Wheat grain protein accumulation and polymerization mechanisms driven by nitrogen fertilization

Transcriptome and metabolism study reveals impact of nitrogen fertilizer on triticale

Autumn-sown forage triticale can effectively leverage the optimal light and heat conditions in Ningxia, a region that boasts an abundance of light and heat resources sufficient for a single seasonal crop, but limited for two seasons. This not only fully utilizes the limited growing season but also significantly improves grass yield and economic efficiency per unit area. To enhance triticale yield in low-light and low-temperature environments, we investigated the impact of applying different concentrations of nitrogen fertilizer on triticale forage yield. Our findings revealed that nitrogen fertilizer application significantly increased triticale biomass, with the N4 treatment group exhibiting the most profound effect. To further explore the mechanisms behind nitrogen fertilizer's regulation of triticale growth and development, we conducted transcriptomic and metabolomic studies. These studies revealed that nitrogen fertilizer application significantly heightened transcription activity and protein synthesis in triticale, fostering the development of its seeds. Additionally, appropriate concentrations of nitrogen fertilizer significantly promoted photosynthesis. Metabolomic analysis revealed that nitrogen fertilizer application increased the levels of proline and O-phosphoethanolamine, enhancing triticale's stress resistance and supporting its growth and development under adverse conditions.

Cytology, metabolomics, and proteomics reveal the grain filling process and quality difference of wheat

Comparative proteomics and non-target metabolomics, together with physiological and microstructural analyses of wheat grains (at 15, 20, 25, and 30 days after anthesis) from two different quality wheat varieties (Gaoyou 5766 (strong-gluten) and Zhoumai 18) were performed to illustrate the grain filling material dynamics and to search for quality control genes. The differential expressions of 1541 proteins and 406 metabolites were found. They were mostly engaged in protein metabolism, stress/defense, energy metabolism, and amino acid metabolism, and the metabolism of stored proteins and carbohydrates was the major focus of the latter stages. The core proteins and metabolites in the growth process were identified, and the candidate genes for quality differences were screened. In conclusion, this study offers a molecular explanation for the establishment of wheat quality, and it aids in our understanding of the intricate metabolic network between different qualities of wheat at the filling stage.

Planting pattern and nitrogen management strategies: positive effect on yield and quality attributes of Triticum aestivum L. crop

Wheat (Triticum aestivum L.) is a staple food crop that plays a crucial role in global food security. A suitable planting pattern and optimum nitrogen (N) split management are efficient practices for improving wheat production. Therefore, an experiment was performed to explore the effect of N split management and sowing patterns on wheat at the Agronomy Research Farm, The University of Agriculture Peshawar, during rabi season 2020-21 and 2021-22. The treatments consisted of different nitrogen rates of 0, 80, 120, and 160 kg ha- 1 and planting patterns of W, M, broadcast and line sowing. The pooled analysis of both cropping seasons showed that application of 120 kg N ha- 1 increased spikelets spike- 1, grains spike- 1, 1000 grains weight, grain yield, grain N content, evapotranspiration and water use efficiency by 21.9, 16.7, 21.8, 70, 13, 19.9 and 40% as compared to control, respectively. In addition, W and M were observed the best management practices among all planting patterns. The M planting pattern enhanced chlorophyll a, b, carotenoids and evapotranspiration while W plating pattern improved yield components and yield of wheat as compared to broadcast planting patterns. The principal component analysis biplot showed a close association of M and W planting patterns with 120 kg N ha- 1 in most of the studied traits. Hence, it is concluded that split application of 120 kg N ha- 1 in W and M sowing patterns enhanced growth, biochemical traits and water use efficiency, reducing N fertilization from 160 to 120 kg ha- 1 while increasing grain yield of wheat. Hence, it is recommended that application of 120 kg N ha⁻¹ in combination with W and M planting patterns offer a sustainable approach to enhancing wheat production in the alkaline soil conditions of the Peshawar valley.

Comparison of the transcriptome and metabolome of wheat (Triticum aestivum L.) proteins content during grain formation provides insight

Introduction

Wheat is a food crop with a large global cultivation area, and the content and quality of wheat glutenin accumulation are important indicators of the quality of wheat flour.

Methods

To elucidate the gene expression regulation and metabolic characteristics related to the gluten content during wheat grain formation, transcriptomic and metabolomic analyses were performed for the high gluten content of the Xinchun 26 cultivar and the low proteins content of the Xinchun 34 cultivar at three periods (7 d, 14 d and 21 d) after flowering.

Results

Transcriptomic analysis revealed that 5573 unique differentially expressed genes (DEGs) were divided into two categories according to their expression patterns during the three periods. The metabolites detected were mainly divided into 12 classes. Lipid and lipid-like molecule levels and phenylpropanoid and polyketide levels were the highest, and the difference analysis revealed a total of 10 differentially regulated metabolites (DRMs) over the three periods. Joint analysis revealed that the DEGs and DRMs were significantly enriched in starch and sucrose metabolism; the citrate cycle; carbon fixation in photosynthetic organisms; and alanine, aspartate and glutamate metabolism pathways. The genes and contents of the sucrose and gluten synthesis pathways were analysed, and the correlation between gluten content and its related genes was calculated. Based on weighted correlation network analysis (WGCNA), by constructing a coexpression network, a total of 5 specific modules and 8 candidate genes that were strongly correlated with the three developmental stages of wheat grain were identified.

Discussion

This study provides new insights into the role of glutenin content in wheat grain formation and reveals potential regulatory pathways and candidate genes involved in this developmental process.

Wheat GSPs and Processing Quality Are Affected by Irrigation and Nitrogen through Nitrogen Remobilisation

The rheological properties and end-use qualities of many foods are mainly determined by the types and levels of grain storage proteins (GSPs) in wheat. GSP levels are influenced by various factors, including tillage management, irrigation, and fertiliser application. However, the effects of irrigation and nitrogen on GSPs remain unclear. To address this knowledge gap, a stationary split-split block design experiment was carried out in low- and high-fertility (LF and HF) soil, with the main plots subjected to irrigation treatments (W0, no irrigation; W1, irrigation only during the jointing stage; W2, irrigation twice during both jointing and flowering stages), subplots subjected to nitrogen application treatments (N0, no nitrogen application; N180, 180 kg/ha; N240, 240 kg/ha; N300, 300 kg/ha), and cultivars tested in sub-sub plots (FDC5, the strong-gluten cultivar Fengdecun 5; BN207, the medium-gluten cultivar Bainong 207). The results showed that GSP levels and processing qualities were significantly influenced by nitrogen application (p < 0.01), N240 was the optimal nitrogen rate, and the influence of irrigation was dependent on soil fertility. Optimal GSP levels were obtained under W2 treatment at LF conditions, and the content was increased by 17% and 16% for FDC5 and BN207 compared with W0 under N240 treatment, respectively. While the optimal GSP levels were obtained under W1 treatments at HF conditions, and the content was increased by 3% and 21% for FDC5 and BN207 compared with W0 under N240 treatment, respectively. Irrigation and nitrogen application increased the glutenin content by increasing Bx7 and Dy10 levels in FDC5, and by increasing the accumulation of Ax1 and Dx5 in BN207. Gliadins were mainly increased by enhancing α/β-gliadin levels. Correlation analysis indicated that a higher soil nitrate (NO3-N) content increased nitrogen remobilisation in leaves. Path analysis showed that Dy10, Dx5, and γ-gliadin largely determined wet glutenin content (WGC), dough stability time (DST), dough water absorption rate (DWR), and sedimentation value (SV). Therefore, appropriate irrigation and nitrogen application can improve nitrogen remobilisation, GSP levels, and processing qualities, thereby improving wheat quality and production.

Transcriptomic Analysis of the Reduction in Seed Oil Content through Increased Nitrogen Application Rate in Rapeseed (Brassica napus L.)

Nitrogen is essential for improving the seed oil yield of rapeseed (Brassica napus L.). However, the molecular mechanism by which increased nitrogen rates impact seed oil content is largely unknown. Therefore, a field experiment was conducted to determine how three nitrogen application rates (120, 240, and 360 kg ha-1) regulated seed oil content via transcriptomic analysis. The results showed that the seed yield and the protein and total N contents increased from N1 to N3, with average increases of 57.2%, 16.9%, and 79.5%, respectively. However, the seed oil content significantly decreased from N1 to N3, with an average decrease of 8.6%. These results were repeated over a number of years. The quantity of oil protein bodies observed under a transmission electron microscope was in accordance with the ultimate seed oil and protein contents. As the nitrogen application rate increased, a substantial number of genes involved in the photosynthesis, glycolysis, and phenylpropanoid biosynthesis pathways were up-regulated, as were TF families, such as AP2/ERF, MYB, and NAC. The newly identified genes were mainly involved in carbohydrate, lipid, and amino acid metabolism. Metabolic flux analysis showed that most of the genes involved in glycolysis and fatty acid biosynthesis had higher transcript levels in the early development stages. Our results provide new insights into the molecular regulation of rapeseed seed oil content through increased nitrogen application rates.

The Landscapes of Gluten Regulatory Network in Elite Wheat Cultivars Contrasting in Gluten Strength

Yangmai-13 (YM13) is a wheat cultivar with weak gluten fractions. In contrast, Zhenmai-168 (ZM168) is an elite wheat cultivar known for its strong gluten fractions and has been widely used in a number of breeding programs. However, the genetic mechanisms underlying the gluten signatures of ZM168 remain largely unclear. To address this, we combined RNA-seq and PacBio full-length sequencing technology to unveil the potential mechanisms of ZM168 grain quality. A total of 44,709 transcripts were identified in Y13N (YM13 treated with nitrogen) and 51,942 transcripts in Z168N (ZM168 treated with nitrogen), including 28,016 and 28,626 novel isoforms in Y13N and Z168N, respectively. Five hundred and eighty-four differential alternative splicing (AS) events and 491 long noncoding RNAs (lncRNAs) were discovered. Incorporating the sodium-dodecyl-sulfate (SDS) sedimentation volume (SSV) trait, both weighted gene coexpression network analysis (WGCNA) and multiscale embedded gene coexpression network analysis (MEGENA) were employed for network construction and prediction of key drivers. Fifteen new candidates have emerged in association with SSV, including 4 transcription factors (TFs) and 11 transcripts that partake in the post-translational modification pathway. The transcriptome atlas provides new perspectives on wheat grain quality and would be beneficial for developing promising strategies for breeding programs.

Current Progress and Future Prospect of Wheat Genetics Research towards an Enhanced Nitrogen Use Efficiency

To improve the yield and quality of wheat is of great importance for food security worldwide. One of the most effective and significant approaches to achieve this goal is to enhance the nitrogen use efficiency (NUE) in wheat. In this review, a comprehensive understanding of the factors involved in the process of the wheat nitrogen uptake, assimilation and remobilization of nitrogen in wheat were introduced. An appropriate definition of NUE is vital prior to its precise evaluation for the following gene identification and breeding process. Apart from grain yield (GY) and grain protein content (GPC), the commonly recognized major indicators of NUE, grain protein deviation (GPD) could also be considered as a potential trait for NUE evaluation. As a complex quantitative trait, NUE is affected by transporter proteins, kinases, transcription factors (TFs) and micro RNAs (miRNAs), which participate in the nitrogen uptake process, as well as key enzymes, circadian regulators, cross-talks between carbon metabolism, which are associated with nitrogen assimilation and remobilization. A series of quantitative genetic loci (QTLs) and linking markers were compiled in the hope to help discover more efficient and useful genetic resources for breeding program. For future NUE improvement, an exploration for other criteria during selection process that incorporates morphological, physiological and biochemical traits is needed. Applying new technologies from phenomics will allow high-throughput NUE phenotyping and accelerate the breeding process. A combination of multi-omics techniques and the previously verified QTLs and molecular markers will facilitate the NUE QTL-mapping and novel gene identification.

Effect of Production Technology Intensity on the Grain Yield, Protein Content and Amino Acid Profile in Common and Durum Wheat Grain

Products derived from wheat grains are an important source of protein in the daily diet of people in many parts of the world. The biological value of protein is determined by its amino acid composition and the proportions of the individual amino acids. Synthesis of these compounds in wheat grains is influenced by genetic factors, as well as habitat conditions and the agrotechnology applied in cultivation. The aim of this study was to assess the effect of production technology (integrated, intensive) on the grain yield and the content amino acid profile of protein in common and durum wheat grain. Field research was conducted at the Experimental Station IUNG-PIB in Osiny (Poland) in two growing seasons. It was found that grain yield significantly depended on the weather conditions in the years of harvesting and genotype, but did not depend on the production technology. On the other hand, the protein content and their amino acid composition depended significantly on the production technology and genotype. A significantly higher content of protein substances was found in durum wheat grain. Increasing the intensity of production technology had a positive effect on the total protein content and the content of individual amino acids, both exogenous and endogenous. The amino acid limiting the biological value of protein contained in grains of both wheat species was lysine, and the deficiency of this amino acid was significantly lower in grain protein from intensive than integrated cultivation technology.

A community resource to mass explore the wheat grain proteome and its application to the late-maturity alpha-amylase (LMA) problem

BACKGROUND

Late-maturity alpha-amylase (LMA) is a wheat genetic defect causing the synthesis of high isoelectric point alpha-amylase following a temperature shock during mid-grain development or prolonged cold throughout grain development, both leading to starch degradation. While the physiology is well understood, the biochemical mechanisms involved in grain LMA response remain unclear. We have applied high-throughput proteomics to 4,061 wheat flours displaying a range of LMA activities. Using an array of statistical analyses to select LMA-responsive biomarkers, we have mined them using a suite of tools applicable to wheat proteins.

RESULTS

We observed that LMA-affected grains activated their primary metabolisms such as glycolysis and gluconeogenesis; TCA cycle, along with DNA- and RNA- binding mechanisms; and protein translation. This logically transitioned to protein folding activities driven by chaperones and protein disulfide isomerase, as well as protein assembly via dimerisation and complexing. The secondary metabolism was also mobilized with the upregulation of phytohormones and chemical and defence responses. LMA further invoked cellular structures, including ribosomes, microtubules, and chromatin. Finally, and unsurprisingly, LMA expression greatly impacted grain storage proteins, as well as starch and other carbohydrates, with the upregulation of alpha-gliadins and starch metabolism, whereas LMW glutenin, stachyose, sucrose, UDP-galactose, and UDP-glucose were downregulated.

CONCLUSIONS

To our knowledge, this is not only the first proteomics study tackling the wheat LMA issue but also the largest plant-based proteomics study published to date. Logistics, technicalities, requirements, and bottlenecks of such an ambitious large-scale high-throughput proteomics experiment along with the challenges associated with big data analyses are discussed.

Does Nitrogen Fertilization Affect the Secondary Structures of Gliadin Proteins in Hypoallergenic Wheat?

One of the macronutrients indispensable for plant growth and development is nitrogen (N). It is responsible for starch and storage protein (gliadins and glutenins) biosynthesis and, in consequence, influences kernels’ quality and yields. However, applying N-fertilizers increases gluten content in wheat, and it may intensify the risk of developing allergy symptoms in gluten-sensitive individuals. The purpose of our research was to analyse whether and how the elimination of N-fertilizers during the cultivation of wasko.gl− wheat (modified genotype lacking ω-gliadins) changes the secondary structures of gliadin proteins. To this aim, using the FT-Raman technique, we examined flour and gliadin protein extracts obtained from kernels of two winter wheat lines: wasko.gl+ (with a full set of gliadin proteins) and wasko.gl− (without ω-gliadin fraction) cultivated on two different N-fertilization levels—0 and 120 kg N·ha⁻¹. On the basis of the obtained results, we proved that nitrogen fertilization does not have a major impact on the stability of the secondary structures of gliadin proteins for wasko.gl− wheat line with reduced allergenic properties. Furthermore, the results presented herein suggest the possibility of increasing the stability of glutenin structures as a result of the N-fertilization of wasko.gl− wheat line, which gives hope for its use in the production of wheat articles devoted to people suffering from diseases related to gluten sensitivity.

Optimized seeding rate and nitrogen topdressing ratio for simultaneous improvement of grain yield and bread-making quality in bread wheat sown on different dates

BACKGROUND

Sowing date, seeding rate, and nitrogen (N) topdressing ratio have strong effects on grain yield (GY) and bread-making quality (BQ) in bread wheat. Simultaneous improvement in GY and BQ in bread wheat has long been a challenge due to the inverse relationship between GY and grain protein concentration (GPC). In this study, we investigated whether the GY and BQ of bread wheat sown on different dates could be improved simultaneously by optimizing the seeding rate and the N topdressing ratio.

RESULTS

Delaying sowing beyond a certain period led to decreases in both GY and BQ. Optimizing the seeding rate and N topdressing ratio enhanced the N uptake during pre- and post-anthesis, as well as N remobilization during grain filling for all wheat plants sown on different dates, thereby increasing the GPC and the total N per grain (N_tot ). Consequently, grain protein composition was improved, resulting in an increased glutenin/gliadin ratio, sodium dodecyl sulfate-insoluble glutenin/total glutenin (i.e., glutenin polymerization index), and high-molecular-weight glutenin subunit/ low-molecular-weight glutenin subunit (HMW-GS/LMW-GS) ratio. Increased GPC and improved grain protein composition enhanced BQ.

CONCLUSION

The mechanism underlying simultaneous improvement in GY and GPC as well as N_tot was the greater increase in N accumulation in grains per unit area relative to increases in GY, or total grain number per unit area. The GY and BQ can be improved simultaneously regardless of sowing date by optimizing the seeding rate and N topdressing ratio via enhanced N uptake and N remobilization into grains. © 2021 Society of Chemical Industry.

Wheat Quality Formation and Its Regulatory Mechanism

Elucidation of the composition, functional characteristics, and formation mechanism of wheat quality is critical for the sustainable development of wheat industry. It is well documented that wheat processing quality is largely determined by its seed storage proteins including glutenins and gliadins, which confer wheat dough with unique rheological properties, making it possible to produce a series of foods for human consumption. The proportion of different gluten components has become an important target for wheat quality improvement. In many cases, the processing quality of wheat is closely associated with the nutritional value and healthy effect of the end-products. The components of wheat seed storage proteins can greatly influence wheat quality and some can even cause intestinal inflammatory diseases or allergy in humans. Genetic and environmental factors have great impacts on seed storage protein synthesis and accumulation, and fertilization and irrigation strategies also greatly affect the seed storage protein content and composition, which together determine the final end-use quality of wheat. This review summarizes the recent progress in research on the composition, function, biosynthesis, and regulatory mechanism of wheat storage proteins and their impacts on wheat end-product quality.

Proteomics characterization nitrogen fertilizer promotes the starch synthesis and metabolism and amino acid biosynthesis in common buckwheat

Nitrogen (N) affects common buckwheat quality by affecting starch and amino acids (AAs) content, but its molecular mechanism is still unclear. We selected two common buckwheat varieties with high and low starch content, and designed two treatments with 180 and 0 kg N/ha. Application of high-N led to significant increases in starch, amylose and amylopectin content. Of 1337 differentially expressed proteins (DEPs) induced by high-N conditions. 472DEPs were significantly upregulated and 176DEPs downregulated for Xinong9976. 239DEPs were significantly upregulated and 126DEPs downregulated for Beizaosheng. The six alpha-glucan phosphorylases, three alpha-amylases, one granule-bound starch synthase 1 and one sucrose synthase exhibited higher expression at the 180 kg N/ha than at the 0 kg N/ha. In addition, high-N application promoted arginine, leucine, isoleucine and valine biosynthesis. This study revealed the effect of N on the starch and AA content of common buckwheat and its mechanism. The crucial proteins identified may develop the quality of common buckwheat.

Grains - a major source of sustainable protein for health

Cereal grains are the main dietary source of energy, carbohydrates, and plant proteins world-wide. Currently, only 41% of grains are used for human consumption, and up to 35% are used for animal feed. Cereals have been overlooked as a source of environmentally sustainable and healthy plant proteins and could play a major role in transitioning towards a more sustainable food system for healthy diets. Cereal plant proteins are of good nutritional quality, but lysine is often the limiting amino acid. When consumed as whole grains, cereals provide health-protecting components such as dietary fiber and phytochemicals. Shifting grain use from feed to traditional foods and conceptually new foods and ingredients could improve protein security and alleviate climate change. Rapid development of new grain-based food ingredients and use of grains in new food contexts, such as dairy replacements and meat analogues, could accelerate the transition. This review discusses recent developments and outlines future perspectives for cereal grain use.

Impact and mechanism of sulphur-deficiency on modern wheat farming nitrogen-related sustainability and gliadin content

Two challenges that the global wheat industry is facing are a lowering nitrogen-use efficiency (NUE) and an increase in the reporting of wheat-protein related health issues. Sulphur deficiencies in soil has also been reported as a global issue. The current study used large-scale field and glasshouse experiments to investigate the sulphur fertilization impacts on sulphur deficient soil. Here we show that sulphur addition increased NUE by more than 20% through regulating glutamine synthetase. Alleviating the soil sulphur deficiency highly significantly reduced the amount of gliadin proteins indicating that soil sulphur levels may be related to the biosynthesis of proteins involved in wheat-induced human pathologies. The sulphur-dependent wheat gluten biosynthesis network was studied using transcriptome analysis and amino acid metabolomic pathway studies. The study concluded that sulphur deficiency in modern farming systems is not only having a profound negative impact on productivity but is also impacting on population health.

The α-Gliadins in Bread Wheat: Effect of Nitrogen Treatment on the Expression of the Major Celiac Disease Immunogenic Complex in Two RNAi Low-Gliadin Lines

Celiac Disease (CD) is an autoimmune disorder that affects approximately 1% of the worldwide population. The α-gliadins of wheat contain the 33-mer peptide, the most active peptide in CD both in adults and pediatric patients. In this study, we have characterized the variants and expression profile of an α-gliadins amplicon, harboring the 33-mer peptide, in two low-gliadin RNAi wheat lines, under two different Nitrogen (N) treatments. We estimated that the amplicon expands 45 different α-gliadin variants with high variability due to length, randomly distributed SNPs, and the presence of encoded CD epitopes. Expression of this amplicon is reduced in both RNAi lines in comparison to the wild type. High N treatment significantly increases transcripts of the amplicon in the wild type, but not in the transgenic lines. Classification of α-gliadin variants, considering the number of epitopes, revealed that amplicon variants containing the full complement of 33-mer peptide were affected by N treatment, increasing their expression when N was increased. Line D793 provided higher and more stable silencing through different N fertilization regimes, expressing fewer CD epitopes than D783. Results of this study are important for better understanding of RNAi α-gliadin silencing in response to N treatments, and for undertaking new strategies by RNAi or CRISPR/Cas toward obtaining new varieties suitable for people suffering gluten intolerances.

Comparative analysis of developing grain transcriptome reveals candidate genes and pathways improving GPC in wheat lines derived from wild emmer

The grain protein content (GPC) in modern wheat is inherently low. Wild emmer wheat (Triticum turgidum ssp. dicoccoides, 2n = 4x = 28, AABB) gene pool harbors wide genotypic variations in GPC. However, the characterization of candidate genes associated with high GPC is a challenge due to the complex characteristic of this trait. In the current study, we performed RNA-seq analysis on developing grains of wild emmer genotype D1, common wheat CN16, and their hexaploid wide hybrid BAd107-4 with contrasting GPC. We have found a total of 39,795 expressed genes on chromosomes A and B, of which 24,152 were shared between D1, CN16, and BAd107-4. From 1744 differentially expressed genes (DEGs), 1203 were downregulated and 541 were upregulated in the high GPC (D1+BAd107-4) compared with low GPC (CN16) groups. The majority of DEGs were associated with protein processing in endoplasmic reticulum, starch and sucrose metabolism, galactose metabolism, and protein export pathways. Expression levels of nine randomly selected genes were verified by qRT-PCR, which was consistent with the transcriptome data. The present database will help us to understand the potential regulation networks underlying wheat grain protein accumulation and provide the foundation for simultaneous improvement of grain protein content and yield in wheat breeding programs.

Coordination of carbon and nitrogen accumulation and translocation of winter wheat plant to improve grain yield and processing quality

The objective of this work was to characterize the accumulation of carbon (C) and nitrogen (N), and the translocation of wheat (Triticum aestivum L.) cultivars to achieve both high-quality and high-yield. Twenty-four wheat cultivars, including 12 cultivars containing high-quality gluten subunit 5 + 10 at Glu-D1, and 12 cultivars with no Glu-D1 5 + 10, were planted at Yuanyang and Xuchang in Henan Province, during 2016-2017, and 2017-2018 cropping seasons. Wheat cultivars containing Glu-D1 5 + 10 had an advantage in grain quality traits. Significant difference (P < 0.05) was observed for grain protein concentration (GPC) between 5 + 10 group and no 5 + 10 group. Grain yield (GY) was significantly correlated with kernel number (KN) (r = 0.778, P < 0.01), thousand-kernel weight (TKW) (r = 0.559, P < 0.01), dry matter accumulation at post-anthesis (r = 0.443, P < 0.05), and stem water-soluble carbohydrate (WSC) accumulation (r = 0.487, P < 0.05) and translocation amount (r = 0.490, P < 0.05). GPC, dough stability time (DST) and nitrogen agronomic efficiency (NAE) were significantly correlated with nitrogen accumulation (NAA) at maturity stage (r = 0.524, = 0.404, = 0.418, P < 0.01, < 0.05, < 0.05, respectively), and nitrogen translocation amount (r = 0.512, = 0.471, = 0.405, P < 0.05, < 0.05, < 0.05, respectively). These results suggest that good-quality, high-yield, and high-efficiency could achieve through the selection of high-quality wheat cultivars and coordination of C and N accumulation and translocation. High-quality gluten subunit gene Glu-D1 5 + 10 and stem WSC could be used as a selection index for breeding and production of high-quality and high-yield wheat.

HMW-GS at Glu-B1 Locus Affects Gluten Quality Possibly Regulated by the Expression of Nitrogen Metabolism Enzymes and Glutenin-Related Genes in Wheat

In this study, we investigated the effect of high-molecular-weight glutenin subunits (HMW-GSs) on gluten quality and glutenin synthesis based on the cytological, physicochemical, and transcriptional levels using Xinong1718 and its three near-isogenic lines (NILs). Cytological observations showed that the endosperm of Glu-1Bh with Bx14+By15 accumulated more abundant and larger protein bodies at 10 and 16 days after anthesis than the other NILs. Glu-1Bh exhibited higher nitrogen metabolism enzyme gene expression and activity levels. The transcriptional levels of genes encoding HMW-GSs, protein folding, and transcription factors differed significantly among the NILs, and they were highest in Glu-1Bh. Our results demonstrate that variations in the expression patterns of nitrogen metabolism and glutenin synthesis-related genes may account for the differences in the accumulation of glutenin, glutenin macropolymers, and protein bodies, thereby affecting the structural and thermal stability of gluten. These findings provide novel insights into how different HMW-GSs might improve the quality of wheat.

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.

Effects of Nitrogen Application in the Wheat Booting Stage on Glutenin Polymerization and Structural-Thermal Properties of Gluten with Variations in HMW-GS at the Glu-D1 Locus

Wheat gluten properties can be improved by the application of nitrogen. This study investigates the effects of nitrogen application in the booting stage on glutenin polymerization during grain-filling and structural-thermal properties of gluten based on the high-molecular-weight glutenin subunits (HMW-GSs) using near-isogenic lines (Glu-1Da and Glu-1Dd). The nitrogen rate experiment included rates of 0, 60, 90, and 120 kg N ha^-1 applied with three replicates. Nitrogen significantly improved the grain quality traits (wet gluten contents, Zeleny sedimentation values, and maximum resistance) and dough strength (dough development time, dough stability time, and protein weakening), especially in wheat with the Glu-1Da allele. Nitrogen increased the protein composition contents, proportions of glutenins and HMW-GSs, and disulfide bond concentration in the flours of Glu-1Da and Glu-1Dd, and accelerated the polymerization of glutenins (appearing as glutenin macropolymer) during grain-filling, where nitrogen enhanced the accumulation and polymerization of glutenins more for line containing Glu-1Da than Glu-1Dd. The β-sheets, α-helix/β-sheet ratio, microstructures, and thermal stability were also improved to a greater degree by nitrogen for gluten with Glu-1Da compared to Glu-1Dd. Nitrogen treatment was highly effective at improving the gluten structural‒thermal properties of wheat in the booting stage, especially with inferior glutenin subunits.

Absence of Dx2 at Glu-D1 Locus Weakens Gluten Quality Potentially Regulated by Expression of Nitrogen Metabolism Enzymes and Glutenin-Related Genes in Wheat

Absence of high-molecular-weight glutenin subunit (HMW-GS) Dx2 weakens the gluten quality, but it is unclear how the absence of Dx2 has these effects. Thus, we investigated the gluten quality in terms of cytological, physicochemical, and transcriptional characteristics using two near-isogenic lines with Dx2 absent or present at Glu-D1 locus. Cytological observations showed that absence of Dx2 delayed and decreased the accumulation of protein bodies (PBs), where fewer and smaller PBs formed in the endosperm. The activity and gene expression levels of nitrogen assimilation and proteolysis enzymes were lower in HMW-D1a without Dx2 than HMW-D1p with Dx2, and thus less amino acid was transported for protein synthesis in the grains. The expression pattern of genes encoding Glu-1Dx2+1Dy12 was similar to those of three transcription factors, where these genes were significantly down-regulated in HMW-D1a than HMW-D1p. Three genes involving with glutenin polymerization were also down-regulated in HMW-D1a. These results may explain the changes in the glutenin and glutenin macropolymer (GMP) levels during grain development. Therefore, we suggest that the lower nitrogen metabolism capacity and expression levels of glutenin synthesis-related genes in HMW-D1a accounted for the lower accumulation of glutenin, GMP, and PBs, thereby weakening the structural‒thermal properties of gluten.

Introgression of an expressed HMW 1Ay glutenin subunit allele into bread wheat cv. Lincoln increases grain protein content and breadmaking quality without yield penalty

An expressed HMW glutenin subunit Glu-Ay showed positive impacts on a range of wheat processing quality and yield traits. The grain protein compositions are significantly optimised for baking, resulting in a better breadmaking quality. The unique breadmaking properties of wheat flour are related to the quality and quantity of high-molecular weight glutenin subunits (HMW-GSs) present in the grain. In the current study, the silent 1Ay HMW-GS allele, present in most bread wheat cultivars, was replaced by the expressed 1Ay21* allele, which was introgressed into Australian bread wheat cultivar Lincoln by a backcrossing and selfing scheme. Stability of gene expression and the effect of the introgressed 1Ay21* subunit on protein composition, agronomic traits, flour functionality, and breadmaking quality were studied using BC4F5 grain grown in glasshouse and field. Field phenotyping and grain quality testing showed that the 1Ay21* gene conferred significant improvements to a range of traits, including an increase in grain protein content by up to 9%, UPP% by up to 24%, bread volume by up to 28%. The glasshouse experiment and one of the field trials showed positive 1Ay21* effects on yield, while one field trial showed one significant effects. This indicates that expression of the 1Ay21* gene has the potential of simultaneously increasing protein content and grain yield under certain environment. The qualitative improvements of the grain also led to a reduction of the energy required during the baking process in addition to the significant positive effects on bread quality.

Water Regime and Nitrogen Management to Cope with Wheat Yield Variability under the Mediterranean Conditions of Southern Portugal

Global climate change accentuates the seasonal and interannual irregularity of temperature and precipitation of the Mediterranean climate. The consequences of this variability on wheat production are felt on its development cycle and productivity, making the production chain of this crop vulnerable to the occurrence of years with abnormal distributions of precipitation and with extreme temperatures. Adaptation strategies like irrigation or fertilization can help to cope with the negative impacts of climate uncertainty. This study evaluated the effects of water regime and nitrogen (N) fertilization techniques on wheat production in southern Portugal based on the results of three trials conducted in two agricultural years (2016/2017 and 2017/2018) with contrasting climate conditions. Phenology and yield were evaluated by comparing water regimes (R1, full irrigation; R2, supplemental irrigation at four stages: start of stem extension, booting, anthesis, grain filling; R0, rainfed (in 2017/2018)) and N fertilization splitting/timing and type (conventional and enhanced efficiency fertilizers (EEFs): controlled-release N, stabilized with nitrification inhibitor, and stabilized with urease inhibitor). Significant effects of water regime on grain yield were obtained in 2016/2017, a year with extreme aridity and high water requirements felt from the tillering stage, in the trial with conventional fertilizers. In 2017/2018, when a beneficial seasonal rainfall distribution occurred, water regime did not influence grain yield, pointing to the feasibility of supplementary irrigation to maximize water productivity. Nitrogen fertilization influenced yield and its components, with the highest values of grain yield being obtained with conventional fertilizer. Regardless of the possible effects on grain quality, the use of EEF did not prove to have an indisputable effect on wheat yield in the conditions under which the trials were conducted. Comparison of the results in the two years accentuates the need to continue the evaluation of the influence of agronomic management in wheat production in the context of adaptation to the climatic uncertainty in Mediterranean regions.

Transcriptomic and Metabolomics Analysis of Different Endosperm Region under Nitrogen Treatments

Storage protein distribution in wheat-grain endosperm is heterogeneous, but the underlying molecular mechanism remains unclear. Two parts of the endosperm region, the innermost endosperm (IE) region and the remaining endosperm (RE) region, grown under low nitrogen (LN) and high nitrogen (HN) treatments were used to perform metabolomic and transcriptomic analysis. We identified 533 and 503 differentially expressed genes (DEGs) with at least a two-fold expression change (p < 0.05) between IE and RE, among which 81 and 78 transcripts under LN and HN, respectively, related to carbon and nitrogen metabolism, and encoded transcription factors or proteins involved in post-translational modification (PTM). The significantly differentially abundant metabolites between IE and RE were mainly amino acids, N-compounds, carbohydrates, and nucleic acids. More upregulated transcripts and metabolites were identified in RE than IE under HN conditions, indicating that HN activates metabolism in the endosperm periphery. In addition to carbon and nitrogen metabolism, transcription factors and protein PTMs, such as phosphorylation and acetylation, might determine the protein heterogeneous distribution between IE and RE and its response to nitrogen fertilizer supply.