The introgression of RNAi silencing of γ-gliadins into commercial lines of bread wheat changes the mixing and technological properties of the dough

Characterization of Glutenin Genes in Bread Wheat by Third-Generation RNA Sequencing and the Development of a Glu-1Dx5 Marker Specific for the Extra Cysteine Residue

High-molecular-weight glutenin subunits (HMW-GS) and low-molecular-weight glutenin subunits (LMW-GS) in a mature grain play important roles in the formation of a glutenin macropolymer and gluten quality. To characterize the expressed glutenin genes of the bread wheat variety Xinmai 26 during seed development, a total of 18 full-length transcripts were obtained by the newly emerged third-generation RNA sequencing of the PacBio Sequel II platform, including 5 transcripts of HMW-GS genes and 13 transcripts of LMW-GS genes (8 intact genes and 5 pseudogenes). Combined with the patterns of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), allelic types of the obtained glutenin genes were, respectively, determined, wherein molecular characterization deduced by transcript1528 (1Dx5) and transcript907 (Glu-A3c) indicated their great influence on dough quality. In addition, a specific functional marker dCAPS5 was developed for the single-nucleotide substitution at position 353 of the 1Dx5 subunit, which was further intensively compared with the other proposed markers to efficiently utilize the 1Dx5 subunit with the extra cysteine residue. This study provides an efficient method to accurately identify and utilize glutenin genes in bread wheat, which is helpful in understanding the contributions of glutenin genes to wheat quality.

Wheat Breeding, Fertilizers, and Pesticides: Do They Contribute to the Increasing Immunogenic Properties of Modern Wheat?

Celiac disease (CD) is a small intestinal inflammatory condition where consumption of gluten induces a T-cell mediated immune response that damages the intestinal mucosa in susceptible individuals. CD affects at least 1% of the world’s population. The increasing prevalence of CD has been reported over the last few decades. However, the reason for this increase is not known so far. Certain factors such as increase in awareness and the development of advanced and highly sensitive diagnostic screening markers are considered significant factors for this increase. Wheat breeding strategies, fertilizers, and pesticides, particularly herbicides, are also thought to have a role in the increasing prevalence. However, less is known about this issue. In this review, we investigated the role of these agronomic practices in depth. Our literature-based results showed that wheat breeding, use of nitrogen-based fertilizers, and herbicides cannot be solely responsible for the increase in celiac prevalence. However, applying nitrogen fertilizers is associated with an increase in gluten in wheat, which increases the risk of developing celiac-specific symptoms in gluten-sensitive individuals. Additionally, clustered regularly interspaced short palindromic repeats (CRISPR) techniques can edit multiple gliadin genes, resulting in a low-immunogenic wheat variety that is safe for such individuals.

Genome-Wide Identification, Characterization and Expression Pattern Analysis of the γ-Gliadin Gene Family in the Durum Wheat (Triticum durum Desf.) Cultivar Svevo

Very recently, the genome of the modern durum wheat cv. Svevo was fully sequenced, and its assembly is publicly available. So, we exploited the opportunity to carry out an in-depth study for the systematic characterization of the γ-gliadin gene family in the cv. Svevo by combining a bioinformatic approach with transcript and protein analysis. We found that the γ-gliadin family consists of nine genes that include seven functional genes and two pseudogenes. Three genes, Gli-γ1a, Gli-γ3a and Gli-γ4a, and the pseudogene Gli-γ2a* mapped on the A genome, whereas the remaining four genes, Gli-γ1b, Gli-γ2b, Gli-γ3b and Gli-γ5b, and the pseudogene Gli-γ4b* mapped on the B genome. The functional γ-gliadins presented all six domains and eight-cysteine residues typical of γ-gliadins. The Gli-γ1b also presented an additional cysteine that could possibly have a role in the formation of the gluten network through binding to HMW glutenins. The γ-gliadins from the A and B genome differed in their celiac disease (CD) epitope content and composition, with the γ-gliadins from the B genome showing the highest frequency of CD epitopes. In all the cases, almost all the CD epitopes clustered in the central region of the γ-gliadin proteins. Transcript analysis during seed development revealed that all the functional γ-gliadin genes were expressed with a similar pattern, although significant differences in the transcript levels were observed among individual genes that were sometimes more than 60-fold. A progressive accumulation of the γ-gliadin fraction was observed in the ripening seeds that reached 34% of the total gliadin fraction at harvest maturity. We believe that the insights generated in the present study could aid further studies on gliadin protein functions and future breeding programs aimed at the selection of new healthier durum wheat genotypes.

Breeding Canola (Brassica napus L.) for Protein in Feed and Food

Interest in canola (Brassica napus L.). In response to this interest, scientists have been tasked with altering and optimizing the protein production chain to ensure canola proteins are safe for consumption and economical to produce. Specifically, the role of plant breeders in developing suitable varieties with the necessary protein profiles is crucial to this interdisciplinary endeavour. In this article, we aim to provide an overarching review of the canola protein chain from the perspective of a plant breeder, spanning from the genetic regulation of seed storage proteins in the crop to advancements of novel breeding technologies and their application in improving protein quality in canola. A review on the current uses of canola meal in animal husbandry is presented to underscore potential limitations for the consumption of canola meal in mammals. General discussions on the allergenic potential of canola proteins and the regulation of novel food products are provided to highlight some of the challenges that will be encountered on the road to commercialization and general acceptance of canola protein as a dietary protein source.

The MYB family transcription factor TuODORANT1 from Triticum urartu and the homolog TaODORANT1 from Triticum aestivum inhibit seed storage protein synthesis in wheat

Seed storage proteins (SSPs) are determinants of wheat end-product quality. SSP synthesis is mainly regulated at the transcriptional level. Few transcriptional regulators of SSP synthesis have been identified in wheat and this study aims to identify novel SSP gene regulators. Here, the R2R3 MYB transcription factor TuODORANT1 from Triticum urartu was found to be preferentially expressed in the developing endosperm during grain filling. In common wheat (Triticum aestivum) overexpressing TuODORANT1, the transcription levels of all the SSP genes tested by RNA-Seq analysis were reduced by 49.71% throughout grain filling, which contributed to 13.38%-35.60% declines in the total SSP levels of mature grains. In in vitro assays, TuODORANT1 inhibited both the promoter activities and the transcription of SSP genes by 1- to 13-fold. The electrophoretic mobility shift assay (EMSA) and ChIP-qPCR analysis demonstrated that TuODORANT1 bound to the cis-elements 5'-T/CAACCA-3' and 5'-T/CAACT/AG-3' in SSP gene promoters both in vitro and in vivo. Similarly, the homolog TaODORANT1 in common wheat hindered both the promoter activities and the transcription of SSP genes by 1- to 112-fold in vitro. Knockdown of TaODORANT1 in common wheat led to 14.73%-232.78% increases in the transcription of the tested SSP genes, which contributed to 11.43%-19.35% elevation in the total SSP levels. Our data show that both TuODORANT1 and TaODORANT1 are repressors of SSP synthesis.

The endosperm-specific transcription factor TaNAC019 regulates glutenin and starch accumulation and its elite allele improves wheat grain quality

In wheat (Triticum aestivum L.), breeding efforts have focused intensively on improving grain yield and quality. For quality, the content and composition of seed storage proteins (SSPs) determine the elasticity of wheat dough and flour processing quality. Moreover, starch levels in seeds are associated with yield. However, little is known about the mechanisms that coordinate SSP and starch accumulation in wheat. In this study, we explored the role of the endosperm-specific NAC transcription factor TaNAC019 in coordinating SSP and starch accumulation. TaNAC019 binds to the promoters of TaGlu-1 loci, encoding high molecular weight glutenin (HMW-GS), and of starch metabolism genes. Triple knock-out mutants of all three TaNAC019 homoeologs exhibited reduced transcript levels for all SSP types and genes involved in starch metabolism, leading to lower gluten and starch contents, and in flour processing quality parameters. TaNAC019 directly activated the expression of HMW-GS genes by binding to a specific motif in their promoters and interacting with the TaGlu-1 regulator TaGAMyb. TaNAC019 also indirectly regulated the expression of TaSPA, an ortholog of maize Opaque2 that activates SSP accumulation. Therefore, TaNAC019 regulation of starch- and SSP-related genes has key roles in wheat grain quality. Finally, we identified an elite allele (TaNAC019-BI) associated with flour processing quality, providing a candidate gene for breeding wheat with improved quality.

A novel NAC family transcription factor SPR suppresses seed storage protein synthesis in wheat

The synthesis of seed storage protein (SSP) is mainly regulated at the transcriptional level. However, few transcriptional regulators of SSP synthesis have been characterized in common wheat (Triticum aestivum) owing to the complex genome. As the A genome donor of common wheat, Triticum urartu could be an elite model in wheat research considering its simple genome. Here, a novel NAC family transcription factor TuSPR from T. urartu was found preferentially expressed in developing endosperm during grain-filling stages. In common wheat transgenically overexpressing TuSPR, the content of total SSPs was reduced by c. 15.97% attributed to the transcription declines of SSP genes. Both in vitro and in vivo assays showed that TuSPR bound to the cis-element 5'-CANNTG-3' distributed in SSP gene promoters and suppressed the transcription. The homolog in common wheat TaSPR shared a conserved function with TuSPR on SSP synthesis suppression. The knock-down of TaSPR in common wheat resulted in 7.07%-20.34% increases in the total SSPs. Both TuSPR and TaSPR could be superior targets in genetic engineering to manipulate SSP content in wheat, and this work undoubtedly expands our knowledge of SSP gene regulation.

Genomic and functional genomics analyses of gluten proteins and prospect for simultaneous improvement of end-use and health-related traits in wheat

KEY MESSAGE

Recent genomic and functional genomics analyses have substantially improved the understanding on gluten proteins, which are important determinants of wheat grain quality traits. The new insights obtained and the availability of precise, versatile and high-throughput genome editing technologies will accelerate simultaneous improvement of wheat end-use and health-related traits. Being a major staple food crop in the world, wheat provides an indispensable source of dietary energy and nutrients to the human population. As worldwide population grows and living standards rise in both developed and developing countries, the demand for wheat with high quality attributes increases globally. However, efficient breeding of high-quality wheat depends on critically the knowledge on gluten proteins, which mainly include several families of prolamin proteins specifically accumulated in the endospermic tissues of grains. Although gluten proteins have been studied for many decades, efficient manipulation of these proteins for simultaneous enhancement of end-use and health-related traits has been difficult because of high complexities in their expression, function and genetic variation. However, recent genomic and functional genomics analyses have substantially improved the understanding on gluten proteins. Therefore, the main objective of this review is to summarize the genomic and functional genomics information obtained in the last 10 years on gluten protein chromosome loci and genes and the cis- and trans-factors regulating their expression in the grains, as well as the efforts in elucidating the involvement of gluten proteins in several wheat sensitivities affecting genetically susceptible human individuals. The new insights gathered, plus the availability of precise, versatile and high-throughput genome editing technologies, promise to speed up the concurrent improvement of wheat end-use and health-related traits and the development of high-quality cultivars for different consumption needs.

Prolamin Content and Grain Weight in RNAi Silenced Wheat Lines Under Different Conditions of Temperature and Nitrogen Availability

Temperature and nitrogen (N) availability are two important environmental factors that may produce important changes in grain composition during grain filling of bread wheat. In this study, four wheat lines with the down-regulation of gliadins by means of RNA interference (RNAi) have been characterized to determine the effect of thermal stress and N availability on grain weight and quality; with focus on gliadin and glutenin protein fractions. Grain weight was reduced with heat stress (HS) in all RNAi lines, whereas gliadin content was increased in the wild-types. With respect to gliadin content, RNAi lines responded to HS and N availability differently from their respective wild-types, except for ω-gliadin content, indicating a very clear stability of silencing under different environmental conditions. In a context of increased temperature and HS events, and in environments with different N availability, the RNAi lines with down-regulated gliadins seem well suited for the production of wheat grain with low gliadin content.

Wheat Seed Proteins: Factors Influencing Their Content, Composition, and Technological Properties, and Strategies to Reduce Adverse Reactions

Wheat is the primary source of nutrition for many, especially those living in developing countries, and wheat proteins are among the most widely consumed dietary proteins in the world. However, concerns about disorders related to the consumption of wheat and/or wheat gluten proteins have increased sharply in the last 20 years. This review focuses on wheat gluten proteins and amylase trypsin inhibitors, which are considered to be responsible for eliciting most of the intestinal and extraintestinal symptoms experienced by susceptible individuals. Although several approaches have been proposed to reduce the exposure to gluten or immunogenic peptides resulting from its digestion, none have proven sufficiently effective for general use in coeliac-safe diets. Potential approaches to manipulate the content, composition, and technological properties of wheat proteins are therefore discussed, as well as the effects of using gluten isolates in various food systems. Finally, some aspects of the use of gluten-free commodities are discussed.

Genetic Modification for Wheat Improvement: From Transgenesis to Genome Editing

To feed the growing human population, global wheat yields should increase to approximately 5 tonnes per ha from the current 3.3 tonnes by 2050. To reach this goal, existing breeding practices must be complemented with new techniques built upon recent gains from wheat genome sequencing, and the accumulated knowledge of genetic determinants underlying the agricultural traits responsible for crop yield and quality. In this review we primarily focus on the tools and techniques available for accessing gene functions which lead to clear phenotypes in wheat. We provide a view of the development of wheat transformation techniques from a historical perspective, and summarize how techniques have been adapted to obtain gain-of-function phenotypes by gene overexpression, loss-of-function phenotypes by expressing antisense RNAs (RNA interference or RNAi), and most recently the manipulation of gene structure and expression using site-specific nucleases, such as CRISPR/Cas9, for genome editing. The review summarizes recent successes in the application of wheat genetic manipulation to increase yield, improve nutritional and health-promoting qualities in wheat, and enhance the crop's resistance to various biotic and abiotic stresses.

Plant Proteases: From Key Enzymes in Germination to Allies for Fighting Human Gluten-Related Disorders

Plant proteases play a crucial role in many different biological processes along the plant life cycle. One of the most determinant stages in which proteases are key protagonists is the plant germination through the hydrolysis and mobilization of other proteins accumulated in seeds and cereal grains. The most represented proteases in charge of this are the cysteine proteases group, including the C1A family known as papain-like and the C13 family also called legumains. In cereal species such as wheat, oat or rye, gluten is a very complex mixture of grain storage proteins, which may affect the health of sensitive consumers like celiac patients. Since gluten proteins are suitable targets for plant proteases, the knowledge of the proteases involved in storage protein mobilization could be employed to manipulate the amount of gluten in the grain. Some proteases have been previously found to exhibit promising properties for their application in the degradation of known toxic peptides from gluten. To explore the variability in gluten-degrading capacities, we have now analyzed the degradation of gluten from different wheat cultivars using several cysteine proteases from barley. The wide variability showed highlights the possibility to select the protease with the highest potential to alter grain composition reducing the gluten content. Consequently, new avenues could be explored combining genetic manipulation of proteolytic processes with silencing techniques to be used as biotechnological tools against gluten-related disorders.

Gluten-Free Products for Celiac Susceptible People

The gluten protein of wheat triggers an immunological reaction in some gluten-sensitive people with HLA-DQ2/8 genotypes, which leads to Celiac disease (CD) with symptomatic damage in the small intestinal villi. Glutenin and gliadin are two major components of gluten that are essentially required for developing a strong protein network for providing desired viscoelasticity of dough. Many non-gluten cereals and starches (rice, corn, sorghum, millets, and potato/pea starch) and various gluten replacers (xanthan and guar gum) have been used for retaining the physical-sensorial properties of gluten-free, cereal-based products. This paper reviews the recent advances in the formulation of cereal-based, gluten-free products by utilizing alternate flours, starches, gums, hydrocolloids, enzymes, novel ingredients, and processing techniques. The pseudo cereals amaranth, quinoa, and buckwheat, are promising in gluten-free diet formulation. Genetically-modified wheat is another promising area of research, where successful attempts have been made to silence the gliadin gene of wheat using RNAi techniques. The requirement of quantity and quality for gluten-free packaged foods is increasing consistently at a faster rate than lactose-free and diabetic-friendly foods. More research needs to be focused on cereal-based, gluten-free beverages to provide additional options for CD sufferers.

Gluten Immunogenic Peptides as Standard for the Evaluation of Potential Harmful Prolamin Content in Food and Human Specimen

Gluten is a complex mixture of storage proteins in cereals like wheat, barley, and rye. Prolamins are the main components of gluten. Their high content in proline and glutamine makes them water-insoluble and difficult to digest in the gastrointestinal tract. Partial digestion generates peptide sequences which trigger immune responses in celiac and gluten-sensitive patients. Gluten detection in food is challenging because of the diversity, in various food matrices, of protein proportions or modifications and the huge number of immunogenic sequences with differential potential immunoactivity. Attempts to develop standard reference materials have been unsuccessful. Recent studies have reported the detection of a limited number of dominant Gluten Immunogenic Peptides (GIP) that share similarities to epitopes presented in the α-gliadin 33-mer, which showed to be highly proteolytic resistant and is considered to be the most immunodominant peptide within gluten in celiac disease (CD). GIP were detectable and quantifiable in very different kind of difficult to analyze food, revealing the potential immunogenicity by detecting T-cell activity of celiac patients. But GIP were also found in stool and urine of celiac patients on a supposedly gluten-free diet (GFD), showing the capacity to resist and be absorbed and excreted from the body, providing the first simple and objective means to assess adherence to the GFD. Methods to specifically and sensitively detect the most active GIP in food and biological fluids are rational candidates may use similar analytical standard references for determination of the immunopathological risk of gluten exposure in gluten-related diseases.

Genome mapping of seed-borne allergens and immunoresponsive proteins in wheat

Wheat is an important staple grain for humankind globally because of its end-use quality and nutritional properties and its adaptability to diverse climates. For a small proportion of the population, specific wheat proteins can trigger adverse immune responses and clinical manifestations such as celiac disease, wheat allergy, baker's asthma, and wheat-dependent exercise-induced anaphylaxis (WDEIA). Establishing the content and distribution of the immunostimulatory regions in wheat has been hampered by the complexity of the wheat genome and the lack of complete genome sequence information. We provide novel insights into the wheat grain proteins based on a comprehensive analysis and annotation of the wheat prolamin Pfam clan grain proteins and other non-prolamin allergens implicated in these disorders using the new International Wheat Genome Sequencing Consortium bread wheat reference genome sequence, RefSeq v1.0. Celiac disease and WDEIA genes are primarily expressed in the starchy endosperm and show wide variation in protein- and transcript-level expression in response to temperature stress. Nonspecific lipid transfer proteins and α-amylase trypsin inhibitor gene families, implicated in baker's asthma, are primarily expressed in the aleurone layer and transfer cells of grains and are more sensitive to cold temperature. The study establishes a new reference map for immunostimulatory wheat proteins and provides a fresh basis for selecting wheat lines and developing diagnostics for products with more favorable consumer attributes.

Analysis of the Gli-D2 locus identifies a genetic target for simultaneously improving the breadmaking and health-related traits of common wheat

Gliadins are a major component of wheat seed proteins. However, the complex homoeologous Gli-2 loci (Gli-A2, -B2 and -D2) that encode the α-gliadins in commercial wheat are still poorly understood. Here we analyzed the Gli-D2 locus of Xiaoyan 81 (Xy81), a winter wheat cultivar. A total of 421.091 kb of the Gli-D2 sequence was assembled from sequencing multiple bacterial artificial clones, and 10 α-gliadin genes were annotated. Comparative genomic analysis showed that Xy81 carried only eight of the α-gliadin genes of the D genome donor Aegilops tauschii, with two of them each experiencing a tandem duplication. A mutant line lacking Gli-D2 (DLGliD2) consistently exhibited better breadmaking quality and dough functionalities than its progenitor Xy81, but without penalties in other agronomic traits. It also had an elevated lysine content in the grains. Transcriptome analysis verified the lack of Gli-D2 α-gliadin gene expression in DLGliD2. Furthermore, the transcript and protein levels of protein disulfide isomerase were both upregulated in DLGliD2 grains. Consistent with this finding, DLGliD2 had increased disulfide content in the flour. Our work sheds light on the structure and function of Gli-D2 in commercial wheat, and suggests that the removal of Gli-D2 and the gliadins specified by it is likely to be useful for simultaneously enhancing the end-use and health-related traits of common wheat. Because gliadins and homologous proteins are widely present in grass species, the strategy and information reported here may be broadly useful for improving the quality traits of diverse cereal crops.

Food processing and breeding strategies for coeliac-safe and healthy wheat products

A strict gluten-free diet is currently the only treatment for the 1-2% of the world population who suffer from coeliac disease (CD). However, due to the presence of wheat and wheat derivatives in many food products, avoiding gluten consumption is difficult. Gluten-free products, made without wheat, barley or rye, typically require the inclusion of numerous additives, resulting in products that are often less healthy than gluten-based equivalents. Here, we present and discuss two broad approaches to decrease wheat gluten immunogenicity for CD patients. The first approach is based on food processing strategies, which aim to remove gliadins or all gluten from edible products. We find that several of the candidate food processing techniques to produce low gluten-immunogenic products from wheat already exist. The second approach focuses on wheat breeding strategies to remove immunogenic epitopes from the gluten proteins, while maintaining their food-processing properties. A combination of breeding strategies, including mutation breeding and possibly genome editing, will be necessary to produce coeliac-safe wheat. Individuals suffering from CD and people genetically susceptible who may develop CD after prolonged gluten consumption would benefit from reduced CD-immunogenic wheat. Although the production of healthy and less CD-toxic wheat varieties and food products will be challenging, increasing global demand may require these issues to be addressed in the near future by food processing and cereal breeding companies.

Novel insights into the effect of nitrogen on storage protein biosynthesis and protein body development in wheat caryopsis

Molecular and cytological mechanisms concerning the effects of nitrogen on wheat (Triticum aestivum L.) storage protein biosynthesis and protein body development remain largely elusive. We used transcriptome sequencing, proteomics techniques, and light microscopy to investigate these issues. In total, 2585 differentially expressed genes (DEGs) and 57 differentially expressed proteins (DEPs) were found 7 days after anthesis (DAA), and 2456 DEGs and 64 DEPs were detected 18 DAA after nitrogen treatment. Gene ontology terms related to protein biosynthesis processes enriched these numbers by 678 and 582 DEGs at 7 and 18 DAA, respectively. Further, 25 Kyoto Encyclopedia of Genes and Genomes pathways were involved in protein biosynthesis at both 7 and 18 DAA. DEPs related to storage protein biosynthesis contained gliadin and glutenin subunits, most of which were up-regulated after nitrogen treatment. Quantitative real-time PCR analysis indicated that some gliadin and glutenin subunit encoding genes were differentially expressed at 18 DAA. Structural observation revealed that wheat endosperm accumulated more and larger protein bodies after nitrogen treatment. Collectively, our findings suggest that nitrogen treatment enhances storage protein content, endosperm protein body quantity, and partial processing quality by altering the expression levels of certain genes involved in protein biosynthesis pathways and storage protein expression at the proteomics level.

Physiopathology and Management of Gluten-Induced Celiac Disease

Proline- and glutamine-rich gluten proteins are one of the major constituents of cereal dietary proteins, which are largely resistant to complete cleavage by the human gastrointestinal (GI) digestive enzymes. Partial digestion of gluten generates approximately 35 amino acids (aa) immunomodulatory peptides which activate T-cell-mediated immune system, followed by immunological inflammation of mucosa leading to the onset of celiac disease (CD). CD is an autoimmune disease associated with HLA-DQ2/DQ8 polymorphism and dysbiosis of gut microbiota. CD is either diagnosed using duodenal mucosal biopsis or serological testing for transglutaminase 2 (TG2) specific antibodies (IgA and IgG). Current therapy for CD management is gluten-free diet, while other therapies like glutenase, probiotics, immunomodulation, jamming of HLA-DQ2, inhibition of TG2, and gluten tolerance aided by gluten tolerizing vaccines are being developed.

Targeting of prolamins by RNAi in bread wheat: effectiveness of seven silencing-fragment combinations for obtaining lines devoid of coeliac disease epitopes from highly immunogenic gliadins

Gluten proteins are responsible for the viscoelastic properties of wheat flour but also for triggering pathologies in susceptible individuals, of which coeliac disease (CD) and noncoeliac gluten sensitivity may affect up to 8% of the population. The only effective treatment for affected persons is a strict gluten-free diet. Here, we report the effectiveness of seven plasmid combinations, encompassing RNAi fragments from α-, γ-, ω-gliadins, and LMW glutenin subunits, for silencing the expression of different prolamin fractions. Silencing patterns of transgenic lines were analysed by gel electrophoresis, RP-HPLC and mass spectrometry (LC-MS/MS), whereas gluten immunogenicity was assayed by an anti-gliadin 33-mer monoclonal antibody (moAb). Plasmid combinations 1 and 2 downregulated only γ- and α-gliadins, respectively. Four plasmid combinations were highly effective in the silencing of ω-gliadins and γ-gliadins, and three of these also silenced α-gliadins. HMW glutenins were upregulated in all but one plasmid combination, while LMW glutenins were downregulated in three plasmid combinations. Total protein and starch contents were unaffected regardless of the plasmid combination used. Six plasmid combinations provided strong reduction in the gluten content as measured by moAb and for two combinations, this reduction was higher than 90% in comparison with the wild type. CD epitope analysis in peptides identified in LC-MS/MS showed that lines from three plasmid combinations were totally devoid of CD epitopes from the highly immunogenic α- and ω-gliadins. Our findings raise the prospect of breeding wheat species with low levels of harmful gluten, and of achieving the important goal of developing nontoxic wheat cultivars.

Improving wheat to remove coeliac epitopes but retain functionality

Coeliac disease is an intolerance triggered by the ingestion of wheat gluten proteins. It is of increasing concern to consumers and health professionals as its incidence appears to be increasing. The amino acid sequences in gluten proteins that are responsible for triggering responses in sensitive individuals have been identified showing that they vary in distribution among and between different groups of gluten proteins. Conventional breeding may therefore be used to select for gluten protein fractions with lower contents of coeliac epitopes. Molecular breeding approaches can also be used to specifically down-regulate coeliac-toxic proteins or mutate coeliac epitopes within individual proteins. A combination of these approaches may therefore be used to develop a “coeliac-safe” wheat. However, this remains a formidable challenge due to the complex multigenic control of gluten protein composition. Furthermore, any modified wheats must retain acceptable properties for making bread and other processed foods. Not surprisingly, such coeliac-safe wheats have not yet been developed despite over a decade of research.

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Coeliac disease is of increasing concern as its incidence appears to be increasing.

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Over 30 amino acid sequences (coeliac epitopes) have been defined.

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Coeliac epitopes differ in their distribution between wheat gluten proteins.

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Transgenesis can be used to reduce coeliac-toxic proteins and coeliac epitopes.

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This can be exploited to develop “coeliac-safe” wheats.

Silencing of omega-5 gliadins in transgenic wheat eliminates a major source of environmental variability and improves dough mixing properties of flour

BACKGROUND

The end-use quality of wheat flour varies as a result of the growth conditions of the plant. Among the wheat gluten proteins, the omega-5 gliadins have been identified as a major source of environmental variability, increasing in proportion in grain from plants that receive fertilizer or are subjected to high temperatures during grain development. The omega-5 gliadins also have been associated with the food allergy wheat-dependent exercise-induced anaphylaxis (WDEIA). Recently, transgenic lines with reduced levels of omega-5 gliadins were developed using RNA interference (RNAi). These lines make it possible to determine whether changes in the levels of omega-5 gliadins in response to environmental conditions and agronomic inputs may be responsible for changes in flour end-use quality.

RESULTS

Two transgenic wheat lines and a non-transgenic control were grown under a controlled temperature regimen with or without post-anthesis fertilizer and the protein composition of the resulting flour was analyzed by quantitative two-dimensional gel electrophoresis (2-DE). In one transgenic line, all 2-DE spots identified as omega-5 gliadins were substantially reduced without effects on other proteins. In the other transgenic line, the omega-5 gliadins were absent and there was a partial reduction in the levels of the omega-1,2 gliadins and the omega-1,2 chain-terminating gliadins as well as small changes in several other proteins. With the exception of the omega gliadins, the non-transgenic control and the transgenic plants showed similar responses to the fertilizer treatment. Protein contents of flour were determined by the fertilizer regimen and were similar in control and transgenic samples produced under each regimen while both mixing time and mixing tolerance were improved in flour from transgenic lines when plants received post-anthesis fertilizer.

CONCLUSIONS

The data indicate that omega-5 gliadins have a negative effect on flour quality and suggest that changes in quality with the growth environment may be due in part to alterations in the levels of the omega gliadins. Because a known food allergen and one of the major sources of environmentally-induced variation in wheat flour protein composition has been eliminated, the transgenic lines may yield flour with both improved end-use quality and more consistent functionality when grown in different locations.

The shutdown of celiac disease-related gliadin epitopes in bread wheat by RNAi provides flours with increased stability and better tolerance to over-mixing

Celiac disease is a food-sensitive enteropathy triggered by the ingestion of wheat gluten proteins and related proteins from barley, rye, and some varieties of oat. There are no interventional therapies and the only solution is a lifelong gluten-free diet. The down-regulation of gliadins by RNAi provides wheat lines with all the gliadin fractions strongly down-regulated (low-gliadin). The technological properties of doughs prepared from the low-gliadin lines indicated a general weakening effect, although some of the lines displayed similar properties to that of the wild-type lines. In contrast, the stability was increased significantly in some of the transgenic lines, indicating better tolerance to over-mixing. Results reported here are the first analyses of the mixing and bread-making quality of the wheat lines with all gliadin fractions strongly down-regulated. Flour from these lines may be an important breakthrough in the development of new products for the celiac community. These lines might be used directly or blended with other non-toxic cereals, as raw material for developing food products that can be safely tolerated by CD patients and others with gluten intolerance or gluten sensitivity, incrementing the range of available food products and enhancing their diet.

Efficient isolation of ion beam-induced mutants for homoeologous loci in common wheat and comparison of the contributions of Glu-1 loci to gluten functionality

Ion beam mutations can be efficiently isolated and deployed for functional comparison of homoeologous loci in polyploid plants, and Glu - 1 loci differ substantially in their contribution to wheat gluten functionality. To efficiently conduct genetic analysis, it is beneficial to have multiple types of mutants for the genes under investigation. Here, we demonstrate that ion beam-induced deletion mutants can be efficiently isolated for comparing the function of homoeologous loci of common wheat (Triticum aestivum). Through fragment analysis of PCR products from M2 plants, ion beam mutants lacking homoeologous Glu-A1, Glu-B1 or Glu-D1 loci, which encode high molecular weight glutenin subunits (HMW-GSs) and affect gluten functionality and end-use quality of common wheat, could be isolated simultaneously. Three deletion lines missing Glu-A1, Glu-B1 or Glu-D1 were developed from the original mutants, with the Glu-1 genomic regions deleted in these lines estimated using newly developed DNA markers. Apart from lacking the target HMW-GSs, the three lines all showed decreased accumulation of low molecular weight glutenin subunits (LMW-GSs) and increased amounts of gliadins. Based on the test data of five gluten and glutenin macropolymer (GMP) parameters obtained with grain samples harvested from two environments, we conclude that the genetic effects of Glu-1 loci on gluten functionality can be ranked as Glu-D1 > Glu-B1 > Glu-A1. Furthermore, it is suggested that Glu-1 loci contribute to gluten functionality both directly (by promoting the formation of GMP) and indirectly (through keeping the balance among HMW-GSs, LMW-GSs and gliadins). Finally, the efficient isolation of ion beam mutations for functional comparison of homoeologous loci in polyploid plants and the usefulness of Glu-1 deletion lines for further studying the contribution of Glu-1 loci to gluten functionality are discussed.

Efficient isolation of ion beam-induced mutants for homoeologous loci in common wheat and comparison of the contributions of Glu-1 loci to gluten functionality

Ion beam mutations can be efficiently isolated and deployed for functional comparison of homoeologous loci in polyploid plants, and Glu - 1 loci differ substantially in their contribution to wheat gluten functionality. To efficiently conduct genetic analysis, it is beneficial to have multiple types of mutants for the genes under investigation. Here, we demonstrate that ion beam-induced deletion mutants can be efficiently isolated for comparing the function of homoeologous loci of common wheat (Triticum aestivum). Through fragment analysis of PCR products from M2 plants, ion beam mutants lacking homoeologous Glu-A1, Glu-B1 or Glu-D1 loci, which encode high molecular weight glutenin subunits (HMW-GSs) and affect gluten functionality and end-use quality of common wheat, could be isolated simultaneously. Three deletion lines missing Glu-A1, Glu-B1 or Glu-D1 were developed from the original mutants, with the Glu-1 genomic regions deleted in these lines estimated using newly developed DNA markers. Apart from lacking the target HMW-GSs, the three lines all showed decreased accumulation of low molecular weight glutenin subunits (LMW-GSs) and increased amounts of gliadins. Based on the test data of five gluten and glutenin macropolymer (GMP) parameters obtained with grain samples harvested from two environments, we conclude that the genetic effects of Glu-1 loci on gluten functionality can be ranked as Glu-D1 > Glu-B1 > Glu-A1. Furthermore, it is suggested that Glu-1 loci contribute to gluten functionality both directly (by promoting the formation of GMP) and indirectly (through keeping the balance among HMW-GSs, LMW-GSs and gliadins). Finally, the efficient isolation of ion beam mutations for functional comparison of homoeologous loci in polyploid plants and the usefulness of Glu-1 deletion lines for further studying the contribution of Glu-1 loci to gluten functionality are discussed.

The tip of the "celiac iceberg" in China: a systematic review and meta-analysis

Objective

Until recently, celiac disease was considered to be rare in China. We aimed to estimate its true status.

Methods

By searching the MEDLINE database and four Chinese full-text databases (CNKI, CBM, VIP and WANFANG) (up to August 2012), as well as two HLA allele frequency net databases and the Chinese Statistics Yearbook databases, we systematically reviewed the literature on definite and suspected cases of celiac disease, the predisposing HLA allele frequencies, and on gluten exposure in China. Meta-analysis was performed by analyzing DQ2, DQ8 and DQB1*0201 gene frequencies and heterogeneity in populations from different geographic regions and ethnicities in China.

Results

At present, the number of reported celiac disease cases is extremely low in China. The frequencies of the HLA-DQ2.5 and HLA-DQ8 haplotypes were 3.4% (95% confidence interval 1.3–5.5%) and 2.1% (0.1–4.1%), respectively. HLA-DQ2 and HLA-DQ8 antigen frequencies were 18.4% (15.0–21.7%) and 8.0% (4.5–11.4%), respectively. The frequency of the DQB1*0201 allele was 10.5% (9.3–11.6%) and it was more common in the northern Chinese than in the southern Chinese populations. The chance of being exposed to gluten is rapidly increasing all over China nowadays.

Conclusion

The data on HLA haplotyping, in conjunction with increasing wheat consumption, strongly suggests that the occurrence of celiac disease is more common in China than currently reported. Coordinated measures by the Chinese government, medical and agricultural research institutions, and food industries, would be justified to create more awareness about celiac disease and to prevent it becoming a medical and societal burden.

Expansion of the gamma-gliadin gene family in Aegilops and Triticum

BACKGROUND

The gamma-gliadins are considered to be the oldest of the gliadin family of storage proteins in Aegilops/Triticum. However, the expansion of this multigene family has not been studied in an evolutionary perspective.

RESULTS

We have cloned 59 gamma-gliadin genes from Aegilops and Triticum species (Aegilops caudata L., Aegilops comosa Sm. in Sibth. & Sm., Aegilops mutica Boiss., Aegilops speltoides Tausch, Aegilops tauschii Coss., Aegilops umbellulata Zhuk., Aegilops uniaristata Vis., and Triticum monococcum L.) representing eight different genomes: Am, B/S, C, D, M, N, T and U. Overall, 15% of the sequences contained internal stop codons resulting in pseudogenes, but this percentage was variable among genomes, up to over 50% in Ae. umbellulata. The most common length of the deduced protein, including the signal peptide, was 302 amino acids, but the length varied from 215 to 362 amino acids, both obtained from Ae. speltoides. Most genes encoded proteins with eight cysteines. However, all Aegilops species had genes that encoded a gamma-gliadin protein of 302 amino acids with an additional cysteine. These conserved nine-cysteine gamma-gliadins may perform a specific function, possibly as chain terminators in gluten network formation in protein bodies during endosperm development. A phylogenetic analysis of gamma-gliadins derived from Aegilops and Triticum species and the related genera Lophopyrum, Crithopsis, and Dasypyrum showed six groups of genes. Most Aegilops species contained gamma-gliadin genes from several of these groups, which also included sequences from the genera Lophopyrum, Crithopsis, and Dasypyrum. Hordein and secalin sequences formed separate groups.

CONCLUSIONS

We present a model for the evolution of the gamma-gliadins from which we deduce that the most recent common ancestor (MRCA) of Aegilops/Triticum-Dasypyrum-Lophopyrum-Crithopsis already had four groups of gamma-gliadin sequences, presumably the result of two rounds of duplication of the locus.