Hordeum chilense genome, a useful tool to investigate the endosperm yellow pigment content in the Triticeae

Marker-Trait Associations for Total Carotenoid Content and Individual Carotenoids in Durum Wheat Identified by Genome-Wide Association Analysis

Yellow pigment content is one of the main traits considered for grain quality in durum wheat (Triticum turgidum L.). The yellow color is mostly determined by carotenoid pigments, lutein being the most abundant in wheat endosperm, although zeaxanthin, α-carotene and β-carotene are present in minor quantities. Due to the importance of carotenoids in human health and grain quality, modifying the carotenoid content and profile has been a classic target. Landraces are then a potential source for the variability needed for wheat breeding. In this work, 158 accessions of the Spanish durum wheat collection were characterized for carotenoid content and profile and genotyped using the DArTSeq platform for association analysis. A total of 28 marker-trait associations were identified and their co-location with previously described QTLs and candidate genes was studied. The results obtained confirm the importance of the widely described QTL in 7B and validate the QTL regions recently identified by haplotype analysis for the semolina pigment. Additionally, copies of the Zds and Psy genes on chromosomes 7B and 5B, respectively, may have a putative role in determining zeaxanthin content. Finally, genes for the methylerythritol 4-phosphate (MEP) and isopentenyl diphosphate (IPPI) carotenoid precursor pathways were revealed as additional sources of untapped variation for carotenoid improvement.

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.

Mediation of a GDSL Esterase/Lipase in Carotenoid Esterification in Tritordeum Suggests a Common Mechanism of Carotenoid Esterification in Triticeae Species

Carotenoids are essential in human diet, so that the development of programs toward carotenoid enhancement has been promoted in several crops. The cereal tritordeum, the amphiploid derived from the cross between Hordeum chilense Roem. et Schulz. and durum wheat has a remarkable carotenoid content in the endosperm. Besides, a high proportion of these carotenoids are esterified with fatty acids. The identification of the gene(s) responsible for xanthophyll esterification would be useful for breeding as esterified carotenoids show an increased ability to accumulate within plant cells and have a higher stability during post-harvest storage. In this work, we analyzed five genes identified as candidates for coding the xanthophyll acyltransferase (XAT) enzyme responsible for lutein esterification in H. chilense genome. All these genes were expressed during grain development in tritordeum, but only HORCH7HG021460 was highly upregulated. Sequence analysis of HORCH7HG021460 revealed a G-to-T transversion, causing a Glycine to Cysteine substitution in the protein of H290 (the only accession not producing quantifiable amounts of lutein esters, hereinafter referred as zero-ester) of H. chilense compared to the esterifying genotypes. An allele-specific marker was designed for the SNP detection in the H. chilense diversity panel. From the 93 accessions, only H290 showed the T allele and the zero-ester phenotype. Furthermore, HORCH7HG021460 is the orthologue of XAT-7D, which encodes a XAT enzyme responsible for carotenoid esterification in wheat. Thus, HORCH7HG021460 (XAT-7Hch) is a strong candidate for lutein esterification in H. chilense and tritordeum, suggesting a common mechanism of carotenoid esterification in Triticeae species. The transference of XAT-7Hch to wheat may be useful for the enhancement of lutein esters in biofortification programs.

Lutein ester profile in wheat and tritordeum can be modulated by temperature: Evidences for regioselectivity and fatty acid preferential of enzymes encoded by genes on chromosomes 7D and 7Hch

The increase of lutein retention through the food chain is desirable for wheat breeding. Lutein esters are more stable than free lutein during post-harvest storage and two loci on chromosomes 7D and 7H^ch are important for esterification. We investigated the effect of temperature during grain filling on carotenoid accumulation and lutein ester profile including fatty acid selectivity (palmitic vs. linoleic) and regioselectivity (esterification at positions 3 vs. 3'). Three different temperature regimes were assayed (controlled, semi-controlled and non-controlled). Lutein esters were more stable than free carotenoids in vivo and the enzymes encoded by chromosomes 7H^ch and 7D are complementary. Indeed, they show differential preferences for the fatty acid (palmitic and linoleic, respectively) and regioselectivity (3 and 3', respectively). Besides, H. chilense has additional genes for esterification. Finally, the increase of temperature favoured the accumulation of lutein esters with linoleic acid and the synthesis of regioisomers at position 3'.

Fine mapping of barley locus Rps6 conferring resistance to wheat stripe rust

KEY MESSAGE

Barley resistance to wheat stripe rust has remained effective for a long time and, therefore, the genes underlying this resistance can be a valuable tool to engineer durable resistance in wheat. Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a major disease of wheat that is causing large economic losses in many wheat-growing regions of the world. Deployment of Pst resistance genes has been an effective strategy for controlling this pathogen, but many of these genes have been defeated by new Pst races. In contrast, genes providing resistance to this wheat pathogen in other grass species (nonhost resistance) have been more durable. Barley varieties (Hordeum vulgare ssp. vulgare) are predominately immune to wheat Pst, but we identified three accessions of wild barley (Hordeum vulgare ssp. spontaneum) that are susceptible to Pst. Using these accessions, we mapped a barley locus conferring resistance to Pst on the distal region of chromosome arm 7HL and designated it as Rps6. The detection of the same locus in the cultivated barley 'Tamalpais' and in the Chinese barley 'Y12' by an allelism test suggests that Rps6 may be a frequent component of barley intermediate host resistance to Pst. Using a high-density mapping population (>10,000 gametes) we precisely mapped Rps6 within a 0.14 cM region (~500 kb contig) that is colinear to regions in Brachypodium (<94 kb) and rice (<9 kb). Since no strong candidate gene was identified in these colinear regions, a dedicated positional cloning effort in barley will be required to identify Rps6. The identification of this and other barley genes conferring resistance to Pst can contribute to our understanding of the mechanisms for durable resistance against this devastating wheat pathogen.

Novel Bread Wheat Lines Enriched in Carotenoids Carrying Hordeum chilense Chromosome Arms in the ph1b Background

The use of crop wild relative species to improve major crops performance is well established. Hordeum chilense has a high potential as a genetic donor to increase the carotenoid content of wheat. Crosses between the 7H^chH. chilense substitution lines in wheat and the wheat pairing homoeologous1b (ph1b) mutant allowed the development of wheat-H. chilense translocation lines for both 7H^chα and 7H^chβ chromosome arms in the wheat background. These translocation lines were characterized by in situ hybridization and using molecular markers. In addition, reverse phase chromatography (HPLC) analysis was carried out to evaluate the carotenoid content and both 7H^chα∙7AL and 7AS∙7H^chβ disomic translocation lines. The carotenoid content in 7H^chα∙7AL and 7AS∙7H^chβ disomic translocation lines was higher than the wheat-7H^ch addition line and double amount of carotenoids than the wheat itself. A proteomic analysis confirmed that the presence of chromosome 7H^ch introgressions in wheat scarcely altered the proteomic profile of the wheat flour. The Psy1 (Phytoene Synthase1) gene, which is the first committed step in the carotenoid biosynthetic pathway, was also cytogenetically mapped on the 7H^chα chromosome arm. These new wheat-H. chilense translocation lines can be used as a powerful tool in wheat breeding programs to enrich the diet in bioactive compounds.

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.

Increase in transcript accumulation of Psy1 and e-Lcy genes in grain development is associated with differences in seed carotenoid content between durum wheat and tritordeum

Carotenoid rich diets have been associated with lower risk of certain diseases. The great importance of cereals in human diet has directed breeding programs towards carotenoid enhancement to alleviate these deficiencies in developing countries and to offer new functional foods in the developed ones. The new cereal tritordeum (×Tritordeum Ascherson et Graebener) derived from durum wheat (Triticum turgidum ssp. durum) and the wild barley Hordeum chilense, naturally presents carotenoid levels 5-8 times higher than those of durum wheat. The improvement of tritordeum properties as a new functional food requires the elucidation of biosynthetic steps for carotenoid accumulation in seeds that differ from durum wheat. In this work expression patterns of nine genes from the isoprenoid and carotenoid biosynthetic pathways were monitored during grain development in durum wheat and tritordeum. Additionally, a fine identification and quantification of pigments (chlorophylls and carotenoids) during grain development and in mature seeds has been addressed. Transcript levels of Psy1, Psy2, Zds, e-Lcy and b-Lcy were found to correlate to carotenoid content in mature grains. The specific activation of the homeologous genes Psy1, e-Lcy from H. chilense and the high lutein esterification found in tritordeum may serve to explain the differences with durum wheat in carotenoid accumulation.