Breeding for increased grain protein and micronutrient content in wheat: Ten years of the GPC-B1 gene

To provide food and nutrition security for a growing world population, continued improvements in the yield and nutritional quality of agricultural crops will be required. Wheat is an important source of calories, protein and micronutrients and is thus a priority to breed for improvements in these traits. The GRAIN PROTEIN CONTENT-B1 (GPC-B1) gene is a positive regulator of nutrient translocation which increases protein, iron and zinc concentration in the wheat grain. In the ten years since it was cloned, the impacts of GPC-B1 allelic variation on quality and yield traits have been extensively analyzed in diverse genetic backgrounds in field studies spanning forty environments and seven countries. In this review, we compile data from twenty-five studies to summarize the impact of GPC-B1 allelic variation on fifty different traits. Taken together, the results demonstrate that the functional copy of the GPC-B1 gene is associated with consistent positive effects on grain protein, Fe and Zn content with only marginally negative impacts on yield. We conclude that the GPC-B1 gene has the potential to increase nutritional and end use quality in a wide range of modern cultivars and environments and discuss the possibilities for its application in wheat breeding.     

Vitreosity,its stability and relationship to protein content in durum wheat

High quality requirements are set on durum wheat (Triticum durum) from semolina mills and pasta producers. For the production of semolina and pasta with good cooking quality, high grain protein content and vitreosity is required. The dependency of vitreosity on protein content as well as its stability under the influence of humidity was not well investigated up to now. We (1) compared two methods to determine vitreosity, (2) investigated the relationship between vitreosity and protein content, (3) developed a method to analyze vitreosity under humidity, and (4) examined the relationship between protein content and agronomical as well as quality traits in durum wheat. The results showed that the formation of vitreous kernels greatly depends on the protein content. To evaluate the stability of vitreosity under the influence of humidity a new method was elaborated and employed to assess the durum germplasm under study. This revealed that vitreosity of a durum wheat variety depends on the potential to form vitreous kernels but also to maintain this vitreosity under the influence of humidity. Our results further show that protein content is a central trait in durum wheat that strongly influences important traits like grain yield, vitreosity, and b-value.     

Influence of the cultivar,environment and management on the grain yield and bread-making quality in winter wheat

The genotype, environment and their interaction play an important role in the grain yielding and grain quality attributes. The main aim of this study was to determine the contributions of the genotype, environment and their interaction to the variation in bread-making traits. The data that were used for the analyses performed in this study were obtained from 3 locations in Poland from post-registration multi-environment trials with winter wheat in 2009 and 2010. The experimental factors were the cultivar (7 cultivars) and the crop management level (low input and high input). In the multi-environment trials, 17 traits were investigated that characterize grain, flour and dough quality. Most of the traits were affected much more strongly by environmental factors (i.e., year and location) than by genotype. The variance components revealed an especially strong effect of the year on the baking score, loaf volume and water absorption, as well a strong effect of the location on dough development and protein content. The obtained results demonstrate that the grain quality as measured by the parameters based on the protein content and quality may be substantially improved by crop management practices, especially by N fertilization level.     

Combined mutations in five wheat STARCH BRANCHING ENZYME II genes improve resistant starch but affect grain yield and bread-making quality

Increases in the proportion of amylose in the starch of wheat grains result in higher levels of resistant starch, a fermentable dietary fiber associated with human health benefits. The objective of this study was to assess the effect of combined mutations in five STARCH BRANCHING ENZYME II (SBEII) genes on starch composition, grain yield and bread-making quality in two hexaploid wheat varieties. Significantly higher amylose (∼60%) and resistant starch content (10-fold) was detected in the SBEII mutants than in the wild-type controls. Mutant lines showed a significant decrease in total starch (6%), kernel weight (3%) and total grain yield (6%). Effects of the mutations in bread-making quality included increases in grain hardness, starch damage, water absorption and flour protein content; and reductions in flour extraction, farinograph development and stability times, starch viscosity, and loaf volume. Several traits showed significant interactions between genotypes, varieties, and environments, suggesting that some of the negative impacts of the combined SBEII mutations can be ameliorated by adequate selection of genetic background and growing location. The deployment of wheat varieties with increased resistant starch will likely require economic incentives to compensate growers and millers for the significant reductions detected in grain and flour yields.     

The impact of Septoria tritici blotch in bread making quality among argentinean wheat cultivars

Septoria tritici blotch (STB), caused by Zymoseptoria tritici is a relevant foliar wheat disease worldwide. Several reports show the importance of STB on grain yield, their components and grain protein while little is known about its effect on the rheological properties of the wheat flour. The scarce literature found, only mentions the effect of the complex of foliar diseases on wheat quality, without individualizing the effect of the different pathogens separately. This study analyze the influence of increasing doses of inoculum of Zymoseptoria tritici, on the bread making quality of ten Argentinean wheat cultivars and its possible variation according to their quality group. The increase of inoculum concentration augmented the area under disease progress curve, decreased green flag leaf area duration and green leaf area duration. Cultivars K. Flecha and B.75 Aniversario had the lowest green flag leaf area duration causing higher reduction in grain filling period and higher reductions in P, indicating a lower gliadin/glutenin ratio. STB decreased P/L and E while L, W, D, SV and bread volume increased. Cultivars differed in rheological parameters according to their quality group. Gluten/protein relationship was significant in quality group 1 and non-significant in cultivars belonging to quality group 2 and 3.     

Kernel vitreousness and protein content: Relationship,interaction and synergistic effects on durum wheat quality

Four sets of durum samples were used in this study to further understand the interrelationships among hard vitreous kernels (HVK), protein content, and pigment concentration, with a focus on the interaction and synergistic effects of protein content and vitreousness on durum quality. HVK level increases with higher protein content in the range of 9.5–12.5%, but this relationship is less evident in durum samples with high protein content (12.5–14.5%). Both protein content and kernel vitreousness can significantly affect durum milling quality. White starchy kernels (WSK) in low protein durum have a very detrimental impact on milling and pasta processing quality, but high protein content can mitigate the adverse impact of WSK on durum quality. Although protein content plays a dominant role, higher HVK might contribute positively to pasta firmness. There was no significant difference in yellow pigment content between HVK and WSK. However, pigment loss from semolina to dough was higher for WSK than HVK. Despite the difference in protein content, HVK and WSK have little difference in gluten strength. The monomeric protein was preferentially accumulated in HVK. The glutenin proteins of HVK and WSK were similar in the ratios of 1Bx/1By and HMW/LMW-GS.     

Molecular characterization of storage proteins for selected durum wheat varieties grown in different environments

The variations of the amounts of individual high molecular weight glutenin subunits (HMW-GS), of the ratios HMW-GSy to HMW-GSx and HMW-GS to low molecular weight glutenin subunits (LMW-GS) and of protein content were evaluated for eight durum wheat cultivars in two regions using four fertilizer combinations during two successive years. All measured parameters showed significant variation with genotypes (G), environments (E) and fertilizers (F). The interaction E × G × F was highly significant for glutenin amount variation. Amongst cultivars possessing HMW-GS 20, landraces seem to better value the N-fertilizer use for the accumulation of HMW-GSy than high yielding cultivars. Both HMW-GSy to HMW-GSx and HMW-GS to LMW-GS ratios were found to be positively correlated (p < 0.05) with total protein content.     

Modification of protein structure and dough rheological properties of wheat flour through superheated steam treatment

Native (NF, 13.5% w.b) and moistened (MF, 27% w.b) wheat flours were treated with superheated steam (SS) at 170 °C for 1, 2 and 4 min, and their protein structure as well as dough rheological properties were analyzed. Confocal laser scanning microscopy (CLSM) and SDS-PAGE patterns indicated the formation of protein aggregates with reduced SDS extractability after treatment. Farinograph and dynamic rheometry measurements showed that the strength as well as elastic and viscous moduli of the dough made from SS-treated flours progressively increased with SS treatment time. And both the improvements were more pronounced for superheated steam-treated moistened flours (SS-MF) than for superheated steam-treated native flours (SS-NF). Size-exclusion high performance liquid chromatography (SE-HPLC) analysis demonstrated that dough rheological parameters have positive correlations with SDS unextractable polymeric proteins (UPP) contents. SS treatment on flours led to a transition of protein secondary structures to more ordered form (α-helix and β-sheet). Additionally, free sulfhydryl (SH) contents decreased after treatment, which implied that disulfide bonds accounted for protein extractability loss and dough rheological properties improvement. Elevated moisture level promoted the modification of both protein structure and dough behaviors of flours during SS treatment.     

Metabolite profiling of the response to high-nitrogen fertilizer during grain development of bread wheat (Triticum aestivum L.)

Wheat yield and quality are dependent largely on nitrogen (N) availability. In this study, we performed the first metabolomic analysis of the response to high-N fertilizer during wheat grain development using non-targeted gas chromatography-mass spectrometry (GC–MS). Quality parameter analyses demonstrated that high-N fertilizer application led to a significant increase in grain protein content and improvement in starch and bread-making quality. Comparative metabolomic profiling of six grain developmental stages resulted in identification of 74 metabolites, including amino acids, carbohydrates, organic acids and lipids/alcohol, which are primarily involved in carbon and N metabolism. Under high-N fertilizer treatment, numerous metabolites accumulated significantly during grain development. Principal component analysis revealed two principal components as being responsible for the variances resulting from N-fertilizer treatments. Metabolite–metabolite correlation analysis demonstrated that the high-N treatment group had a greater number of positive correlations among metabolites, suggesting that high-N fertilizer treatment induced a concerted metabolic change that resulted in improved grain development. Particularly, the high-N treatment-mediated significant accumulation of metabolites involved in the TCA cycle, starch and storage protein synthesis could be responsible for the improvement of grain yield and quality. Our results provide new insight into the molecular mechanisms of wheat grain development and yield and quality.     

Polymerisation of gluten proteins in developing wheat grain as affected by desiccation

The breadmaking quality of wheat is affected by the composition of gluten proteins and the polymerisation of subunits that are synthesised and accumulated in developing wheat grain. The biological mechanisms and time course of these events during grain development are documented, but not widely confirmed. Therefore, the aim of this study was to monitor the accumulation of gluten protein subunits and the size distribution of protein aggregates during grain development. The effect of desiccation on the polymerisation of gluten proteins and the functional properties of gluten were also studied. The results showed that the size of glutenin polymers remained consistently low until yellow ripeness (YR), while it increased during grain desiccation after YR. Hence, this polymerisation process was presumed to be initiated by desiccation. A similar polymerisation event was also observed when premature grains were dried artificially. The composition of gluten proteins, the ratios of glutenin to gliadin and high molecular weight-glutenin subunits to low molecular weight-glutenin subunits, in premature grain after artificial desiccation showed close association with the size of glutenin polymers in artificially dried grain. Functional properties of gluten in these samples were also associated with polymer size after artificial desiccation.     

Variation in gluten quality parameters of spring wheat varieties of different origin grown in contrasting environments

The aim of this study was to investigate variation in protein content and gluten viscoelastic properties in wheat genotypes grown in two mega-environments of contrasting climates: the southeast of Norway and Minnesota, USA. Twelve spring wheat varieties, nine from Norway and three HRS from Minnesota, were grown in field experiments at different locations in Norway and Minnesota during 2009–2011. The results showed higher protein content but lower TW and TKW when plants were grown in Minnesota, while the gluten quality measured as Rmax showed large variation between locations in both mega-environments. On average, Rmax of the samples grown in Minnesota was higher than those grown in Norway, but some locations in Norway had similar Rmax values to locations in Minnesota. The data showed inconsistent relationship between the temperature during grain filling and Rmax. Our results suggest that the weakening effect of low temperatures on gluten reported in this study are caused by other environmental factors that relate to low temperatures. The variety Berserk showed higher stability in Rmax as it obtained higher values in the environments in Norway that gave very weak gluten for other varieties.     

Immunomodulatory activities of non-prolamin proteins in wheat germ and gluten

Albumin (Alb), globulin (Glo), glutelin (Gll) and glutenin (Gln) were separately extracted from wheat germ and wheat gluten. Amino acisd composition, molecular weight distribution, solubility, in vitro digestibility, and immunomodulatory activities were all analyzed. Gll and Gln have similar molecular weight distributions, which differed from those of Alb and Glo. Alb showed the highest solubility at various pH values (except pH 4.0), whereas Glo showed the highest in vitro digestibility. Glo and Gll have the highest proportion of essential to total amino acids, while Alb and Gll have the highest protein digestibility-corrected amino acid scores. Gll had the strongest immunomodulatory effects in terms of stimulation of RAW 264.7 cells to produce IL-6, TNF-α, and IL-10, and good stimulatory effects on splenocyte proliferation, production of IL-2, phagocytosis, and secretion of nitric oxide in RAW 264.7 cells. Gll can be considered a good protein source for use in health foods.     

Antioxidant properties of wheat and rye bran extracts obtained by pressurized liquid extraction with different solvents

Rye and wheat brans are valuable sources of bioactive compounds, which could be used for the development and commercialization of high added value functional ingredients such as dietary antioxidants. The aim of this study was to evaluate antioxidant potential of rye and wheat bran using different polarity solvents. Cereal brans were ground to four different particle size fractions and extracted at 10.3 MPa pressure and 80 °C temperature by consecutive application of hexane, acetone and methanol:water (80:20%). The highest extract yield was obtained from rye bran using methanol-water; particle size in most cases had a significant effect. Antioxidant potential of extracts was assessed by ABTS^+•, DPPH^• scavenging, ORAC and total phenols content (TPC) assays. Extraction solvent had a major influence on TPC and antioxidant activity of the extracts. The most active extracts were obtained using methanol:water; rye bran extracts, in general, were stronger antioxidants than wheat bran extracts. For the majority of assays, reduction of particle size resulted in higher antioxidant activity values. However, ABTS^+• scavenging was found to decrease by decreasing particle size of rye bran used for extraction.     

Genome-wide association mapping of starch granule size distribution in common wheat

Starch is a crucial component in wheat endosperm and plays an important role in processing quality. Endosperm of matured wheat grains contains two distinct starch granules (SG), referred to as larger A- and smaller B-granules. In the present study, 166 Chinese bread wheat cultivars planted in four environments were characterized for variation in SG size. A genome-wide association study (GWAS) using the 90 K SNP assay identified 23 loci for percentage volumes of A- and B-granules, and 25 loci for the ratio of A-/B-granules volumes, distributing on 15 chromosomes. Fifteen MTAs were associated with both the percentage volumes of A-, B-granules and the ratio of A-/B-granules volumes. MTAs IWB34623 and IWA3693 on chromosome 7A and IWB22624 and IWA4574 on chromosome 7B associated with the percentage volumes of A- and B-granules consistently identified in multiple environments were considered to be stable. Linear regression analysis showed a significantly negative correlation of the number of favorable alleles with the percentage volumes of A-granules and a significantly positive correlation between the number of favorable alleles and the percentage volumes of B-granules, respectively. The loci identified in this study and associated markers could provide basis for manipulating SG size to obtain superior noodle quality in wheat.     

Characterisation of starch during germination and seedling development of a rice mutant with a high content of resistant starch

To acquire a better understanding of whether RS influences the dynamics of in vivo starch digestion and seed vigour, the high-RS rice mutant RS4 (RS ca. 10%) and the wild type R7954 were used to investigate total amylase activity, seedling vigour, starch content and starch granule structure during germination. RS4 exhibited similar seed vigour to R7954. Amylose and amylopectin in R7954 showed synchronous degradation throughout the whole process, while amylopectin was hydrolysed significantly faster than amylose in RS4 during the earlier germination stages. The starch residues of RS4 after germination (GD) lost endotherm peaks and showed a special X-ray diffraction pattern with only two peaks at around 16.90° and 21.62°, probably due to remnants of amylopectin and its tight crosslinking with the cell wall. The remaining starch after 10 GD, primarily amylopectin may make a critical contribution to total resistant starch content. These results indicated that RS had no negative impact on seed vigour in rice lines, although RS cannot be hydrolysed by α-amylase from human and animal in vitro. By appropriately increasing the special amylopectin fraction, a new breeding programme of high RS crops and improvement in the eating quality of high RS rice varieties might be achieved.     

Hull to caryopsis adhesion and grain skinning in malting barley: Identification of key growth stages in the adhesion process

Strong adhesion between the hull and the caryopsis is essential for barley to be of good malting quality. Poor hull adhesion, a condition known as grain skinning, is undesirable for malting and downstream processes. At present, the processes mediating hull adhesion during grain development are poorly understood. The barley cultivar Chariot was grown in greenhouse conditions and grain development was recorded at defined growth stages to examine the timing of hull adhesion. Initiation of adhesion was first observed when caryopsis fresh weight and volume were approaching their maximum at 19 days after anthesis, during early dough. Hull adhesion was complete by 27 days after anthesis, or soft dough. Sections of developing grains were observed using light and transmission electron microscopy to examine a lipid-rich cementing layer believed to be responsible for adhesion between the hull and the pericarp. Evidence for a lipid-rich cementing material was supported by the observation that neither pectinase nor cellulase effected hull loosening. Grain growth, the presence of globular material originating from the pericarp and an electron dense material in the cementing layer are discussed in relation to hull adhesion. Grain skinning could be caused by poor adherence of cuticular material or inadequate fusion between cuticles.     

Increasing atmospheric CO2 modifies durum wheat grain quality and pasta cooking quality

The present study focused on the quality traits of durum wheat grains (protein and content, gluten content, yellow pigment content), semolina (gluten index and yellow index) and pasta (firmness, yellow index, cooking time) obtained from 12 durum wheat genotypes grown under elevated atmospheric CO₂ concentration in an open field Free Air CO₂ Enrichment (FACE) experiment. The aims were to evaluate the impact of elevated CO₂ on durum wheat pasta making related traits as well as investigate genetic differences existing in a panel of old and modern cultivars. The protein content showed a not significant decrease (7%), the GC decreased significantly (13.3%), while the GI showed an increasing significant tendency (14%). The overall pasta quality (firmness and weight) worsened in ELE. Correlation between all traits and pasta firmness demonstrated that the decrease in pasta firmness under ELE was correlated with GPC and GC while it was not with the GI. All varieties, although to different extent, showed lower pasta firmness values compared to the ambient condition. Among the varieties tested, some were more sensitive than others to the increased atmospheric CO₂ concentration, a finding that can be exploited by breeding for designing novel genotypes with lower sensitivity to increased atmospheric CO₂.     

Oat phenolic content and total antioxidant capacity during grain development

Oats (Avena sativa L.) were revaluated in recent years as a promising crop for improving the nutritional quality of foods, due to their richness in many bioactive compounds, including phenols. These plant secondary metabolites are useful as radical scavenging, and also possess positive biochemical effects against cardiovascular diseases, cancer growth and age-related diseases. Twenty oat cultivars were analyzed for their soluble phenol content (SPC, ranging 0.78–1.09 g_GAE/kg d.m.) and total antioxidant capacity (TAC, ranging 13.99–18.84 mmol TE/kg d.m.). In another experiment, the kinetics of SPC accumulation and TAC in the immature grains of five oat cultivars revealed a marked decrease of both parameters (−48.9% and −72.1%, respectively) from ten days after anthesis to maturity. These results could suggest a possible use of immature oat grains in human nutrition, as it was already proposed for other cereals.