Diversity of grain proteins and bread wheat quality

Development and marker-trait relationships of functional markers for glutamine synthetase GS1 and GS2 homoeogenes in bread wheat

GS1 and GS2 genes encode, respectively, the main cytosolic and the plastidic isoforms of glutamine synthetase (GS). In the present study, the wheat GS1 and GS2 homoeogenes located in the A, B and D genome chromosomes have been sequenced in a group of 15 bread wheat varieties including landraces, old commercial varieties and modern cultivars. Phenotypic characterization by multi-environment field trials detected significant effects of specific GS homoeogenes on three of the seven agronomic and grain quality traits analyzed. Based on the gene sequence polymorphisms found, biallelic molecular markers that could facilitate marker-assisted breeding were developed for genes GS1A, GS2A and GS2D. The remaining genes encoding main wheat GS were excluded because of being monomorphic (GS1D) or too polymorphic (GS1B and GS2B) in the sequencing panel varieties. A collection of 187 Spanish bread wheat landraces was genotyped for these gene-based molecular markers. Data analyses conducted with phenotypic records reported for this germplasm collection in López-Fernández et al. (Plants-Basel 10: 620, 2021) have revealed the beneficial influence of some individual alleles on thousand-kernel weight (TKW), kernels per spike (KS) and grain protein content. Furthermore, genetic interactions between GS1A, a cytosolic GS isoform coding gene, and GS2A or GS2D, plastidic GS enzyme coding genes, were found to affect TKW and KS. The finding that some alleles at one locus may mask the effect of positive alleles at hypostatic GS loci should be kept in mind if gene pyramiding strategies are attempted for the improvement of N-use efficiency-related traits.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01354-0.

Increased Wheat Protein Content via Introgression of an HMW Glutenin Selectively Reshapes the Grain Proteome

Introgression of a high-molecular-weight glutenin subunit (HMW-GS) allele, 1Ay21∗, into commercial wheat cultivars increased overall grain protein content and bread-making quality, but the role of proteins beyond this HMW-GS itself was unknown. In addition to increased abundance of 1Ay HMW-GS, 115 differentially accumulated proteins (DAPs) were discovered between three cultivars and corresponding introgressed near-isogenic lines. Functional category analysis showed that the DAPs were predominantly other storage proteins and proteins involved in protein synthesis, protein folding, protein degradation, stress response, and grain development. Nearly half the genes encoding the DAPs showed strong coexpression patterns during grain development. Promoters of these genes are enriched in elements associated with transcription initiation and light response, indicating a potential connection between these cis-elements and grain protein accumulation. A model of how this HMW-GS enhances the abundance of machinery for protein synthesis and maturation during grain filling is proposed. This analysis not only provides insights into how introgression of the 1Ay21∗ improves grain protein content but also directs selection of protein candidates for future wheat quality breeding programs.

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Ay HMW-GS itself only contributes to 20% of the significant GPC increase in Ay NILs.

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Ay HMW-GS enhances other storage protein and protein synthesis machinery abundances.

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Expression of genes encoding Ay HMW-GS–induced proteins are strongly coexpressed.

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It provides a mechanistic model to influence future wheat quality breeding programs.

Effects of HMW-GSs on quality related traits in wheat (Triticum aestivum L.) under different water regimes

Alleles at the Glu-1 loci play important roles in the functional properties of wheat flour. The effects of various high-molecular-weight glutenin subunit (HMW-GS) compositions on quality traits and bread-making properties were evaluated using 235 doubled haploid lines (DHs). The experiment was conducted in a split plot design with two water regimes as the main plot treatment, and DH lines as the subplot treatments. Results showed that the presence of subunit pair 5+10 at the Glu-D1 locus, either alone or in combination with others, appears to provide an improvement in quality and bread-making properties. At the Glu-A1 locus, subunit 1 produced a higher Zeleny sedimentation value (Zel) and stretch area (SA) than subunit 2* when subunits 14+15 and 5+10 were expressed at the Glu-B1 and Glu-D1 loci, and 2* had a positive effect on the maximum dough resistance (Rmax) when subunits 14+15 and 5'+12 were expressed at the Glu-B1 and Glu-D1 loci, respectively. Given subunit 1 at the Glu-A1 locus and 5'+12 at the Glu-D1 locus, the effects of Glu-B1 subunits 14+15 on the tractility (Tra), dough stability time (ST), and dough development time (DT) under the well-watered regime were significantly higher than those of Glu-B1 subunits 13+16. However, 13+16 had a positive effect on SA under the rain-fed regime when subunits 2* and 5+10 were expressed at the Glu-A1 and Glu-D1 loci, respectively. Multiple comparisons analysis revealed that the Zel and Rmax of the six subunits and eight HMW-GS compositions were stable under different water regimes. Overall, subunit compositions 1, 13+16 and 5+10 and 1, 14+15 and 5+10 had higher values for quality traits and bread-baking properties under the two water regimes. These results could play a positive guiding role in selecting and popularizing varieties suitable for production and cultivation in local areas.

The thermal stability, structural changeability, and aggregability of glutenin and gliadin proteins induced by wheat bran dietary fiber

Wheat bran dietary fiber (WBDF) has been reported to be responsible for the low quality of whole wheat flour products due to its destructive effect on the gluten matrix. Glutenin and gliadin are the major components of gluten protein and contribute to a proper gluten structure. In this study, the thermostability, surface hydrophobicity, fluorescence characteristics, free sulfhydryl contents, and molecular weight distributions of glutenin- and gliadin-rich fractions were determined after the addition of WBDF. The addition of WBDF to glutenin resulted in an increased surface hydrophobicity and free sulfhydryl content, as well as a red-shift of the fluorescence spectrum. However, the WBDF-modified gliadin fraction changed slightly mainly due to its spherical conformation. Size exclusion chromatography profiles revealed increasing soluble gliadin aggregates and decreasing high molecular weight glutenin fractions as a result of WBDF incorporation. The results from the thermostability analyses exhibited decreased weight loss and decomposition temperatures for both glutenin and gliadin proteins at high WBDF concentration. Our results suggest that changes in the gluten matrix caused by WBDF may largely rely on glutenin structure variation.

Potential of Aegilops sp. for Improvement of Grain Processing and Nutritional Quality in Wheat (Triticum aestivum)

Wheat is one of the most important staple crops in the world and good source of calories and nutrition. Its flour and dough have unique physical properties and can be processed to make unique products like bread, cakes, biscuits, pasta, noodles etc., which is not possible from other staple crops. Due to domestication, the genetic variability of the genes coding for different economically important traits in wheat is narrow. This genetic variability can be increased by utilizing its wild relatives. Its closest relative, genus Aegilops can be an important source of new alleles. Aegilops has played a very important role in evolution of tetraploid and hexaploid wheat. It consists of 22 species with C, D, M, N, S, T and U genomes with high allelic diversity relative to wheat. Its utilization for wheat improvement for various abiotic and biotic stresses has been reported by various scientific publications. Here in, for the first time, we review the potential of Aegilops for improvement of processing and nutritional traits in wheat. Among processing quality related gluten proteins; high molecular weight glutenins (HMW GS), being easiest to study have been explored in highest number of accessions or lines i.e., 681 belonging to 13 species and selected ones like Ae. searsii, Ae. geniculata and Ae. longissima have been linked with improved bread making quality of wheat. Gliadins and low molecular weight glutenins (LMW GS) have also been extensively explored for wheat improvement and Ae. umbellulata specific LMW GS have been linked with wheat bread making quality improvement. Aegilops has been explored for seed texture diversity and proteins like puroindolins (Pin) and grain softness proteins (GSP). For nutrition quality improvement, it has been screened for essential micronutrients like Fe, Zn, phytochemicals like carotenoids and dietary fibers like arabinoxylan and β-glucan. Ae. kotschyi and Ae. biuncialis transfer in wheat have been associated with higher Fe, Zn content. In this article we have tried to compile information available on exploration of nutritional and processing quality related traits in Aegilops section and their utilization for wheat improvement by different approaches.

Developmental and physiological responses of Brachypodium distachyon to fluctuating nitrogen availability

The Nitrogen Use Efficiency (NUE) of grain cereals depends on nitrate (NO3-) uptake from the soil, translocation to the aerial parts, nitrogen (N) assimilation and remobilization to the grains. Brachypodium distachyon has been proposed as a model species to identify the molecular players and mechanisms that affects these processes, for the improvement of temperate C3 cereals. We report on the developmental, physiological and grain-characteristic responses of the Bd21-3 accession of Brachypodium to variations in NO3- availability. As previously described in wheat and barley, we show that vegetative growth, shoot/root ratio, tiller formation, spike development, tissue NO3- and N contents, grain number per plant, grain yield and grain N content are sensitive to pre- and/or post-anthesis NO3- supply. We subsequently described constitutive and NO3--inducible components of both High and Low Affinity Transport Systems (HATS and LATS) for root NO3- uptake, and BdNRT2/3 candidate genes potentially involved in the HATS. Taken together, our data validate Brachypodium Bd21-3 as a model to decipher cereal N nutrition. Apparent specificities such as high grain N content, strong post-anthesis NO3- uptake and efficient constitutive HATS, further identify Brachypodium as a direct source of knowledge for crop improvement.

Relationship of molecular weight distribution profile of unreduced gluten protein extracts with quality characteristics of bread

A statistical correlation was established among the molecular weight distribution patterns of unreduced gluten proteins and physicochemical, rheological and bread-making quality characteristics of wheat varieties. Size exclusion chromatography fractionated the gluten proteins apparently into five peaks. Peak I signified glutenins (30-130kDa), peak II as gliadins (20-55kDa), peak III as very low molecular weight monomeric gliadins (10-28kDa), peak IV and V, collectively, as albumins and globulins (<10kDa). Peaks I and II had appreciable effects on dough development time (r=0.830(∗∗) and r=-0.930(∗∗)) and dough stability (r=0.901(∗∗) and r=-0.979(∗∗)). Peak I was associated with R/E ratio (r=0.745(∗∗)), gluten index (r=0.959(∗∗)), and gliadin/glutenin ratio (r=-0.952(∗∗)), while peak II influenced inversely as expected. Peak I exhibited positive statistical significance with bread loaf volume (r=0.848(∗∗)); however, peak II had negative (r=-0.818(∗∗)) impact. Bread firmness increased with increment in peak II (r=0.625(∗∗)), and decreased with accretion in peak I (r=-0.623(∗∗)).

Biochemical and functional properties of wheat gliadins: a review

Gliadins account for 40-50% of the total storage proteins of wheat and are classified into four subcategories, α-, β-, γ-, and ω-gliadins. They have also been classified as ω5-, ω1, 2-, α/β-, and γ-gliadins on the basis of their primary structure and molecular weight. Cysteine residues of gliadins mainly form intramolecular disulfide bonds, although α-gliadins with odd numbers of cysteine residues have also been reported. Gliadins are generally regarded to possess globular protein structure, though recent studies report that the α/β-gliadins have compact globular structures and γ- and ω-gliadins have extended rod-like structures. Newer techniques such as Mass Spectrometry with the development of matrix-assisted laser desorption/ionization (MALDI) in combination with time-of-flight mass spectrometry (TOFMS) have been employed to determine the molecular weight of purified ω- gliadins and to carry out the direct analysis of bread and durum wheat gliadins. Few gliadin alleles and components, such as Gli-B1b, Gli-B2c and Gli-A2b in bread wheat cultivars, γ-45 in pasta, γ-gliadins in cookies, lower gliadin content for chapatti and alteration in Gli 2 loci in tortillas have been reported to improve the product quality, respectively. Further studies are needed in order to elucidate the precise role of gliadin subgroups in dough strength and product quality.

Genome-Wide Association Mapping of Yield and Grain Quality Traits in Winter Wheat Genotypes

The main goal of this study was to investigate the genetic basis of yield and grain quality traits in winter wheat genotypes using association mapping approach, and identify linked molecular markers for marker assisted selection. A total of 120 elite facultative/winter wheat genotypes were evaluated for yield, quality and other agronomic traits under rain-fed and irrigated conditions for two years (2011–2012) at the Tel Hadya station of ICARDA, Syria. The same genotypes were genotyped using 3,051 Diversity Array Technologies (DArT) markers, of which 1,586 were of known chromosome positions. The grain yield performance of the genotypes was highly significant both in rain-fed and irrigated sites. Average yield of the genotypes ranged from 2295 to 4038 kg/ha and 4268 to 7102 kg/ha under rain-fed and irrigated conditions, respectively. Protein content and alveograph strength (W) ranged from 13.6–16.1% and 217.6–375 Jx10-4, respectively. DArT markers wPt731910 (3B), wPt4680 (4A), wPt3509 (5A), wPt8183 (6B), and wPt0298 (2D) were significantly associated with yield under rain-fed conditions. Under irrigated condition, tPt4125 on chromosome 2B was significantly associated with yield explaining about 13% of the variation. Markers wPt2607 and wPt1482 on 5B were highly associated with protein content and alveograph strength explaining 16 and 14% of the variations, respectively. The elite genotypes have been distributed to many countries using ICARDA’s International system for potential direct release and/or use as parents after local adaptation trials by the NARSs of respective countries. The QTLs identified in this study are recommended to be used for marker assisted selection after through validation using bi-parental populations.

Diversity in quality traits amongst Indian wheat varieties I: flour and protein characteristics

The relationships of polymeric as well as monomeric proteins (unextractable and extractable) with various flour properties amongst Indian wheat varieties were evaluated. Unextractable polymeric proteins and unextractable monomeric proteins in flours ranged from 23.83% to 51.97% and 48.03% to 76.17%, respectively. Varieties with higher grain hardness index resulted into flours with higher a(∗), ash content and protein content. Unextractable polymeric and monomeric proteins were related to grain hardness index. Unextractable polymeric proteins showed a positive correlation with gluten index and LASRC. Majority of varieties with HMW-GS combinations of 91kDa+80kDa+78kDa+74kDa PPs showed very high grain hardness index (97-100).

Investigation of diversity in Aegilops biuncialis and Aegilops umbellulata by A-PAGE

Aegilops species, wild relatives of wheat, are one of the important genetic resources in wheat breeding. In this study 13 populations of Aegilops biuncialis along with 2 populations of progenitor species Aegilops umbellulata were analysed in six replications using of acid polyacrylamide gel electrophoresis. The results showed that TN-01-293 population had a high gluten and grind quality because of high percentage of γ-45.31 and γ-43.5 (high gluten quality index) in the observed band. Also, Ahar population from A. biuncialis was introduced to light gluten because of low percentage of γ-45.31 and γ-43.5 bands of quality. All studied populations can be used in breeding programmes for improving quality of bread wheat because of lack of γ-42 and γ-40 bands (low quality indices) and including high frequency of band in ω region. Through using PopGen 1.32 software, diversity is estimated . The maximum value of genetic diversity among populations resulted 49%.

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.

Fractionation of wheat gliadins by counter-current distribution using an organic two-phase system

A liquid liquid two-phase system based on N,N-dimethylformamide and the two polymers, poly(ethyleneglycol) and Ficoll, useful for partitioning of hydrophobic proteins, has been developed. The system has been applied to a counter-current distribution process in 56 steps for analysing the heterogeneity of proteins extracted with N,N-dimethylformamide from wheat flour. The counter-current distribution patterns of proteins, extracted from eight kinds of wheat, have been analysed. The minimum number of hypothetical proteins necessary to describe the patterns was found to be seven. The relative amount of these hypothetical components varied among the wheats.

Fractionation of wheat proteins by counter-current distribution using aqueous two-phase systems containing propionic acid

Wheat proteins, soluble in diluted acid (glutenins), have been fractionated by counter-current distribution (CCD) using an aqueous two-phase system. The phase system is based on poly(ethylene glycol) and dextran but contains also 1% propionic acid and 6 mM magnesium sulfate. Approximately half of the bulk proteins partitioned to the upper phase while starch and other particles were recovered only into the lower phase. Whole wheat flour could be applied as sample for the CCD and 57 transfers were carried out. Starch and insoluble proteins remained stationary, while proteins followed the mobile phase to various degrees giving rise to a distribution pattern. The CCD pattern of the proteins showed distinct differences when various kinds of wheat flour were analysed. The patterns indicate that at least six subpopulations of proteins can be obtained by using two-phase extraction.

From image processing to classification: IV. Classification of electrophoretic patterns by neural networks and statistical methods enable quality assessment of wheat varieties for breadmaking

The end-use quality of products made from doughs consisting of wheat flour and water is often dependent upon the storage (gluten) proteins of the grain endosperm. Today the electrophoretic patterns of the high molecular weight (HMW) glutenin subunits are used for quality selections in wheat breeding programs in several countries. In this study, we used two multivariate techniques to classify digitized patterns from isoelectric focusing of gliadins and glutenins: a two-layered neural network architecture consisting of a self-organizing feature map and a feed-forward classifier [1], and discriminant analysis [2,3]. Three groups of seven wheat varieties (Triticum aestivum L.), associated with poor, medium or good properties in relation to bread-making quality, were used. The best classification results were obtained by the neural network model, based on data from the gliadin fraction: it was possible to classify varieties associated with poor or good quality, with recognition rates of 70 and 69%, respectively. The statistical method was better suited to solve the classification problem when the data was based on the glutenin fraction: if a specific variety was already known to be non-poor, this method enabled us to classify the medium- and good-quality classes with recognition rates of 90 and 88%, respectively. The results obtained were confirmed by correlation coefficients.

Effect of gliadins and HMW and LMW subunits of glutenin on dough properties in the F6 recombinant inbred lines from a bread wheat cross

The storage proteins of 64 F2-derived F6 recombinant inbred lines (RILs) from the bread wheat cross 'Prinqual'/'Marengo' were analyzed. Parents differed at four loci: Gli-B1 (coding for gliadins), Glu-B1 (coding for HMW glutenin subunits), Glu-A3/Gli-A1 (coding for LMW glutenin subunits/gliadins) and Glu-D3 (coding for LMW glutenin subunits). The effect of allelic variation at these loci on tenacity, extensibility and dough strength as measured by the Chopin alveograph was determined. Allelic differences at the Glu-B1 locus had a significant effect on only tenacity. None of the allelic differences at either the Glu-A3/Gli-A1 or Glu-D3 loci had a significant effect on quality criteria. Allelic variation at the Gli-B1 locus significantly affected all of the dough properties. Epistatic effects between some of the loci considered contributed significantly to the variation in dough quality. Additive and epistatic effects each accounted for 15% of the variation in tenacity. Epistasis accounted for 15% of the variation in extensibility, whereas additive effects accounted for 4%. Epistasis accounted for 14% of the variation in dough strength, and additivity for 9%. The relative importance of epistatic effects suggest that they should be included in predictive models when breeding for breadmaking quality.

Genetic and environmental contributions to bread-wheat flour quality using the SDS sedimentation test as an index

The contribution of a locus to the genotypic variance depends not only on the effects of its genes but also on their frequency and on the genetic background in which it segregates. In two synthetic populations, involving common cultivars of our collection, estimates were made of the contributions of alleles at the homoeologous high-molecular-weight glutenin (HMW) loci, Glu-A1, Glu-B1, and Glu-D1, to the variation in flour quality using SDS sedimentation as an index. These estimates were of the magnitude of the contributions relative to each other, relative to the residual genetic variance, and relative to the environmental variance. The first population was a synthetic formed from ten bread-wheat cultivars known for their good quality, and selected under forced random mating for high SDS sedimentation. The second was the selfed progeny of a cross of Ribereño, a very poor quality bread-wheat of genotype (Null, 7-8,2-12), with line 7681, a very good quality bread-wheat with the genotype (2(*), 7-9, 5-10). Slightly over one-half of the phenotypic variance is under genetic control and over one-half of this was accounted for by HMW contributions. The initial response to selection was very rapid, as is expected when genes with large effects are involved. In addition, the frequencies of good HMW alleles increased so quickly that their contribution to the genetic variance was exhausted by the fourth generation of selection. If our estimates are correct, over one-half of the maximum possible advance in quality in heterogeneous populations similar to ours can easily be achieved in 2 years, or less, of marker-assisted selection.

Selection indices for quality evaluation in wheat breeding

From multilocation trials involving 125 cultivars of wheat of mainly French and European origin four tests - protein content, Pelshenke, modified Zeleny and the mixograph - were used to establish six selection indices. Three of these indices - IW1, IW2 and IW3 - were calculated in order to evaluate the genetic potentiality of the lines for dough strength as given by the Chopin alveograph. The indices IV1, IV2 and IV3 were established to evaluate loaf volume as measured by the French bread-making standard. A quality index IQ was calculated from the allelic effects of the high-molecular-weight (HMW) subunits of glutenin from 195 cultivars assessed by the Chopin alveograph and the Pelshenke test. Comparison of the relative efficiency of each of the six indices to the individual tests revealed the superiority of the indices over one or several technological parameters. The six selection indices and the quality index were compared using 30 very diverse F4 lines. Their ability to retain the good quality lines is discussed in particular.