Differential representation of albumins and globulins during grain development in durum wheat and its possible functional consequences

Genome-Wide Expression Analysis of Glyoxalase I Genes Under Hyperosmotic Stress and Existence of a Stress-Responsive Mitochondrial Glyoxalase I Activity in Durum Wheat (Triticum durum Desf.)

Glyoxalase I (GLYI) catalyzes the rate-limiting step of the glyoxalase pathway that, in the presence of GSH, detoxifies the cytotoxic molecule methylglyoxal (MG) into the non-toxic D-lactate. In plants, MG levels rise under various abiotic stresses, so GLYI may play a crucial role in providing stress tolerance. In this study, a comprehensive genome database analysis was performed in durum wheat (Triticum durum Desf.), identifying 27 candidate GLYI genes (TdGLYI). However, further analyses of phylogenetic relationships and conserved GLYI binding sites indicated that only nine genes encode for putative functionally active TdGLYI enzymes, whose distribution was predicted in three different subcellular compartments, namely cytoplasm, plastids and mitochondria. Expression profile by qRT-PCR analysis revealed that most of the putative active TdGLYI genes were up-regulated by salt and osmotic stress in roots and shoots from 4-day-old seedlings, although a different behavior was observed between the two types of stress and tissue. Accordingly, in the same tissues, hyperosmotic stress induced an increase (up to about 40%) of both GLYI activity and MG content as well as a decrease of GSH (up to about -60%) and an increase of GSSG content (up to about 7-fold) with a consequent strong decrease of the GSH/GSSG ratio (up to about -95%). Interestingly, in this study, we reported the first demonstration of the existence of GLYI activity in highly purified mitochondrial fraction. In particular, GLYI activity was measured in mitochondria from durum wheat (DWM), showing hyperbolic kinetics with Km and Vmax values equal to 92 ± 0.2 μM and 0.519 ± 0.004 μmol min^-1 mg^-1 of proteins, respectively. DWM-GLYI resulted inhibited in a competitive manner by GSH (Ki = 6.5 ± 0.7 mM), activated by Zn²⁺ and increased, up to about 35 and 55%, under salt and osmotic stress, respectively. In the whole, this study provides basis about the physiological significance of GLYI in durum wheat, by highlighting the role of this enzyme in the early response of seedlings to hyperosmotic stress. Finally, our results strongly suggest the existence of a complete mitochondrial GLYI pathway in durum wheat actively involved in MG detoxification under hyperosmotic stress.

Genome-Wide Expression Analysis of Glyoxalase I Genes Under Hyperosmotic Stress and Existence of a Stress-Responsive Mitochondrial Glyoxalase I Activity in Durum Wheat (Triticum durum Desf.)

Glyoxalase I (GLYI) catalyzes the rate-limiting step of the glyoxalase pathway that, in the presence of GSH, detoxifies the cytotoxic molecule methylglyoxal (MG) into the non-toxic D-lactate. In plants, MG levels rise under various abiotic stresses, so GLYI may play a crucial role in providing stress tolerance. In this study, a comprehensive genome database analysis was performed in durum wheat (Triticum durum Desf.), identifying 27 candidate GLYI genes (TdGLYI). However, further analyses of phylogenetic relationships and conserved GLYI binding sites indicated that only nine genes encode for putative functionally active TdGLYI enzymes, whose distribution was predicted in three different subcellular compartments, namely cytoplasm, plastids and mitochondria. Expression profile by qRT-PCR analysis revealed that most of the putative active TdGLYI genes were up-regulated by salt and osmotic stress in roots and shoots from 4-day-old seedlings, although a different behavior was observed between the two types of stress and tissue. Accordingly, in the same tissues, hyperosmotic stress induced an increase (up to about 40%) of both GLYI activity and MG content as well as a decrease of GSH (up to about -60%) and an increase of GSSG content (up to about 7-fold) with a consequent strong decrease of the GSH/GSSG ratio (up to about -95%). Interestingly, in this study, we reported the first demonstration of the existence of GLYI activity in highly purified mitochondrial fraction. In particular, GLYI activity was measured in mitochondria from durum wheat (DWM), showing hyperbolic kinetics with Km and Vmax values equal to 92 ± 0.2 μM and 0.519 ± 0.004 μmol min^-1 mg^-1 of proteins, respectively. DWM-GLYI resulted inhibited in a competitive manner by GSH (Ki = 6.5 ± 0.7 mM), activated by Zn²⁺ and increased, up to about 35 and 55%, under salt and osmotic stress, respectively. In the whole, this study provides basis about the physiological significance of GLYI in durum wheat, by highlighting the role of this enzyme in the early response of seedlings to hyperosmotic stress. Finally, our results strongly suggest the existence of a complete mitochondrial GLYI pathway in durum wheat actively involved in MG detoxification under hyperosmotic stress.

Effects of Elevated CO2 and Heat on Wheat Grain Quality

Wheat is one of the most important staple foods in temperate regions and is in increasing demand in urbanizing and industrializing countries such as China. Enhancing yield potential to meet the population explosion around the world and maintaining grain quality in wheat plants under climate change are crucial for food security and human nutrition. Global warming resulting from greenhouse effect has led to more frequent occurrence of extreme climatic events. Elevated atmospheric CO2 concentration (eCO2) along with rising temperature has a huge impact on ecosystems, agriculture and human health. There are numerous studies investigating the eCO2 and heatwaves effects on wheat growth and productivity, and the mechanisms behind. This review outlines the state-of-the-art knowledge regarding the effects of eCO2 and heat stress, individually and combined, on grain yield and grain quality in wheat crop. Strategies to enhance the resilience of wheat to future warmer and CO2-enriched environment are discussed.

Biostimulant impacts of Glutacetine® and derived formulations (VNT1 and VNT4) on the bread wheat grain proteome

Nitrogen (N) fertilizer is essential to ensure grain yield and quality in bread wheat. Improving N use efficiency is therefore crucial for wheat grain protein quality. In the present work, we analysed the effects on the winter wheat grain proteome of biostimulants containing Glutacetine® or two derived formulations (VNT1 and 4) when mixed with urea-ammonium-nitrate fertilizer. A large-scale quantitative proteomics analysis of two wheat flour fractions produced a dataset of 4369 identified proteins. Quantitative analysis revealed 9, 39 and 96 proteins with a significant change in abundance after Glutacetine®, VNT1 and VNT4 treatments, respectively, with a common set of 11 proteins that were affected by two different biostimulants. The major effects impacted proteins involved in (i) protein synthesis regulation (mainly ribosomal and binding proteins), (ii) defence and responses to stresses (including chitin-binding protein, heat shock 70 kDa protein 1 and glutathione S-transferase proteins), (iii) storage functions related to gluten protein alpha-gliadins and starch synthase and (iv) seed development with proteins implicated in protease activity, energy machinery, and the C and N metabolism pathways. Altogether, our study showed that Glutacetine®, VNT1 and VNT4 biostimulants positively affected protein composition related to grain quality. Data are available via ProteomeXchange with identifier PXD021513. SIGNIFICANCE: We performed a large-scale quantitative proteomics study of the total protein extracts from flour samples to determine the effect of Glutacetine®-based biostimulants treatment on the protein composition of bread wheat grain. To our knowledge, only a few studies in the literature have applied proteomic approaches to study bread wheat grains and in particular to investigate the effect of biostimulants on the grain proteome of this cereal crop. In addition, most approaches used fractional extraction of proteins to target reserve proteins followed electrophoresis which leads to low identification rate of proteins. We identified and quantified a large protein dataset of 4369 proteins and determined ontological class of proteins affected by biostimulants treatments. Our proteomics investigation revealed the important role of these new biostimulants in achieving significant changes in protein synthesis regulation, storage functions, protease activity, energy machinery, C and N metabolism pathways and responses to biotic and abiotic stresses in grain.

Comparative Analysis of in vitro Digestibility and Immunogenicity of Gliadin Proteins From Durum and Einkorn Wheat

Recent studies suggested that gliadin proteins from the ancient diploid einkorn wheat Triticum monococcum retained a reduced number of immunogenic peptides for celiac disease patients because of a high in vitro digestibility with respect to hexaploid common wheat. In this study, we compared the immunological properties of gliadins from two Triticum monococcum cultivars (Hammurabi and Norberto-ID331) with those of a Triticum durum cultivar (Adamello). Gliadins were digested by mimicking the in vitro gastrointestinal digestion process that includes the brush border membrane peptidases. Competitive ELISA, based on R5 monoclonal antibody, showed that gastrointestinal digestion reduced the immunogenicity of Triticum monococcum gliadins; conversely, the immunogenic potential of Triticum durum gliadins remained almost unchanged by the in vitro digestion. The immune stimulatory activity was also evaluated by detecting the IFN-γ production in gliadin-reactive T-cell lines obtained from the small intestinal mucosa of HLA-DQ2+ celiac disease patients. Interestingly, gastrointestinal digestion markedly reduced the capability of Triticum monococcum gliadins (p <0.05) of both cultivars to activate T cells, while it slightly affected the activity of Triticum durum. In conclusion, our results showed that Triticum durum was almost unaffected by the in vitro gastrointestinal digestion, while Triticum monococcum had a marked sensibility to digestion, thus determining a lower toxicity for celiac disease patients.

Elevated Atmospheric CO2 Concentration Has Limited Effect on Wheat Grain Quality Regardless of Nitrogen Supply

Elevated atmospheric CO₂ concentrations (e[CO₂]) can decrease the grain quality of wheat. However, little information exists concerning interactions between e[CO₂] and nitrogen fertilization on important grain quality traits. To investigate this, a 2-year free air CO₂ enrichment (FACE) experiment was conducted with two CO₂ (393 and 600 ppm) and three (deficiency, adequate, and excess) nitrogen levels. Concentrations of flour proteins (albumins/globulins, gliadins, and glutenins) and key minerals (iron, zinc, and sulfur) and baking quality (loaf volume) were markedly increased by increasing nitrogen levels and varied between years. e[CO₂] resulted in slightly decreased albumin/globulin and total gluten concentration under all nitrogen conditions, whereas loaf volume and mineral concentrations remained unaffected. Two-dimensional gel electrophoresis revealed strong effects of nitrogen supply and year on the grain proteome. Under adequate nitrogen, the grain proteome was affected by e[CO₂] with 19 downregulated and 17 upregulated protein spots. The downregulated proteins comprised globulins but no gluten proteins. e[CO₂] resulted in decreased crude protein concentration at maximum loaf volume. The present study contrasts with other FACE studies showing markedly stronger negative impacts of e[CO₂] on chemical grain quality, and the reasons for that might be differences between genotypes, soil conditions, or the extent of growth stimulation by e[CO₂].

Heat stress effects on source-sink relationships and metabolome dynamics in wheat

Crops such as wheat (Triticum spp.) are predicted to face more frequent exposures to heat stress as a result of climate change. Increasing the yield and sustainability of yield under such stressful conditions has long been a major target of wheat breeding, and this goal is becoming increasingly urgent as the global population increases. Exposure of wheat plants in their reproductive or grain-filling stage to high temperature affects the duration and rate of grain filling, and hence has a negative impact on wheat productivity. Therefore, understanding the plasticity of the response to heat stress that exists between wheat genotypes, especially in source-sink relationships at the reproductive and grain-filling stages, is critical for the selection of germplasm that can maintain high yields under heat stress. A broad understanding of metabolic dynamics and the relationships between metabolism and heat tolerance is required in order to achieve this goal. Here, we review the current literature concerning the effects of heat stress on sink-source relationships in a wide range of wheat genotypes, and highlight the current metabolomic approaches that are used to investigate high temperature responses in wheat.

Proteomic Data Integration Highlights Central Actors Involved in Einkorn (Triticum monococcum ssp. monococcum) Grain Filling in Relation to Grain Storage Protein Composition

Albumins and globulins (AGs) of wheat endosperm represent about 20% of total grain proteins. Some of these physiologically active proteins can influence the synthesis of storage proteins (SPs) (gliadins and glutenins) and consequently, rheological properties of wheat flour and processing. To identify such AGs, data, (published by Bonnot et al., 2017) concerning abundance in 352 AGs and in the different seed SPs during grain filling and in response to different nitrogen (N) and sulfur (S) supply, were integrated with mixOmics R package. Relationships between AGs and SPs were first unraveled using the unsupervised method sparse Partial Least Square, also known as Projection to Latent Structure (sPLS). Then, data were integrated using a supervised approach taking into account the nutrition and the grain developmental stage. We used the block.splda procedure also referred to as DIABLO (Data Integration Analysis for Biomarker discovery using Latent variable approaches for Omics studies). These approaches led to the identification of discriminant and highly correlated features from the two datasets (AGs and SPs) which are not necessarily differentially expressed during seed development or in response to N or S supply. Eighteen AGs were correlated with the quantity of SPs per grain. A statistical validation of these proteins by genetic association analysis confirmed that 5 out of this AG set were robust candidate proteins able to modulate the seed SP synthesis. In conclusion, this latter result confirmed that the integrative strategy is an adequate way to reduce the number of potentially relevant AGs for further functional validation.

Technological Quality and Nutritional Value of Two Durum Wheat Varieties Depend on Both Genetic and Environmental Factors

Durum wheat ( Triticum turgidum L. subsp. durum (Desf.) Husn) is a major food source in Mediterranean countries since it is utilized for the production of pasta, leavened and unleavened breads, couscous, and other traditional foods. The technological and nutritional properties of durum wheat semolina depend mainly on the type of gluten proteins and on their amount, which is a genotype- and environment-dependent trait. Gluten proteins are also responsible for celiac disease (CD), an autoimmune enteropathy with a prevalence of about 0.7-2% in the human population. At this purpose, two Italian durum wheat cultivars, Saragolla and Cappelli, currently used for monovarietal pasta, were chosen to compare (i) the reserve and embryo proteome, (ii) the free and bound phenolics, antioxidant activity, and amino acid composition, and (iii) the content of immunogenic peptides produced after a simulated gastrointestinal digestion. The results obtained from 2 years of field cultivation on average showed a higher amount of gluten proteins, amino acids, and immunogenic peptides in Cappelli. Saragolla showed a higher abundance in bound phenolics, antioxidant enzymes, and stress response proteins in line with its higher antioxidant activity. However, the impact of the year of cultivation, largely depending on varying rainfall regimes through the wheat growth cycle, was significant for most of the parameters investigated. Differences in technological and nutritional characteristics observed between the two cultivars are discussed in relation to the influence of genetic and environmental factors.

Comparative proteomic analysis of durum wheat shoots from modern and ancient cultivars

Durum wheat is widespread cultivated in the Mediterranean basin, where it is used to produce high-quality semolina for pasta. Although over the years local and ancient wheat cultivars have been replaced by new ones, better suited to intensive cultivation, the increasing demand of consumers for nutritional and sensory qualities, as well as their attention to sustainable agronomic practices, renewed the interest toward traditional varieties. In order to fully exploit their agronomical and nutritional potential, a systematic analysis of molecular traits would be desirable. Nowadays, this examination is greatly facilitated by the current availability of high-throughput genomic and proteomic methods, which are integrated with classical measurements on plant physiology. To this purpose, we performed a comparative study on germination performances, hormone level variations, and differential protein representations of three-days germinated shoots of two traditional wheat cultivars from Southern Italy, namely Senatore Cappelli and Saragolla, and the commercial elite variety Svevo. Two-dimensional electrophoresis- and nanoLC-ESI-LIT-MS/MS-based proteomic analysis revealed 45 differentially represented spots, which were associated with 32 non-redundant protein species grouping into storage, stress/defense and metabolism/energy production functional categories. Major differences in the traditional varieties concerned over-representation of glutenins, gamma-gliadin and some enzymes of glycolysis and TCA cycle, as well as a down-representation of proteins involved in the response to stress conditions. These features were here discussed in relation to the hormone profile and the known agronomic features of traditional varieties, as compared to the commercial one.

Metabolic adaptation of wheat grain contributes to a stable filling rate under heat stress

Wheat (Triticum aestivum) is particularly vulnerable to heat stress during the grain filling stage, and this can adversely affect the final yield. However, the underlying physiological and molecular mechanisms are largely unknown. In this study, the effects of heat stress on grain filling were investigated using wheat varieties with different levels of thermotolerance. Decreased grain weights and filling durations, increased protein contents, and stable filling rates across diverse varieties under different heat regimes suggested a general mechanism for heat adaptation. Proteomic analysis identified 309 heat-responsive proteins (HRPs), and revealed a general decrease in protein synthesis components and metabolic proteins, but a significant increase in stress-response proteins and storage proteins. Metabolomic analysis identified 98 metabolites specifically changed by heat stress, and suggested a global decrease in the content of carbohydrate metabolites, an increased content of amino acids, and stable levels of starch synthesis precursors. The energy-consuming HRPs suggested that less energy was channelled into metabolism and protein synthesis, whereas more energy was allocated to the stress response under elevated heat conditions. Collectively, the data demonstrated a widely distributed mechanism for heat adaptation of metabolism, in which the assimilation and energy required for metabolism and protein synthesis are reallocated to heat protection and deposition of reserves, resulting in increased storage protein accumulation and a stable filling rate.

Identification of Early Represented Gluten Proteins during Durum Wheat Grain Development

The time course of biosynthesis and accumulation of storage proteins in developing grains of durum wheat (Triticum turgidum ssp. durum (Desf.) Husn.) pasta-quality reference cv. Svevo was investigated at the protein level for the first time. Seeds were harvested at key kernel developmental stages, namely, 3 (seed increase 3-fold in size), 5 (kernel development, water-ripe stage), 11 (kernel development, water-ripe stage), 16 (kernel full development, water-ripe stage), 21 (milk-ripe stage), and 30 (dough stage) days postanthesis (dpa). Gliadins and glutenins were fractionated according to their different solubility and individually analyzed after fractionation by reversed-phase high performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Proteins were identified by liquid chromatography-tandem mass spectrometry of proteolytic peptides. The α- and γ-gliadin were already detected at 3 dpa. The biosynthesis of high molecular mass glutenin Bx7 was slightly delayed (11 dpa). Most of the gluten proteins accumulated rapidly between 11 and 21 dpa, with a minor further increase up to 30 dpa. The expression pattern of gluten proteins in Triticum durum at the early stages of synthesis provides reference data sets for future applications in crop breeding and growth monitoring.