Puroindoline genes introduced into durum wheat reduce milling energy and change milling behavior similar to soft common wheats

Novel quality features to expand durum wheat applications

Durum wheat represents a staple food in the human diet owing to its nutritional and technological features. In comparison to common wheat, durum wheat has higher tolerance to biotic and abiotic stresses. However, its production and culinary uses are limited compared to common wheat. Therefore, significant attention was attributed to upgrading the key quality of durum wheat (i.e., hardness, protein, starch and color). This review intends to put the spotlight on the modification of these properties to create new functionalities suiting a wider range of food applications based on critical compilation of scientific publications. Targeting specific genes has been shown to be a valuable strategy to design novel wheat varieties with higher nutritional value (e.g., high amylose), improved technological properties (e.g., higher glutenin content), attractive appearance (e.g., colored wheat) and new uses (e.g., soft durum wheat for breadmaking). Further efforts are still needed to find efficient ways to stabilize and maintain these properties. © 2022 Society of Chemical Industry.

Characterization and Differentiation of Grain Proteomes from Wild-Type Puroindoline and Variants in Wheat

Premium wheat with a high end-use quality is generally lacking in China, especially high-quality hard and soft wheat. Pina-D1 and Pinb-D1 (puroindoline genes) influence wheat grain hardness (i.e., important wheat quality-related parameter) and are among the main targets in wheat breeding programs. However, the mechanism by which puroindoline genes control grain hardness remains unclear. In this study, three hard wheat puroindoline variants (MY26, GX3, and ZM1) were compared with a soft wheat variety (CM605) containing the wild-type puroindoline genotype. Specifically, proteomic methods were used to screen for differentially abundant proteins (DAPs). In total, 6253 proteins were identified and quantified via a high-throughput tandem mass tag quantitative proteomic analysis. Of the 208 DAPs, 115, 116, and 99 proteins were differentially expressed between MY26, GX3, and ZM1 (hard wheat varieties) and CM605, respectively. The cluster analysis of protein relative abundances divided the proteins into six clusters. Of these proteins, 67 and 41 proteins were, respectively, more and less abundant in CM605 than in MY26, GX3, and ZM1. Enrichment analyses detected six GO terms, five KEGG pathways, and five IPR terms that were shared by all three comparisons. Furthermore, 12 proteins associated with these terms or pathways were found to be differentially expressed in each comparison. These proteins, which included cysteine proteinase inhibitors, invertases, low-molecular-weight glutenin subunits, and alpha amylase inhibitors, may be involved in the regulation of grain hardness. The candidate genes identified in this study may be relevant for future analyses of the regulatory mechanism underlying grain hardness.

Increasing the Versatility of Durum Wheat through Modifications of Protein and Starch Composition and Grain Hardness

Although durum wheat (Triticum durum L. ssp. durum Desf.) has traditionally been used to make a range of food products, its use has been restricted due to the absence of the D-genome glutenin proteins, the relatively low variability in starch composition, and its very hard grain texture. This review focuses on the manipulation of the starch and protein composition and modification of the hardness of durum wheat in order to improve its technological and nutritional value and expand its utilization for application to a wider number of end products. Starch is composed of amylopectin and amylose in a 3:1 ratio, and their manipulation has been explored for achieving starch with modified composition. In particular, silencing of the genes involved in amylose and amylopectin synthesis has made it possible to isolate durum wheat lines with amylose content varying from 2–3% up to 75%. This has created opportunities for new products with different properties and enhanced nutritional value. Durum-made bread has generally inferior quality to bread made from common wheat. Attempts to introduce the Glu-D1 subunits 1Dx5 + 1Dy10 and 1Dx2 + 1Dy12 produced stronger dough, but the former produced excessively strong, inelastic doughs, and loaf volume was either inferior or not affected. In contrast, the 1Dx2 + 1Dy12 sometimes improved bread loaf volume (LV) depending on the glutenin subunit background of the genotype receiving these genes. Further breeding and selection are needed to improve the dough extensibility to allow higher LV and better texture. The versatility of durum wheat has been greatly expanded with the creation of soft-textured durum via non-GMO introgression means. This soft durum mills like soft hexaploid wheat and has similar baking properties. The pasta quality is also not diminished by the soft-textured kernels. The Glu-D1 locus containing the subunits 1Dx2 + 1Dy12 has also been introgressed to create higher quality soft durum bread.

NanoUPLC-MSE reveals differential abundance of gluten proteins in wheat flours of different technological qualities

Gluten proteins contribute to the rheological properties of dough. Mass spectrometric techniques help to understand the contribution of these proteins to the quality of the end product. This work aimed to apply modern proteomic techniques to characterize and provide a better understanding of gluten proteins in wheat flours of different technological qualities. Nine Brazilian wheat flours (Triticum aestivum) classified by rheological gluten force were used to extract the proteins. Extracts were pooled together by technological qualities in low (LW), medium (MD), and superior (SP). Peptides were analyzed by nanoUPLC and mass spectrometry multiplex method (MS^E). Collectively, 3545 peptides and 1297 proteins were identified, and 116 proteins were found differentially abundant. Low molecular weight glutenin subunits (LMW-GS) were found up-regulated only in SP samples. Proteins related to wheat grain hardness, such as puroindoline-A, were found in significant concentration in LW samples. After domain prediction, LW presented a different pattern with a lower abundance of functional domains, and SP presented chaperones, known to be involved in adequate folding of the storage proteins. NanoUPLC-MS^E was efficient in analyzing and distinguishing the proteomic pattern of wheat flours from different qualities, pointing out the differentially abundant gluten proteins and providing a better understanding of wheat flour quality. SIGNIFICANCE: Common wheat is one of the most important staple food sources in the world. The improvement and comprehension of wheat quality has been a major objective of plant breeders and cereal chemists. Our findings highlighted the application of a modern proteomic approach to obtain a better understanding of the impact of gluten proteins on the technological quality of different wheat flours. The obtained data revealed different abundances of wheat quality-related proteins in superior quality flours when compared with samples of low rheological properties. In addition, multivariate statistical analysis clearly distinguished the flours of different qualities. This work contributes to the consolidation of research in the field of wheat technological quality.

Normal-Phase HPLC-ELSD to Compare Lipid Profiles of Different Wheat Flours

Normal-phase high-performance liquid chromatography (HPLC) is widely used in combination with evaporative light scattering detection (ELSD) for separating and detecting lipids in various food samples. ELSD responses of different lipids were evaluated to elucidate the possibilities and challenges associated with quantification by means of HPLC-ELSD. Not only the number and type of polar functional groups but also the chain length and degree of unsaturation of (free or esterified) fatty acids (FAs) had a significant effect on ELSD responses. Tripalmitin and trilinolein yielded notably different ELSD responses, even if their constituting free FAs produced identical responses. How FA structure impacts ELSD responses of free FAs is thus not predictive for those of triacylglycerols and presumably other lipids containing esterified FAs. Because ELSD responses of lipids depend on the identity of the (esterified) FA(s) which they contain, fully accurate lipid quantification with HPLC-ELSD is challenging and time-consuming. Nonetheless, HPLC-ELSD is a good and fast technique to semi-quantitatively compare the levels of different lipid classes between samples of comparable FA composition. In this way, lipid profiles of different flours from near-isogenic wheat lines could be compared.

Toward the Genetic Basis and Multiple QTLs of Kernel Hardness in Wheat

Kernel hardness is one of the most important single traits of wheat seed. It classifies wheat cultivars, determines milling quality and affects many end-use qualities. Starch granule surfaces, polar lipids, storage protein matrices and Puroindolines potentially form a four-way interaction that controls wheat kernel hardness. As a genetic factor, Puroindoline polymorphism explains over 60% of the variation in kernel hardness. However, genetic factors other than Puroindolines remain to be exploited. Over the past two decades, efforts using population genetics have been increasing, and numerous kernel hardness-associated quantitative trait loci (QTLs) have been identified on almost every chromosome in wheat. Here, we summarize the state of the art for mapping kernel hardness. We emphasize that these steps in progress have benefitted from (1) the standardized methods for measuring kernel hardness, (2) the use of the appropriate germplasm and mapping population, and (3) the improvements in genotyping methods. Recently, abundant genomic resources have become available in wheat and related Triticeae species, including the high-quality reference genomes and advanced genotyping technologies. Finally, we provide perspectives on future research directions that will enhance our understanding of kernel hardness through the identification of multiple QTLs and will address challenges involved in fine-tuning kernel hardness and, consequently, food properties.

The antimicrobial properties of the puroindolines, a review

Antimicrobial proteins, and especially antimicrobial peptides (AMPs) hold great promise in the control of animal and plant diseases with low risk of pathogen resistance. The two puroindolines, a and b, from wheat control endosperm softness of the wheat caryopsis (grain), but have also been shown to inhibit the growth and kill various bacteria and fungi, while showing little toxicity to erythrocytes. Puroindolines are small (~ 13 kDa) amphipathic proteins with a characteristic tryptophan-rich domain (TRD) that is part of an 18 or 19 amino acid residue loop subtended by a disulfide bond. This review presents a brief history of the puroindolines, their physical-chemical characteristics, their interaction with lipids and membranes, and their activity as antimicrobial proteins and AMPs. In this latter context, the use of the TRDs of puroindoline a and b in puroindoline AMP function is reviewed. The activity of puroindoline a and b and their AMPs appear to act through similar but somewhat different modes, which may involve membrane binding, membrane disruption and ion channel formation, and intra-cellular nucleic acid binding and metabolic disruption. Natural and synthetic mutants have identified key elements of the puroindolines for antimicrobial activity.

Expression of Puroindoline a in Durum Wheat Affects Milling and Pasting Properties

Durum wheat has limited culinary utilizations partly due to its extremely hard kernel texture. Previously, we developed transgenic durum wheat lines with expression of the wildtype Puroindoline a (Pina) and characterized PINA's effects on kernel hardness, total flour yield and dough mixing properties in durum wheat. The medium-hard kernel texture is potentially useful for exploring culinary applications of durum wheat. In the present study, we examined the milling parameters and flour attributes of the transgenic lines, including particle size distribution, damaged starch and water binding capacity. PINA expression results in increased break and reduction flour yield but decreased shorts. PINA expression also leads to finer flour particles and decreased starch damage. Interestingly, PINA transgenic lines showed increased peak viscosity and breakdown viscosity but leave other flour pasting parameters generally unaltered. PINA transgenic lines were associated with increased small monomeric proteins, appearing to affect gluten aggregation. Our data together with several previous results highlight distinct effects of PINs on pasting properties depending on species and variety. The medium-hard kernel texture together with improved pasting parameters may be valuable for producing a broader range of end-products from durum wheat.

Co-expression of high-molecular-weight glutenin subunit 1Ax1 and Puroindoline a (Pina) genes in transgenic durum wheat (Triticum turgidum ssp. durum) improves milling and pasting quality

BACKGROUND

Durum wheat is considered not suitable for making many food products that bread wheat can. This limitation is largely due to: (i) lack of grain-hardness controlling genes (Puroindoline a and b) and consequently extremely-hard kernel; (ii) lack of high- and low-molecular-weight glutenin subunit loci (Glu-D1 and Glu-D3) that contribute to gluten strength. To improve food processing quality of durum wheat, we stacked transgenic Pina and HMW-glutenin subunit 1Ax1 in durum wheat and developed lines with medium-hard kernel texture.

RESULTS

Here, we demonstrated that co-expression of Pina + 1Ax1 in durum wheat did not affect the milling performance that was enhanced by Pina expression. While stacking of Pina + 1Ax1 led to increased flour yield, finer flour particles and decreased starch damage compared to the control lines. Interestingly, Pina and 1Ax1 co-expression showed synergistic effects on the pasting attribute peak viscosity. Moreover, Pina and 1Ax1 co-expression suggests that PINA impacts gluten aggregation via interaction with gluten protein matrix.

CONCLUSIONS

The results herein may fill the gap of grain hardness between extremely-hard durum wheat and the soft kernel durum wheat, the latter of which has been developed recently. Our results may also serve as a proof of concept that stacking Puroindolines and other genes contributing to wheat end-use quality from the A and/or D genomes could improve the above-mentioned bottleneck traits of durum wheat and help to expand its culinary uses.

Sequence Diversity and Identification of Novel Puroindoline and Grain Softness Protein Alleles in Elymus, Agropyron and Related Species

The puroindoline proteins, PINA and PINB, which are encoded by the Pina and Pinb genes located at the Ha locus on chromosome 5D of bread wheat, are considered to be the most important determinants of grain hardness. However, the recent identification of Pinb-2 genes on group 7 chromosomes has stressed the importance of considering the effects of related genes and proteins. Several species related to wheat (two diploid Agropyron spp., four tetraploid Elymus spp. and five hexaploid Elymus and Agropyron spp.) were therefore analyzed to identify novel variation in Pina, Pinb and Pinb-2 genes which could be exploited for the improvement of cultivated wheat. A novel sequence for the Pina gene was detected in Elymus burchan-buddae, Elymus dahuricus subsp. excelsus and Elymus nutans and novel PINB sequences in Elymus burchan-buddae, Elymus dahuricus subsp. excelsus, and Elymus nutans. A novel PINB-2 variant was also detected in Agropyron repens and Elymus repens. The encoded proteins detected all showed changes in the tryptophan-rich domain as well as changes in and/or deletions of basic and hydrophobic residues. In addition, two new AGP sequences were identified in Elymus nutans and Elymus wawawaiensis. The data presented therefore highlight the sequence diversity in this important gene family and the potential to exploit this diversity to modify grain texture and end-use quality in wheat.

Influence of Soft Kernel Texture on Fresh Durum Pasta

This study examined the quality of fresh pasta made from 3 varieties of a new type of durum wheat possessing soft kernel texture, as compared to fresh pasta made from commercial samples of durum semolina, durum flour, and bread flour, each at 3 levels of hydration (28%, 30%, and 32%, respectively). Soft durum possesses a small part of chromosome 5D that carries the Hardness locus and puroindoline genes. The soft durum lines were derived from the durum varieties Svevo, Alzada, and Havasu. The soft durum pasta exhibited low cooking weight increase (water uptake) (115% to 122%), the lowest cooking loss (∼3% to 4%), high firmness (269.3, 265.8, and 297.9 g, Soft Svevo, Soft Havasu, and Soft Alzada, respectively, versus 239.7 and 273.6 g, durum flour and semolina, respectively), low stickiness (4.17 to 4.96 g·s for the soft durums compared with 5.04 for the semolina), and raw and cooked pasta color comparable to or superior to those exhibited by the durum semolina (high L^* and b^* ). The soft durum samples also exhibited pasta quality superior to both the durum flour and bread flour samples. These results challenge the long-standing view that high-quality pasta must be made from durum semolina. PRACTICAL APPLICATION: This study illustrates the quality and potential applications of soft durum wheat in pasta manufacturing. As a new type of wheat, understanding these properties is crucial for manufacturers and others who may be interested in utilizing soft durum.

Molecular and Cytogenetic Characterization of the 5DS-5BS Chromosome Translocation Conditioning Soft Kernel Texture in Durum Wheat

The durum wheat ( ssp. (Desf.) Husn.) cultivar Soft Svevo with a soft kernel texture was developed through a -mediated homoeologous 5DS-5BS chromosomal translocation. The soft kernel trait ( locus) derived from chromosome 5D of the common wheat ( L.) cultivar Chinese Spring. Soft Svevo was used as the donor parent to create near-isogenic soft durum germplasm. The size of the translocation, its estimated breakpoint, and the amount of chromosome 5BS translocated, if any, remain unknown. Four near-isogenic pairs of hard and soft kernel durum genotypes, in addition to Soft Svevo and the Chinese Spring deletion line 5DS-2, which lacks a distal 22% terminal segment of chromosome 5DS, were genotyped using Illumina's 90k wheat single nucleotide polymorphism array. Single nucleotide polymorphism results were processed in GenomeStudio and 164 polymorphic markers were identified between the near-isogenic lines (NILs). Subsequent BLASTn results for two subsets of markers corresponding to the distal ends of chromosomes 5DS and 5BS indicated that the translocation event was nearly reciprocal, as a ∼24.36-Mbp segment of chromosome 5DS was gained, whereas a ∼20.01-Mbp segment of chromosome 5BS was lost. Genomic in situ hybridization images of the soft durum NILs agreed with these estimates and confirmed the absence of additional terminal or interstitial translocations. Soft durum represents the potential of a new wheat market class and these findings will assist durum wheat breeders in the development of new soft durum germplasm.