peak II represented homoeologous group 5, while peak III consisted of groups 2, 3 and 7. The isolation of individual chromosomes of wild progenitors provides an attractive opportunity to investigate the structure and evolution of the polyploid genome and to deliver tools for wheat improvement.

A physical map of the short arm of wheat chromosome 1A

Bread wheat (Triticum aestivum) has a large and highly repetitive genome which poses major technical challenges for its study. To aid map-based cloning and future genome sequencing projects, we constructed a BAC-based physical map of the short arm of wheat chromosome 1A (1AS). From the assembly of 25,918 high information content (HICF) fingerprints from a 1AS-specific BAC library, 715 physical contigs were produced that cover almost 99% of the estimated size of the chromosome arm. The 3,414 BAC clones constituting the minimum tiling path were end-sequenced. Using a gene microarray containing ∼40 K NCBI UniGene EST clusters, PCR marker screening and BAC end sequences, we arranged 160 physical contigs (97 Mb or 35.3% of the chromosome arm) in a virtual order based on synteny with Brachypodium, rice and sorghum. BAC end sequences and information from microarray hybridisation was used to anchor 3.8 Mbp of Illumina sequences from flow-sorted chromosome 1AS to BAC contigs. Comparison of genetic and synteny-based physical maps indicated that ∼50% of all genetic recombination is confined to 14% of the physical length of the chromosome arm in the distal region. The 1AS physical map provides a framework for future genetic mapping projects as well as the basis for complete sequencing of chromosome arm 1AS.

Flow sorting and sequencing meadow fescue chromosome 4F

The analysis of large genomes is hampered by a high proportion of repetitive DNA, which makes the assembly of short sequence reads difficult. This is also the case in meadow fescue (Festuca pratensis), which is known for good abiotic stress resistance and has been used in intergeneric hybridization with ryegrasses (Lolium spp.) to produce Festulolium cultivars. In this work, we describe a new approach to analyze the large genome of meadow fescue, which involves the reduction of sample complexity without compromising information content. This is achieved by dissecting the genome to smaller parts: individual chromosomes and groups of chromosomes. As the first step, we flow sorted chromosome 4F and sequenced it by Illumina with approximately 50× coverage. This provided, to our knowledge, the first insight into the composition of the fescue genome, enabled the construction of the virtual gene order of the chromosome, and facilitated detailed comparative analysis with the sequenced genomes of rice (Oryza sativa), Brachypodium distachyon, sorghum (Sorghum bicolor), and barley (Hordeum vulgare). Using GenomeZipper, we were able to confirm the collinearity of chromosome 4F with barley chromosome 4H and the long arm of chromosome 5H. Several new tandem repeats were identified and physically mapped using fluorescence in situ hybridization. They were found as robust cytogenetic markers for karyotyping of meadow fescue and ryegrass species and their hybrids. The ability to purify chromosome 4F opens the way for more efficient analysis of genomic loci on this chromosome underlying important traits, including freezing tolerance. Our results confirm that next-generation sequencing of flow-sorted chromosomes enables an overview of chromosome structure and evolution at a resolution never achieved before.