High-throughput genotyping of wheat-barley amphiploids utilising diversity array technology (DArT)

Tritordeum: Creating a New Crop Species-The Successful Use of Plant Genetic Resources

Hexaploid tritordeum is the amphiploid derived from the cross between the wild barley Hordeum chilense and durum wheat. This paper reviews the main advances and achievements in the last two decades that led to the successful development of tritordeum as a new crop. In particular, we summarize the progress in breeding for agronomic performance, including the potential of tritordeum as a genetic bridge for wheat breeding; the impact of molecular markers in genetic studies and breeding; and the progress in quality and development of innovative food products. The success of tritordeum as a crop shows the importance of the effective utilization of plant genetic resources for the development of new innovative products for agriculture and industry. Considering that wild plant genetic resources have made possible the development of this new crop, the huge potential of more accessible resources, such as landraces conserved in gene banks, goes beyond being sources of resistance to biotic and abiotic stresses. In addition, the positive result of tritordeum also shows the importance of adequate commercialization strategies and demonstrative experiences aimed to integrate the whole food chain, from producers to end-point sellers, in order to develop new products for consumers.

Co-linearity and divergence of the A subgenome of Brassica juncea compared with other Brassica species carrying different A subgenomes

Background

There are three basic Brassica genomes (A, B, and C) and three parallel sets of subgenomes distinguished in the diploid Brassica (i.e.: B. rapa, A^rA^r; B. nigra, BⁿⁱBⁿⁱ; B. oleracea, C^oC^o) and the derived allotetraploid species (i.e.: B. juncea, A^jA^jB^jB^j; B. napus, AⁿAⁿCⁿCⁿ; B. carinata, B^cB^cC^cC^c). To understand subgenome differentiation in B. juncea in comparison to other A genome-carrying Brassica species (B. rapa and B. napus), we constructed a dense genetic linkage map of B. juncea, and conducted population genetic analysis on diverse lines of the three A-genome carrying Brassica species using a genotyping-by-sequencing approach (DArT-seq).

Results

A dense genetic linkage map of B. juncea was constructed using an F₂ population derived from Sichuan Yellow/Purple Mustard. The map included 3329 DArT-seq markers on 18 linkage groups and covered 1579 cM with an average density of two markers per cM. Based on this map and the alignment of the marker sequences with the physical genome of Arabidopsis thaliana, we observed strong co-linearity of the ancestral blocks among the different A subgenomes but also considerable block variation. Comparative analyses at the level of genome sequences of B. rapa and B. napus, and marker sequence anchored on the genetic map of B. juncea, revealed a total of 30 potential inversion events across large segments and 20 potential translocation events among the three A subgenomes. Population genetic analysis on 26 accessions of the three A genome-carrying Brassica species showed that the highest genetic distance were estimated when comparing A^j-Aⁿ than between Aⁿ-A^r and A^j-A^r subgenome pairs.

Conclusions

The development of the dense genetic linkage map of B. juncea with informative DArT-seq marker sequences and availability of the reference sequences of the A^r, and AⁿCⁿ genomes allowed us to compare the A subgenome structure of B. juncea (A^j) . Our results suggest that strong co-linearity exists among the three A Brassica genomes (A^r, Aⁿ and A^j) but with apparent subgenomic variation. Population genetic analysis on three A-genome carrying Brassica species support the idea that B. juncea has distinct genomic diversity, and/or evolved from a different A genome progenitor of B. napus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2343-1) contains supplementary material, which is available to authorized users.

DArT-based characterisation of genetic diversity in a Miscanthus collection from Poland

Analysis of 180 accessions of Miscanthus using a DArT platform revealed high diversity. The phylogenetic analysis revealed that M. × giganteus accessions fall into two genetically distinct groups. Miscanthus is a genus of perennial rhizomatous grasses that has emerged in last 20 years as a feedstock for bioenergy and biofuel production. Currently, the most widely used accession for bioenergy purposes is Miscanthus × giganteus, a sterile triploid hybrid between Miscanthus sinensis and Miscanthus sacchariflorus. However, previous reports have shown that genetic diversity of Miscanthus × giganteus is limited. Here, we report development of Diversity Arrays Technology platform for the analysis of genetic structure of a Miscanthus collection of 180 accessions. A total of 906 markers were obtained of which around 25.5% exhibited polymorphism information content value in the range of 0.40 and 0.50 and are considered particularly informative. Newly developed marker system will serve as an additional resource to assist crop improvement, germplasm preservation and genetic studies. Three types of analysis indicated that 180 accessions from the collection were well differentiated and presented high diversity. Interestingly, the analysis revealed that there are two separate groups of plants, significantly differing in genetic diversity, that are commercially available as M. × giganteus. We suggest that one of these groups is most likely mutants or somaclonal variants of original M. × giganteus. The other group is recent hybrids of Miscanthus of higher genetic diversity. This study indicates that the diversity of commercially available M. × giganteus is higher than commonly assumed. Development of the new marker system can significantly assist breeding of new commercial cultivars of Miscanthus for bioenergy use.

Fertility of CMS wheat is restored by two Rf loci located on a recombined acrocentric chromosome

Cytoplasmic male sterility (CMS) results from incompatibility between nuclear and cytoplasmic genomes, and is characterized by the inability to produce viable pollen. The restoration of male fertility generally involves the introgression of nuclear genes, termed restorers of fertility (Rf). CMS has been widely used for hybrid seed production in many crops but not in wheat, partly owing to the complex genetics of fertility restoration. In this study, an acrocentric chromosome that restores pollen fertility of CMS wheat in Hordeum chilense cytoplasm (msH1 system) is studied. The results show that this chromosome, of H. chilense origin and named H(ch)ac, originated from a complex reorganization of the short arm of chromosomes 1H(ch) (1H(ch)S) and 6H(ch) (6H(ch)S). Diversity arrays technology (DArT) markers and cytological analysis indicate that H(ch)ac is a kind of `zebra-like' chromosome composed of chromosome 1H(ch)S and alternate fragments of interstitial and distal regions of chromosome 6H(ch)S. PCR-based markers together with FISH, GISH, and meiotic pairing analysis support this result. A restorer of fertility gene, named Rf6H(ch)S, has been identified on the short arm of chromosome 6H(ch)S. Moreover, restoration by the addition of chromosome 1H(ch)S has been observed at a very low frequency and under certain environmental conditions. Therefore, the results indicate the presence of two Rf genes on the acrocentric chromosome: Rf6H(ch)S and Rf1H(ch)S, the restoration potential of Rf6H(ch)S being greater. The stable and high restoration of pollen fertility in the msH1 system is therefore the result of the interaction between these two restorer genes.

Potential of Start Codon Targeted (SCoT) markers for DNA fingerprinting of newly synthesized tritordeums and their respective parents

Hexaploid tritordeum (H(ch)H(ch)AABB; 2n = 42) results from the cross between Hordeum chilense (H(ch)H(ch); 2n = 14) and cultivated durum wheat (Triticum turgidum ssp. durum (AABB; 2n = 28). Morphologically, tritordeum resembles the wheat parent, showing promise for agriculture and wheat breeding. Start Codon Targeted (SCoT) polymorphism is a recently developed technique that generates gene-targeted markers. Thus, we considered it interesting to evaluate its potential for the DNA fingerprinting of newly synthesized hexaploid tritordeums and their respective parents. In this study, 60 SCoT primers were tested, and 18 and 19 of them revealed SCoT polymorphisms in the newly synthesized tritordeum lines HT27 and HT22, respectively, and their parents. An analysis of the presence/absence of bands among tritordeums and their parents revealed three types of polymorphic markers: (i) shared by tritordeums and one of their parents, (ii) exclusively amplified in tritordeums, and (iii) exclusively amplified in the parents. No polymorphism was detected among individuals of each parental species. Three SCoT markers were exclusively amplified in tritordeums of lines HT22 and HT27, being considered as polyploidization-induced rearrangements. About 70% of the SCoT markers of H. chilense origin were not transmitted to the allopolyploids of both lines, and most of the SCoTs scored in the newly synthesized allopolyploids originated from wheat, reinforcing the potential use of tritordeum as an alternative crop.

Phenolic content variability and its chromosome location in tritordeum

For humans, wheat is the most important source of calories, but it is also a source of antioxidant compounds that are involved in the prevention of chronic disease. Among the antioxidant compounds, phenolic acids have great potential to improve human health. In this paper we evaluate the effect of environmental and genetic factors on the phenolics content in the grain of a collection of tritordeums with different cytoplasm and chromosome substitutions. To this purpose, tritordeum flour was used for extraction of the free, conjugates and bound phenolic compounds. These phenolic compounds were identified and quantified by RP-HPLC and the results were analyzed by univariate and multivariate methods. This is the first study that describes the composition of phenolic acids of the amphiploid tritordeum. As in wheat, the predominant phenolic compound is ferulic acid. In tritordeum there is great variability for the content of phenolic compounds and the main factor which determines its content is the genotype followed by the environment, in this case included in the year factor. Phenolic acid content is associated with the substitution of chromosome DS1D(1H(ch)) and DS2D(2H(ch)), and the translocation 1RS/1BL in tritordeum. The results show that there is high potential for further improving the quality and quantity of phenolics in tritordeum because this amphiploid shows high variability for the content of phenolic compounds.