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.     

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.     

Effect of allelic variation at the Glu-3/Gli-1 loci on breadmaking quality parameters in hexaploid wheat (Triticum aestivum L.)

Low molecular weight glutenin subunits (LMW-GS) encoded by the Glu-3 loci are known to contribute to wheat breadmaking quality. However, the specific effect of individual Glu-3 alleles is not well understood due to their complex protein banding patterns in SDS-PAGE and tight linkage with gliadins at the Gli-1 locus. Using DNA markers and a backcross program, we developed a set of nine near isogenic lines (NILs) including different Glu-A3/Gli-A1 or Glu-B3/Gli-B1 alleles in the genetic background of the Argentine variety ProINTA Imperial. The nine NILs and the control were evaluated in three different field trials in Argentina. Significant genotype-by-environment interactions were detected for most quality parameters indicating that the effects of the Glu-3/Gli-1 alleles are modulated by environmental differences. None of the NILs showed differences in total flour protein content, but relative changes in the abundance of particular classes of proteins cannot be ruled out. On average, the Glu-A3f, Glu-B3b, Glu-B3g and Glu-B3i_Man alleles were associated with the highest values in gluten strength-related parameters, while Glu-A3e, Glu-B3a and Glu-B3i_Chu were consistently associated with weak gluten and low quality values. The value of different Glu-3/Gli-1 allele combinations to improve breadmaking quality is discussed.     

TaSnRK2.4 is a vital regulator in control of thousand-kernel weight and response to abiotic stress in wheat

Sucrose non-fermenting 1-related protein kinase 2(Sn RK2) is a plant-specific serine/threonine kinase involved in response to adverse environmental stimuli. Previous studies showed that Ta Sn RK2.4 was involved in response to abiotic stresses and conferred enhanced tolerance to multiple stresses in Arabidopsis. Further experiments were performed to decipher the underlying mechanisms and discover new functions. The genomic sequences of Ta Sn RK2.4 s locating on chromosome 3 A, 3 B and 3 D were obtained. Sequencing identified one and 13 variations of Ta Sn RK2.4-3 A and Ta Sn RK2.4-3 B, respectively, but no variation was detected in Ta Sn RK2.4-3 D. The markers 2.4 AM1, 2.4 BM1 and 2.4 BM2 were developed based on three variations. Association analysis showed that both Ta Sn RK2.4-3 A and Ta Sn RK2.4-3 B were significantly associated with thousand-kernel weight(TKW), and that SNP3 A-T and SNP3 B-C were favorable alleles for higher TKW. Yeast two-hybrid and split luciferase assays showed that Ta Sn RK2.4 physically interacted with abiotic stress responsive protein Ta LTP3, suggesting that Ta Sn RK2.4 enhanced abiotic stress tolerance by activating Ta LTP3. Our studies suggested that Ta Sn RK2.4 have potential in improving TKW and response to abiotic stress.     

Alkylresorcinol composition allows the differentiation of Triticum spp. having different degrees of ploidy

Total alkylresorcinol (AR) content and homologue composition were assessed in whole grain flours of 15 varieties each of bread wheat, durum, spelt, emmer, and einkorn grown in four different environments. Bread wheat (761 ± 92 μg/g DM) and spelt (743 ± 57 μg/g) belonging to the hexaploid species showed higher AR concentrations than the tetraploid durum (654 ± 48 μg/g, p < 0.05), while the concentrations found in the diploid einkorn (737 ± 91 μg/g) and the tetraploid emmer (697 ± 94 μg/g) did not significantly differ from the other species. The AR content showed a remarkable heritability and, thus, seemed to be mainly determined by genetic factors. If ARs were assumed to be deposited within a specific AR-rich layer of the kernel, AR levels of all varieties would easily surpass their minimal inhibitory concentrations against fungal pathogens within this barrier layer. Although the AR carrying a C21:0 side chain was the main homologue in all species, the levels of all AR homologues and their relative composition significantly differed between hexaploid (bread wheat and spelt), tetraploid (durum and emmer) and diploid (einkorn) species. Consequently, a clear-cut differentiation of Triticum species and derived whole grain flours according to their degrees of ploidy was established based on concentrations of saturated C₁₇-, C₁₉-, C₂₁-, C₂₃-, and C₂₅-substituted ARs.     

The agronomic performance and nutritional content of oat and barley varieties grown in a northern maritime environment depends on variety and growing conditions

Warmer temperatures and increasing interest in high provenance food and drink products are creating new opportunities for cereal growing in northern Europe. Nevertheless, cultivation of oats and barley in these areas for malting and milling remains a challenge, primarily because of the weather, and there are few reports of their nutritional content from this region. In this study, trials in Orkney compared agronomic characteristics and nutritional content of recommended UK oat and barley varieties with Scandinavian varieties over three years. For a subset of varieties, nutritional content was compared with samples cultivated in more southerly sites. For Orkney, barley was considered a more suitable crop than oats because varieties matured earlier. In both crops, Scandinavian varieties matured earlier than UK varieties and some produced comparable yields. The range of values for macronutrients and minerals in oats and barley in Orkney were similar to those reported previously for other locations, but there were some significant differences attributable to variety and year. Compared with grain samples from more southerly locations, oats in Orkney had a significantly lower β-glucan and higher sodium content. The lower β-glucan may have resulted from higher rainfall and lower temperatures during the months of grain filling and maturation.     

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.