Molecular mechanisms of HMW glutenin subunits from 1S(l) genome of Aegilops longissima positively affecting wheat breadmaking quality

Development of PCR-based markers for identification of wheat HMW glutenin Glu-1Bx and Glu-1By alleles

BACKGROUND

In common wheat (Triticum aestivum L.), allelic variations in the high-molecular-weight glutenin subunits Glu-B1 locus have important effects on grain end-use quality. The Glu-B1 locus consists of two tightly linked genes encoding x- and y-type subunits that exhibit highly variable frequencies. However, studies on the discriminating markers of the alleles that have been reported are limited. Here, we developed 11 agarose gel-based PCR markers for detecting Glu-1Bx and Glu-1By alleles.

RESULTS

By integrating the newly developed markers with previously published PCR markers, nine Glu-1Bx locus alleles (Glu-1Bx6, Glu-1Bx7, Glu-1Bx7*, Glu-1Bx7 OE, Glu-1Bx13, Glu-1Bx14 (-) , Glu-1Bx14 (+)/Bx20, and Glu-1Bx17) and seven Glu-1By locus alleles (Glu-1By8, Glu-1By8*, Glu-1By9, Glu-1By15/By20, Glu-1By16, and Glu-1By18) were distinguished in 25 wheat cultivars. Glu-1Bx6, Glu-1Bx13, Glu-1Bx14 (+)/Bx20, Glu-1By16, and Glu-1By18 were distinguished using the newly developed PCR markers. Additionally, the Glu-1Bx13 and Glu-1Bx14 (+)/Bx20 were distinguished by insertions and deletions in their promoter regions. The Glu-1Bx6, Glu-1Bx7, Glu-1By9, Glu-1Bx14 (-), and Glu-1By15/By20 alleles were distinguished by using insertions and deletions in the gene-coding region. Glu-1By13, Glu-1By16, and Glu-1By18 were dominantly identified in the gene-coding region. We also developed a marker to distinguish between the two Glu-1Bx14 alleles. However, the Glu-1Bx14 (+) + Glu-1By15 and Glu-1Bx20 + Glu-1By20 allele combinations could not be distinguished using PCR markers. The high-molecular-weight glutenin subunits of wheat varieties were analyzed by ultra-performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the findings were compared with the results of PCR analysis.

CONCLUSIONS

Seven Glu-1Bx and four Glu-1By allele detection markers were developed to detect nine Glu-1Bx and seven Glu-1By locus alleles, respectively. Integrating previously reported markers and 11 newly developed PCR markers improves allelic identification of the Glu-B1 locus and facilitates more effective analysis of Glu-B1 alleles molecular variations, which may improve the end-use quality of wheat.

Effects of Aegilops longissima chromosome 1Sl on wheat bread-making quality in two types of translocation lines

KEY MESSAGE

Two wheat-Ae. longissima translocation chromosomes (1BS·1SlL and 1SlS·1BL) were transferred into three commercial wheat varieties, and the new advanced lines showed improved bread-making quality compared to their recurrent parents. Aegilops longissima chromosome 1Sl encodes specific types of gluten subunits that may positively affect wheat bread-making quality. The most effective method of introducing 1Sl chromosomal fragments containing the target genes into wheat is chromosome translocation. Here, a wheat-Ae. longissima 1BS·1SlL translocation line was developed using molecular marker-assisted chromosome engineering. Two types of translocation chromosomes developed in a previous study, 1BS·1SlL and 1SlS·1BL, were introduced into three commercial wheat varieties (Ningchun4, Ningchun50, and Westonia) via backcrossing with marker-assisted selection. Advanced translocation lines were confirmed through chromosome in situ hybridization and genotyping by target sequencing using the wheat 40 K system. Bread-making quality was found to be improved in the two types of advanced translocation lines compared to the corresponding recurrent parents. Furthermore, 1SlS·1BL translocation lines displayed better bread-making quality than 1BS·1SlL translocation lines in each genetic background. Further analysis revealed that high molecular weight glutenin subunit (HMW-GS) contents and expression levels of genes encoding low molecular weight glutenin subunits (LMW-GSs) were increased in 1SlS·1BL translocation lines. Gliadin and gluten-related transcription factors were also upregulated in the grains of the two types of advanced translocation lines compared to the recurrent parents. This study clarifies the impacts of specific glutenin subunits on bread-making quality and provides novel germplasm resources for further improvement of wheat quality through molecular breeding.

Reducing Nitrogen Rate and Increasing Plant Density Accomplished High Yields with Satisfied Grain Quality of Soft Wheat via Modifying the Free Amino Acid Supply and Storage Protein Gene Expression

In a 2 yr field experiment, we investigated the combined effects of reduced nitrogen (N) rate and increased plant density on the trade-off between the grain protein content (GPC) and the grain yield (GY) in soft wheat cultivars. Reducing N application significantly decreased both GPC and GY; however, to some extent, increasing the top-dressed N ratio and plant density compensated for the GY loss. Optimizing the combination of these three factors (150 kg N ha^-1 with 50% top-dressed N and 360 × 10⁴ plants ha^-1) achieved both the required lower GPC for soft wheat and relatively higher GY compared with the conventional cultivation strategy. In addition, this optimized combination downregulated 11 high-molecular-weight glutenin subunits, 8 low-molecular-weight glutenin subunits, 5 α/β-gliadins, and 2 γ-gliadins in mature grains as identified by data-independent acquisition mass spectrometry. Further analysis indicated that the relatively lower free amino acid content and downregulated expressions of the seed storage protein (SSP) synthesis-related genes in filling grains contributed to the reduction of SSP and GPC. Furthermore, the dilution effect induced by a relatively higher accumulation of starch than proteins also partially explained the reduced GPC. Unlike proteins, grain starch accumulation and content depended more on the soluble sugar availability, rather than on the starch synthesis capacity. These findings provide novel insights on simultaneous improvement in the grain quality and yield of soft wheat through synchronized manipulations of N fertilization and plant density.

The unique disarticulation layer formed in the rachis of Aegilops longissima probably results from the spatial co-expression of Btr1 and Btr2

BACKGROUND AND AIMS

The brittle rachis trait is a feature of many wild grasses, particularly within the tribe Triticeae. Wild Hordeum and Triticum species form a disarticulation layer above the rachis node, resulting in the production of wedge-type dispersal units. In Aegilops longissima, only one or two of the nodes in the central portion of its rachis are brittle. In Triticeae species, the formation of a disarticulation layer above the rachis node requires the co-transcription of the two dominant and complementary genes Btr1 and Btr2. This study aims to establish whether homologues of Btr1 and/or Btr2 underlie the unusual brittle rachis phenotype observed in Ae. longissima.

METHODS

Scanning electron microscopy was used to examine the disarticulation surfaces. Quantitative RT-PCR and RNA in situ hybridization experiments were used to identify gene expression in the immature inflorescence.

KEY RESULTS

Analysis based on scanning electron microscopy was able to demonstrate that the disarticulation surfaces formed in the Ae. longissima rachis are morphologically indistinguishable from those formed in the rachises of wild Hordeum and Triticum species. RNA in situ hybridization showed that in the immature Ae. longissima inflorescence, the intensity of Btr1 transcription varied from high at the rachis base to low at its apex, while that of Btr2 was limited to the nodes in the central to distal portion of the rachis.

CONCLUSIONS

The disarticulation pattern shown by Ae. longissima results from the limitation of Btr1 and Btr2 co-expression to nodes lying in the centre of the rachis.

A null allele of granule bound starch synthase (Wx-B1) may be one of the major genes controlling chapatti softness

Chapatti (unleavened flatbread) is a staple food in northern India and neighboring countries but the genetics behind its processing quality are poorly understood. To understand the genes determining chapatti quality, differentially expressed genes were selected from microarray data of contrasting chapatti cultivars. From the gene and trait association studies, a null allele of granule bound starch synthase (GBSS; Wx-B1) was found to be associated with low amylose content and good chapatti quality. For validation, near-isogenic lines (NILs) of this allele were created by marker assisted backcross (MAB) breeding. Background screening indicated 88.2 to 96.7% background recovery in 16 selected BC3F5 NILs. Processing quality and sensory evaluation of selected NILs indicated improvement in chapatti making quality. Traits that showed improvement were mouthfeel, tearing strength and softness indicating that the Wx-B1 may be one of the major genes controlling chapatti softness.

Contribution to Breadmaking Performance of Two Different HMW Glutenin 1Ay Alleles Expressed in Hexaploid Wheat

Two expressed alleles of the 1Ay high-molecular-weight glutenin subunit (HMW-GS), 1Ay21* and 1AyT1, previously introduced in durum and bread wheat, were separately introgressed into the Australian bread wheat (Triticum aestivum L.) cv. Livingston. The developed lines had different allelic compositions compared to that of the parental cultivar (1Ax1), having either 1Ax21+1Ay21* or 1Ax1+1AyT1 at the Glu-A1 locus. Since 1Ax21 and 1Ax1 are known to have the same effects on quality, differences observed between the two sets of the developed lines are attributed to the two introgressed Ay genes. Yield and agronomic performance of the lines were evaluated in the field, and the protein, dough, and baking quality attributes were evaluated by large-scale quality testing. Results demonstrated that the subunit 1Ay21* increased unextractable polymeric protein by up to 14.3% and improved bread loaf volume by up to 9.2%. On the other hand, subunit 1AyT1 increased total grain protein by up to 9% along with dough elasticity. Furthermore, milling extraction was higher, and flour ash was lower in the 1Ay21* lines compared to the lines integrating 1AyT1. Both sets of the 1Ay introgression lines reduced dough-mixing time compared to the recurrent parent Livingston. The results also showed that 1Ay21* had a higher potential to improve the baking quality than 1AyT1 under the Livingston genetic background. Both alleles showed the potential to be utilized in breeding programs to improve the breadmaking quality.

PDI-Regulated Disulfide Bond Formation in Protein Folding and Biomolecular Assembly

Disulfide bonds play a pivotal role in maintaining the natural structures of proteins to ensure their performance of normal biological functions. Moreover, biological molecular assembly, such as the gluten network, is also largely dependent on the intermolecular crosslinking via disulfide bonds. In eukaryotes, the formation and rearrangement of most intra- and intermolecular disulfide bonds in the endoplasmic reticulum (ER) are mediated by protein disulfide isomerases (PDIs), which consist of multiple thioredoxin-like domains. These domains assist correct folding of proteins, as well as effectively prevent the aggregation of misfolded ones. Protein misfolding often leads to the formation of pathological protein aggregations that cause many diseases. On the other hand, glutenin aggregation and subsequent crosslinking are required for the formation of a rheologically dominating gluten network. Herein, the mechanism of PDI-regulated disulfide bond formation is important for understanding not only protein folding and associated diseases, but also the formation of functional biomolecular assembly. This review systematically illustrated the process of human protein disulfide isomerase (hPDI) mediated disulfide bond formation and complemented this with the current mechanism of wheat protein disulfide isomerase (wPDI) catalyzed formation of gluten networks.

High-Molecular-Weight Glutenin Subunits: Genetics, Structures, and Relation to End Use Qualities

High-molecular-weight glutenin subunits (HMW-GSs) are storage proteins present in the starchy endosperm cells of wheat grain. Encoding the synthesis of HMW-GS, the Glu-1 loci located on the long arms of group 1 chromosomes of the hexaploid wheat (1A, 1B, and 1D) present multiple allelism. In hexaploid wheat cultivars, almost all of them express 3 to 5 HMW-GSs and the 1Ay gene is always silent. Though HMW-GSs are the minor components in gluten, they are crucial for dough properties, and certain HMW-GSs make more positive contributions than others. The HMW-GS acts as a "chain extender" and provides a disulfide-bonded backbone in gluten network. Hydrogen bonds mediated by glutamine side chains are also crucial for stabilizing the gluten structure. In most cases, HMW-GSs with additional or less cysteines are related to the formation of relatively more or less interchain disulfide bonds and HMW-GSs also affect the gluten secondary structures, which in turn impact the end use qualities of dough.

Diversity in Grain, Flour, Amino Acid Composition, Protein Profiling, and Proportion of Total Flour Proteins of Different Wheat Cultivars of North India

Wheat cultivars grown at three different locations in North India were assessed for their variability in kernel and flour characteristics. Protein and the wet and dry gluten contents of the flour varied significantly (p ≤ 0.05) from 9.32 to 12.60%, 23.46 to 43.04%, and from 8.28 to 15.00%, respectively. Wheat varieties exhibited moderate sodium dodecyl sulfate (SDS) sedimentation and solvent retention values. Flour showed a significant (p ≤ 0.05) difference in the amino acid composition. Lysine, having the lowest chemical score, was the first most limiting amino acid in all wheat varieties. The variability of total flour proteins determined by SDS-PAGE showed polymorphism both in the number and intensity of bands, particularly in the molecular weight range of 35.1-42.8 kDa corresponding to the α-, β-, and γ-gliadin/low-molecular-weight glutenin subunit (LMW-GS) region. Pearson's correlation established between the various grain and flour parameters showed a significant correlation, which can result in better end product use.

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.

Genome-wide impacts of alien chromatin introgression on wheat gene transcriptions

Agronomic characteristics and tolerance to biotic and abiotic stresses in hexaploid wheat can be drastically improved through wheat-alien introgression. However, the transcriptional level interactions of introduced alien genes in the wheat genetic background is rarely investigated. In this study, we report the genome-wide impacts of introgressed chromosomes derived from Ae. longissima on gene transcriptions of the wheat landrace Chinese Spring. RNA-seq analyses demonstrated 5.37% and 4.30% of the genes were significantly differentially expressed (DEGs) in CS-Ae. longissima disomic 3S^l#2(3B) substitution line TA3575 and disomic 6S^l#3 addition line TA7548, respectively when compared to CS. In addition, 561 DEGs, including 413 up-regulated and 148 down-regulated or not transcribed genes, were simultaneously impacted by introgressed chromosomes 3S^l#2 and 6S^l#3, which accounts for 41.25% of the DEGs in TA3575 and 38.79% in TA7548. Seventeen DEGs, annotated as R genes, were shared by both introgression lines carrying chromosomes 3S^l#2 and 6S^l#3, which confer resistance to powdery mildew. This study will benefit the understanding of the wheat gene responses as result of alien gene(s) or chromosome intogression and the plant defense response initiated by powdery mildew resistance genes in chromosomes 3S^l#2 and 6S^l#3.

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.

Effects of an Additional Cysteine Residue of Avenin-like b Protein by Site-Directed Mutagenesis on Dough Properties in Wheat (Triticum aestivum L.)

Avenin-like b protein is rich in cysteine residues, providing the possibility to form intermolecular disulfide bonds and then participate in glutenin polymerization. Site-directed mutagenesis was adopted to produce mutant avenin-like b gene encoding mutant avenin-like b protein, in which one tyrosine codon at the C-terminal is substituted by a cysteine codon. Compared with the control lines, both transgenic lines with wild-type and mutant avenin-like b genes demonstrated superior dough properties. While compared within the transgenic lines, the mutant lines showed relative weaker dough strength and decreased sodium-dodecyl-sulfate sedimentation volumes (from 69.7 mL in line WT alb-1 to 41.0 mL in line Mut alb-4). These inferior dough properties were accompanied by the lower contents of large-sized glutenin polymers, the decreased particle diameters of glutenin macropolymer (GMP), due to the lower content of intermolecular β-sheets (from 39.48% for line WT alb-2 to 30.21% for line Mut alb-3) and the varied contents of disulfide bonds (from 137.37 μmol/g for line WT alb-1 to 105.49 μmol/g for line Mut alb-4) in wheat dough. The extra cysteine might alter the original disulfide bond structure, allowing cysteine residue usually involved in an intermolecular disulfide bond to become available for an intrachain disulfide bond. Avenin-like b proteins were detected in glutenin macropolymers, providing further evidence for this protein to participate in the polymerization of glutenin. This is the first time to investigate the effect of a specific cysteine residue in the avenin-like b protein on flour quality.

Cloning and characterization of special HMW glutenin subunit genes from Aegilops longissima L. and their potential for wheat quality improvement

Identification and cloning of new glutenin genes from wheat-related species can provide candidate gene resources for quality improvement of wheat. In this study, ten special high-molecular-weight glutenin subunits (HMW-GS), including five x-type (1S^l2x, 1S^l16x, 1S^l17x, 1S^l23x, and 1S^l25x) and five y-type (1S^l2y, 1S^l6y₁, 1S^l16y, 1S^l17y, and 1S^l23y) from Aegilops longissima L. (S^lS^l, 2n = 2x = 14) were identified, and their complete encoding genes were cloned by allelic-specific polymerase chain reaction (AS-PCR). The deduced amino acid (aa) residues of the x-type subunit genes ranged from 821 aa (2469 bp) to 941 aa (2829 bp), while those of the y-type subunit genes varied from 749 aa (2250 bp) to 771 aa (2361 bp). These special HMW-GS had a longer central repetitive domain with more glutamine repeats and glutamine residues compared to the previously characterized HMW-GS in common wheat, which provided a structural basis for superior gluten quality formation. The authenticity of the four cloned genes were verified by matrix-assisted laser desorption ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). Abundant single-nucleotide polymorphism (SNP) and insertion/deletion (InDel) variations among these genes were identified, which would benefit for developing specific molecular markers used for wheat gluten quality improvement. Phylogenetic analysis revealed that the 1S^l-encoded HMW-GS had close relationships with those from bread wheat, which were divergent from Triticum species at 2.10-10.00 million years ago. Our results indicate that the 1S^l genome contains superior candidate glutenin genes that have potential application values for the improvement of wheat bread making quality.

High-Molecular-Weight Glutenin 1Bx17 and 1By18 Subunits Encoded by Glu-B1i Enhance Rheological Properties and Breadmaking Quality of Wheat Dough

The elasticity of wheat dough is mainly determined by high-molecular-weight glutenin subunits (HMW-GSs) encoded by Glu-1 loci. In this study, we performed the first comprehensive study on the effects of Glu-B1i-encoded 1Bx17 and 1By18 subunits on dough rheological properties and breadmaking quality by using a pair of Glu-B1 near-isogenic lines (NILs) ZM-NIL1 and ZM-NIL2. Comparative analysis of basic quality parameters, rapid visco analyzer (RVA) and farinograph parameters, and C-cell and loaf parameters showed that ZM-NIL2 containing Glu-B1i-encoded 1Bx17 and 1By18 subunits had better dough rheological properties and breadmaking quality than ZM-NIL1 carrying Glu-B1c-encoded 1Bx7 and 1By9 subunits, including significantly increased protein and gluten content, development time and stability, and loaf volume and score. Particularly, 1Bx17 and 1By18 subunits could significantly enhance bread texture, including significant increase in slice brightness, slice area, circumference, cell contrast, cell extension, and cell quantity. These results demonstrate that 1Bx17 and 1By18 subunits have a significant contribution to dough rheological properties and breadmaking quality.

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

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

Nitrogen topdressing timing modifies free amino acids profiles and storage protein gene expression in wheat grain

BACKGROUND

Nitrogen is one basic element of amino acids and grain protein in wheat. In field experiments, wheat plants were subjected to different timing of nitrogen topdressing treatments: at the stages of emergence of the top fifth leaf (TL5), top third leaf (TL3) and top first leaf (TL1) to test the regulatory effects of nitrogen topdressing timing on grain protein quality. The underlying mechanisms were elucidated by clarifying the relationship between proteolysis in vegetative organs and accumulation of amino acids in the endosperm cavity, conversion of amino acids, and storage protein synthesis in endosperm of wheat grain.

RESULTS

Delayed nitrogen topdressing up-regulated gene expression related to nitrogen metabolism and protease synthesis in the flag leaf, followed by more free amino acids being transported to both the cavity and the endosperm from 7 days after anthesis (DAA) to 13 DAA in TL1. TL1 enhanced the conversion between free amino acids in endosperm and upregulated the expression of genes encoding high molecular weight (HMW) and low molecular weight (LMW) subunits and protein disulfide isomerases-like (PDIL) proteins, indicating that the synthesis and folding of glutenin were enhanched by delayed nitrogen topdressing. As a consequense, the content of glutenin macropolymers (GMP) and glutenin increased with delaying nitrogen topdressing.

CONCLUSIONS

The results highlight the relationship between nitrogen remobilization and final grain protein production and suggest that the nitrogen remobilization processes could be a potential target for improving the quality of wheat grain. Additionally, specific gene expression related to nitrogen topdressing was identified, which conferred more detailed insights into underlying mechanism on the modification protein quality.

Deletion of high-molecular-weight glutenin subunits in wheat significantly reduced dough strength and bread-baking quality

BACKGROUND

High-molecular-weight glutenin subunits (HMW-GS) play important roles in the elasticity of dough made from wheat. The HMW-GS null line is useful for studying the contribution of HMW-GS to the end-use quality of wheat.

METHODS

In a previous work, we cloned the Glu-1Ebx gene from Thinopyrum bessarabicum and introduced it into the wheat cultivar, Bobwhite. In addition to lines expressing the Glu-1Ebx gene, we also obtained a transgenic line (LH-11) with all the HMW-GS genes silenced. The HMW-GS deletion was stably inherited as a dominant and conformed to Mendel's laws. Expression levels of HMW-GS were determined by RT-PCR and epigenetic changes in methylation patterns and small RNAs were analyzed. Glutenins and gliadins were separated and quantitated by reversed-phase ultra-performance liquid chromatography. Measurement of glutenin macropolymer, and analysis of agronomic traits and end-use quality were also performed.

RESULTS

DNA methylation and the presence of small double-stranded RNA may be the causes of post-transcriptional gene silencing in LH-11. The accumulation rate and final content of glutenin macropolymer (GMP) in LH-11 were significantly lower than in wild-type (WT) Bobwhite. The total protein content was not significantly affected as the total gliadin content increased in LH-11 compared to WT. Deletion of HMW-GS also changed the content of different gliadin fractions. The ratio of ω-gliadin increased, whereas α/β- and γ-gliadins declined in LH-11. The wet gluten content, sedimentation value, development time and stability time of LH-11 were remarkably lower than that of Bobwhite. Bread cannot be made using the flour of LH-11.

CONCLUSIONS

Post-transcriptional gene silencing through epigenetic changes and RNA inhibition appear to be the causes for the gene expression deficiency in the transgenic line LH-11. The silencing of HMW-GW in LH-11 significantly reduced the dough properties, GMP content, wet gluten content, sedimentation value, development time and stability time of flour made from this wheat cultivar. The HMW-GS null line may provide a potential material for biscuit-making because of its low dough strength.

Effects of water deficit on breadmaking quality and storage protein compositions in bread wheat (Triticum aestivum L.)

BACKGROUND

Water deficiency affects grain proteome dynamics and storage protein compositions, resulting in changes in gluten viscoelasticity. In this study, the effects of field water deficit on wheat breadmaking quality and grain storage proteins were investigated.

RESULTS

Water deficiency produced a shorter grain-filling period, a decrease in grain number, grain weight and grain yield, a reduced starch granule size and increased protein content and glutenin macropolymer contents, resulting in superior dough properties and breadmaking quality. Reverse phase ultra-performance liquid chromatography analysis showed that the total gliadin and glutenin content and the accumulation of individual components were significantly increased by water deficiency. Two-dimensional gel electrophoresis detected 144 individual storage protein spots with significant accumulation changes in developing grains under water deficit. Comparative proteomic analysis revealed that water deficiency resulted in significant upregulation of 12 gliadins, 12 high-molecular-weight glutenin subunits and 46 low-molecular-weight glutenin subunits. Quantitative real-time polymerase chain reaction analysis revealed that the expression of storage protein biosynthesis-related transcription factors Dof and Spa was upregulated by water deficiency.

CONCLUSION

The present results illustrated that water deficiency leads to increased accumulation of storage protein components and upregulated expression of Dof and Spa, resulting in an improvement in glutenin strength and breadmaking quality. © 2018 Society of Chemical Industry.

Molecular cloning and functional characterization of two novel high molecular weight glutenin subunit genes in Aegilops markgrafii

The high molecular weight glutenin subunits (HMW-GS) in bread wheat are major determinants of the viscoelastic properties of dough and the end-use quality of wheat flour. Two novel HMW-GSs, 1Cx1.1 and 1Cy9.1, from the diploid species Aegilops markgrafii (CC) were identified in the present study. The corresponding open-reading frames of the genes of 1Cx1.1 and 1Cy9.1 were isolated and sequenced using allele-specific polymerase chain reaction. Sequence comparison demonstrated that the HMW-GSs from Ae. markgrafii possess a similar primary structure to the homologous proteins in wheat and related species. A tandem tripeptide exists in the central repetitive domain of 1Cx1.1, and this unique structure is very rare in the HMW-GSs of other genomes. To confirm the authenticity of these isolated endogenous HMW-GS, the heterologous proteins produced by removing the signal peptides expressed by E. coli exhibited the same electrophoretic mobility as the native proteins. Subsequently, the single protein was purified at a sufficient scale for incorporation into flour to performsodium dodecyl sulphate (SDS) sedimentation testing. Notably, the SDS sedimentation volume was less with the addition of 1Cx1.1 than it was with 1Cy9.1.

Development of a wheat-Aegilops searsii substitution line with positively affecting Chinese steamed bread quality

A wheat-Aegilops searsii substitution line GL1402, in which chromosome 1B was substituted with 1S^s from Ae. searsii, was developed and detected using SDS-PAGE and GISH. The SDS-PAGE analysis showed that the HMW-GS encoded by the Glu-B1 loci of Chinese Spring was replaced by the HMW-GS encoded by the Glu-1S^s loci of Ae. searsii. Glutenin macropolymer (GMP) investigation showed that GL1402 had a much higher GMP content than Chinese Spring did. A dough quality comparison of GL1402 and Chinese Spring indicated that GL1402 showed a significantly higher protein content and middle peak time (MPT), and a smaller right peak slope (RPS). Quality tests of Chinese steamed bread (CSB) showed that the GL1402 also produced good steamed bread quality. These results suggested that the substitution line is a valuable breeding material for improving the wheat processing quality.

Interspecific and intergeneric hybridization as a source of variation for wheat grain quality improvement

The hybridization events with wild relatives and old varieties are an alternative source for enlarging the wheat quality variability. This review describes these process and their effects on the technological and nutritional quality. Wheat quality and its end-uses are mainly based on variation in three traits: grain hardness, gluten quality and starch. In recent times, the importance of nutritional quality and health-related aspects has increased the range of these traits with the inclusion of other grain components such as vitamins, fibre and micronutrients. One option to enlarge the genetic variability in wheat for all these components has been the use of wild relatives, together with underutilised or neglected wheat varieties or species. In the current review, we summarise the role of each grain component in relation to grain quality, their variation in modern wheat and the alternative sources in which wheat breeders have found novel variation.

Development of a set of PCR markers specific to Aegilops longissima chromosome arms and application in breeding a translocation line

Transcriptome data were used to develop 134 Aegilops longissima specific PCR markers and their comparative maps were constructed by contrasting with the homologous genes in the wheat B genome. Three wheat- Ae. longissima 1BL·1S ^l S translocation lines were identified using the correspondence markers. Aegilops longissima is an important wild species of common wheat that harbors many genes that can be used to improve various traits of common wheat (Triticum aestivum L.). To efficiently transfer the traits conferred by these Ae. longissima genes into wheat, we sequenced the whole expression transcript of Ae. longissima. Using the transcriptome data, we developed 134 specific polymerase chain reaction markers located on the 14 chromosome arms of Ae. longissima. These novel molecular markers were assigned to specific chromosome locations based on a comparison with the homologous genes in the B genome of wheat. Annotation of these genes showed that most had functions related to metabolic processes, hydrolase activity, or catalytic activity. Additionally, we used these markers to identify three wheat-Ae. longissima 1BL·1S^lS translocation lines in somatic variation populations resulting from a cross between wheat cultivar Westonia and a wheat-Ae. longissima substitution line 1S^l(1B). The translocation lines had several low molecular weight glutenin subunits encoding genes beneficial to flour processing quality that came from Ae. longissima 1S^lS. The three translocation lines were also confirmed by genomic in situ hybridization. These translocation lines will be further evaluated for potential quality improvement of bread-making properties of wheat.

Rapid Development and Characterization of Chromosome Specific Translocation Line of Thinopyrum elongatum with Improved Dough Strength

The protein content and its type are principal factors affecting wheat (Triticum aestivum) end product quality. Among the wheat proteins, glutenin proteins, especially, high molecular weight glutenin subunits (HMW-GS) are major determinants of processing quality. Wheat and its primary gene pool have limited variation in terms of HMW-GS alleles. Wild relatives of wheat are an important source of genetic variation. For improvement of wheat processing quality its wild relative Thinopyrum elongatum with significant potential was utilized. An attempt was made to replace Th. elongatum chromosome long arm (1EL) carrying HMW-GS genes related to high dough strength with chromosome 1AL of wheat with least or negative effect on dough strength while retaining the chromosomes 1DL and 1BL with a positive effect on bread making quality. To create chromosome specific translocation line [1EL(1AS)], double monosomic of chromosomes 1E and 1A were created and further crossed with different cultivars and homoeologous pairing suppressor mutant line PhI . The primary selection was based upon glutenin and gliadin protein profiles, followed by sequential genomic in situ hybridization (GISH) and fluorescent in situ hybridization (FISH). These steps significantly reduced time, efforts, and economic cost in the generation of translocation line. In order to assess the effect of translocation on wheat quality, background recovery was carried out by backcrossing with recurrent parent for several generations and then selfing while selecting in each generation. Good recovery of parent background indicated the development of almost near isogenic line (NIL). Morphologically also translocation line was similar to recipient cultivar N61 that was further confirmed by seed storage protein profiles, RP-HPLC and scanning electron microscopy. The processing quality characteristics of translocation line (BC4F6) indicated significant improvement in the gluten performance index (GPI), dough mixing properties, dough strength, and extensibility. Our work aims to address the challenge of limited genetic diversity especially at chromosome 1A HMW-GS locus. We report successful development of chromosome 1A specific translocation line of Th. elongatum in wheat with improved dough strength.

Development of a new set of molecular markers for examining Glu-A1 variants in common wheat and ancestral species

In common wheat (Triticum aestivum L.), allelic variations of Glu-A1 locus have important influences on grain end-use quality. Among the three Glu-A1 alleles, Glu-A1a and -A1b encode the high-molecular-weight glutenin subunits (HMW-GSs) 1Ax1 and 1Ax2*, respectively, whereas Glu-A1c does not specify any subunit. Here, we detected a total of 11 Glu-A1 locus haplotypes (H1 to H11) in three wheat species, by developing and using a new set of DNA markers (Xrj5, Xid3, Xrj6, Xid4 and Xrj7). The main haplotypes found in the diploid wheat T. urartu were H1, H4, H5 and H6, with H1 and H4 expressing both 1Ax and 1Ay subunits. The major haplotypes revealed for tetraploid wheat (T. turgidum) were H1, H8 and H9, with the lines expressing both 1Ax and 1Ay belonging to H1, H4 or H7. Four major haplotypes (H1, H9, H10 and H11) were discovered in common wheat, with Glu-A1a associated with H1 and H8, Glu-A1b with H10 or H11, and Glu-A1c with H9. The Glu-A1 locus haplotypes and the new set of DNA markers have potential to be used for more effectively studying and utilizing the molecular variations of Glu-A1 to improve the end-use quality of common wheat are discussed.

Comparative Phosphoproteomic Analysis under High-Nitrogen Fertilizer Reveals Central Phosphoproteins Promoting Wheat Grain Starch and Protein Synthesis

Nitrogen (N) is a macronutrient important for plant growth and development. It also strongly influences starch and protein synthesis, closely related to grain yield and quality. We performed the first comparative phosphoproteomic analysis of developing wheat grains in response to high-N fertilizer. Physiological and biochemical analyses showed that application of high-N fertilizer resulted in significant increases in leaf length and area, chlorophyll content, the activity of key enzymes in leaves such as nitrate reductase (NR), and in grains such as sucrose phosphate synthase (SPS), sucrose synthase (SuSy), and ADP glucose pyrophosphorylase (AGPase). This enhanced enzyme activity led to significant improvements in starch content, grain yield, and ultimately, bread making quality. Comparative phosphoproteomic analysis of developing grains under the application of high-N fertilizer performed 15 and 25 days post-anthesis identified 2470 phosphosites among 1372 phosphoproteins, of which 411 unique proteins displayed significant changes in phosphorylation level (>2-fold or <0.5-fold). These phosphoproteins are involved mainly in signaling transduction, starch synthesis, energy metabolism. Pro-Q diamond staining and Western blotting confirmed our phosphoproteomic results. We propose a putative pathway to elucidate the important roles of the central phosphoproteins regulating grain starch and protein synthesis. Our results provide new insights into the molecular mechanisms of protein phosphorylation modifications involved in grain development, yield and quality formation.

Identification of drought stress related proteins from 1Sl(1B) chromosome substitution line of wheat variety Chinese Spring

BACKGROUND

Wheat, one of the most important crops, has a detrimental effect on both yield and quality under drought stress. As our preliminary experiment showed that the Chinese Spring wheat-Aegilops longissima chromosome substitution line CS-1Sl (1B) had a better drought tolerance than CS, the substitution line CS-1Sl(1B) was used to identify drought stress related proteins by means of a comparative proteome approach in this work. Our present study aimed to explore the gene resources for drought resistance in 1Sl genome.

RESULT

Our results showed that drought stress induced downregulation of relative water and chlorophyll contents and the upregulation of proline content, and further influencing grain filling shortening and significant decrease of plant height, B-type starch granule numbers, grain number and weight. In total, 25 grain albumin and globulin protein spots were found to be specifically encoded by the 1Sl chromosome. In addition, 17 protein spots respected 13 unique proteins were identified by MALDI-TOF/TOF MS, which were mainly involved in adverse defense and gluten quality. Among them, ascorbate peroxidase, serpin-Z2B and alpha-amylase/trypsin inhibitor were upregulated under drought stress. These proteins play important roles in plant drought defenses through various metabolic pathways.

CONCLUSION

Our results indicate that the 1Sl chromosome of Aegilops longissima has potential gene resources that could be useful for improving wheat drought resistance.

Chromosome Specific Substitution Lines of Aegilops geniculata Alter Parameters of Bread Making Quality of Wheat

Wheat cultivars with wide introgression have strongly impacted global wheat production. Aegilops geniculata (M^gU^g) is an important wild relative with several useful traits that can be exploited for wheat improvement. Screening of Ae. geniculata addition lines indicated a negative effect of 1U^g and the positive effect of 1M^g chromosome on wheat dough strength. Negative effect of 1U^g is probably associated with variation in number and position of the tripeptide repeat motif in the high molecular weight glutenin (HMW-G) gene. To utilize the positive potential of 1M^g chromosome, three disomic substitution lines (DSLs) 1M^g(1A), 1M^g(1B) and 1M^g(1D) were created. These lines were characterized for morphological, cytogenetic properties and biochemical signatures using FISH, 1D-, 2D-PAGE and RP-HPLC. Contribution of wheat 1A, 1B and 1D chromosomes towards dough mixing and baking parameters, chapatti quality, Fe/Zn content and glume color were identified. Observed order of variation in the dough mixing and baking parameters {1M^g(1D) ≤wheat ≤1M^g(1B) ≤1M^g(1A)} indicated that chromosome specific introgression is desirable for best utilization of wild species’ potential.

Transfer of HMW glutenin subunits from Aegilops kotschyi to wheat through radiation hybridization

High molecular weight glutenin subunits (HMWGS) are responsible for dough elasticity and bread making quality of bread wheat. Related wild non-progenitor species, Aegilops kotschyi possesses higher molecular weight x and y glutenin subunits than the bread wheat cultivars. A wheat-Aegilops substitution line with 1U chromosome was used for the transfer of (HMWGS) of 1U to wheat by using pollen radiation hybridization approach. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiling showed different patterns of allelic variations with either the presence or absence of HMWGS, Glu-1A (1, null), Glu-1B (7, 7 + 8, 17 + 18) and Glu-1D (5 + 10, 2 + 12, null). The pollen irradiated wheat-Aegilops derivatives, B-56-1-4-2, B-56-1-4-3, B-14-1 and B-14-2 with Glu1Ux and 1Uy and absence or presence of some Glu-1A and Glu-1B HMWGS showed high micro SDS sedimentation test (MST) values while B-16-1 and B-16-2 had moderate MST values and high protein content. However, B-58-3 with transfer of Glu-1Ux + 1Uy for Glu-1D showed very low MST values indicating that Glu-1Ux + 1Uy enhance MST value only in the presence of Glu1D HMWGS. The transfer/substitution of alien HMW-GS for Glu-1A and or Glu-1B loci only can lead to improved bread making quality of wheat.

Harnessing Diversity in Wheat to Enhance Grain Yield, Climate Resilience, Disease and Insect Pest Resistance and Nutrition Through Conventional and Modern Breeding Approaches

Current trends in population growth and consumption patterns continue to increase the demand for wheat, a key cereal for global food security. Further, multiple abiotic challenges due to climate change and evolving pathogen and pests pose a major concern for increasing wheat production globally. Triticeae species comprising of primary, secondary, and tertiary gene pools represent a rich source of genetic diversity in wheat. The conventional breeding strategies of direct hybridization, backcrossing and selection have successfully introgressed a number of desirable traits associated with grain yield, adaptation to abiotic stresses, disease resistance, and bio-fortification of wheat varieties. However, it is time consuming to incorporate genes conferring tolerance/resistance to multiple stresses in a single wheat variety by conventional approaches due to limitations in screening methods and the lower probabilities of combining desirable alleles. Efforts on developing innovative breeding strategies, novel tools and utilizing genetic diversity for new genes/alleles are essential to improve productivity, reduce vulnerability to diseases and pests and enhance nutritional quality. New technologies of high-throughput phenotyping, genome sequencing and genomic selection are promising approaches to maximize progeny screening and selection to accelerate the genetic gains in breeding more productive varieties. Use of cisgenic techniques to transfer beneficial alleles and their combinations within related species also offer great promise especially to achieve durable rust resistance.

Comprehensive Identification and Bread-Making Quality Evaluation of Common Wheat Somatic Variation Line AS208 on Glutenin Composition

High molecular weight glutenin subunits (HMW-GSs) are important seed storage proteins in wheat (Triticum aestivum) that determine wheat dough elasticity and processing quality. Clarification of the defined effectiveness of HMW-GSs is very important to breeding efforts aimed at improving wheat quality. To date, there have no report on the expression silencing and quality effects of 1Bx20 and 1By20 at the Glu-B1 locus in wheat. A wheat somatic variation line, AS208, in which both 1Bx20 and 1By20 at Glu-B1 locus were silenced, was developed recently in our laboratory. Evaluation of agronomic traits and seed storage proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and reversed-phase high performance liquid chromatography (RP-HPLC) indicated that AS208 was highly similar to its parental cultivar Lunxuan987 (LX987), with the exception that the composition and expression of HMW-GSs was altered. The 1Bx20 and 1By20 in AS208 were further identified to be missing by polymerase chain reaction (PCR) and quantitative real-time RT-PCR (qRT-PCR) assays. Based on the PCR results for HMW-GS genes and their promoters in AS208 compared with LX987, 1Bx20 and 1By20 were speculated to be deleted in AS208 during in vitro culture. Quality analysis of this line with Mixograph, Farinograph, and Extensograph instruments, as well as analysis of bread-making quality traits, demonstrated that the lack of the genes encoding 1Bx20 and 1By20 caused various negative effects on dough processing and bread-making quality traits, including falling number, dough stability time, mixing tolerance index, crude protein values, wet gluten content, bread size, and internal cell structure. AS208 can potentially be used in the functional dissection of other HMW-GSs as a plant material with desirable genetic background, and in biscuit making industry as a high-quality weak gluten wheat source.

Molecular cloning and potential function prediction of homologous SOC1 genes in tree peony

KEY MESSAGE

The central flower integrator PsSOC1 was isolated and its expression profiles were analyzed; then the potential function of PsSOC1 in tree peony was postulated. The six flowering genes PrSOC1, PdSOC1, PsSOC1, PsSOC1-1, PsSOC1-2, and PsSOC1-3 were isolated from Paeonia rockii, Paeonia delavayi, and Paeonia suffruticosa, respectively. Sequence comparison analysis showed that the six genes were highly conserved and shared 99.41% nucleotide identity. Further investigation suggested PsSOC1 was highly homologous to the floral integrators, SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), from Arabidopsis. Phylogenetic analysis showed that the SOC1 protein clustering has family specificity and PsSOC1 has a close relationship with homologous SOC1 from Asteraceae species. The studies of PsSOC1's expression patterns in different buds and flower buds, and vegetative organs indicated that PsSOC1 could express in both vegetative and reproductive organs. While the expression of PsSOC1 in different developmental stages of buds was different; high expression levels of PsSOC1 occurred in the bud at the bud sprouting stage and the type I aborted the flower bud. PsSOC1 expression was also shown to be affected by gibberellins (GA), low temperature, and photoperiod. One of the pathways that regulates tree peony flowering may be the GA-inductive pathway. Ectopic expression of PsSOC1 in tobacco demonstrated that greater PsSOC1 expression in the transgenic tobacco plants not only promoted plant growth, but also advanced the flowering time. Finally, the potential function of PsSOC1 in tree peony was postulated.

Deletion of the low-molecular-weight glutenin subunit allele Glu-A3a of wheat (Triticum aestivum L.) significantly reduces dough strength and breadmaking quality

BACKGROUND

Low-molecular-weight glutenin subunits (LMW-GS), encoded by Glu-3 complex loci in hexaploid wheat, play important roles in the processing quality of wheat flour. To date, the molecular characteristics and effects on dough quality of individual Glu-3 alleles and their encoding proteins have been poorly studied. We used a Glu-A3 deletion line of the Chinese Spring (CS-n) wheat variety to conduct the first comprehensive study on the molecular characteristics and functional properties of the LMW-GS allele Glu-A3a.

RESULTS

The Glu-A3a allele at the Glu-A3 locus in CS and its deletion in CS-n were identified and characterized by proteome and molecular marker methods. The deletion of Glu-A3a had no significant influence on plant morphological and yield traits, but significantly reduced the dough strength and breadmaking quality compared to CS. The complete sequence of the Glu-A3a allele was cloned and characterized, which was found to encode a B-subunit with longer repetitive domains and an increased number of α-helices. The Glu-A3a-encoded B-subunit showed a higher expression level and accumulation rate during grain development. These characteristics of the Glu-A3a allele could contribute to achieving superior gluten quality and demonstrate its potential application to wheat quality improvement. Furthermore, an allele-specific polymerase chain reaction (AS-PCR) marker for the Glu-A3a allele was developed and validated using different bread wheat cultivars, including near-isogenic lines (NILs) and recombinant inbred lines (RILs), which could be used as an effective molecular marker for gluten quality improvement through marker-assisted selection.

CONCLUSIONS

This work demonstrated that the LMW-GS allele Glu-A3a encodes a specific LMW-i type B-subunit that significantly affects wheat dough strength and breadmaking quality. The Glu-A3a-encoded B-subunit has a long repetitive domain and more α-helix structures as well as a higher expression level and accumulation rate during grain development, which could facilitate the formation of wheat with a stronger dough structure and superior breadmaking quality.

High-level expression of LMW-GS and α-gliadin genes promoted by the expressed tag sequence of 5' end in Escherichia coli

Wheat storage protein genes, especially low molecular weight glutenin subunit (LMW-GS) and gliadin genes are difficult to be expressed in Escherichiacoli, mainly due to the presence of highly repetitive sequences. In order to establish a high efficiency expression system for these genes, five different expression plasmids combining with 9 genes, viz. 6 LMW-GS and 3 α-gliadin genes isolated from common wheat and related species, were studied for heterologous expression in E. coli. In this study, when an expressed tag sequence encoding signal peptide, His-S or GST-tag was fused to the 5' end of LMW-GS or gliadin gene as the leading sequence, all recombination genes could be stably expressed at a high level. On the contrast, as expected, the inserted genes encoding mature protein failed without an expressed tag sequence. This result indicated that using expressed tag sequences as leading sequences could promote LMW-GS and gliadin genes to be well expressed in E. coli. Further transcriptional analysis by quantitative real-time PCR (qRT-PCR) showed transcription levels of recombination genes (e.g. GST-Glutenin, His-S-Glutenin and SP(∗)-His-Glutenin) were 4-fold to 33-fold higher than those of the LMW-GS genes, which suggested these expressed tag sequences might play an important role in stimulating transcription. The possible molecular mechanism under this phenomenon was discussed.

Molecular characterization and expression profiling of the protein disulfide isomerase gene family in Brachypodium distachyon L

Protein disulfide isomerases (PDI) are involved in catalyzing protein disulfide bonding and isomerization in the endoplasmic reticulum and functions as a chaperone to inhibit the aggregation of misfolded proteins. Brachypodium distachyon is a widely used model plant for temperate grass species such as wheat and barley. In this work, we report the first molecular characterization, phylogenies, and expression profiles of PDI and PDI-like (PDIL) genes in B. distachyon in different tissues under various abiotic stresses. Eleven PDI and PDIL genes in the B. distachyon genome by in silico identification were evenly distributed across all five chromosomes. The plant PDI family has three conserved motifs that are involved in catalyzing protein disulfide bonding and isomerization, but a different exon/intron structural organization showed a high degree of structural differentiation. Two pairs of genes (BdPDIL4-1 and BdPDIL4-2; BdPDIL7-1 and BdPDIL7-2) contained segmental duplications, indicating each pair originated from one progenitor. Promoter analysis showed that Brachypodium PDI family members contained important cis-acting regulatory elements involved in seed storage protein synthesis and diverse stress response. All Brachypodium PDI genes investigated were ubiquitously expressed in different organs, but differentiation in expression levels among different genes and organs was clear. BdPDIL1-1 and BdPDIL5-1 were expressed abundantly in developing grains, suggesting that they have important roles in synthesis and accumulation of seed storage proteins. Diverse treatments (drought, salt, ABA, and H₂O₂) induced up- and down-regulated expression of Brachypodium PDI genes in seedling leaves. Interestingly, BdPDIL1-1 displayed significantly up-regulated expression following all abiotic stress treatments, indicating that it could be involved in multiple stress responses. Our results provide new insights into the structural and functional characteristics of the plant PDI gene family.