Effects of two novel Wx-A1 alleles of common wheat (Triticum aestivum L.) on amylose and starch properties

An Overview of Factors Affecting the Functional Quality of Common Wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) is one of the most important crops worldwide, and, as a resilient cereal, it grows in various climatic zones. Due to changing climatic conditions and naturally occurring environmental fluctuations, the priority problem in the cultivation of wheat is to improve the quality of the crop. Biotic and abiotic stressors are known factors leading to the deterioration of wheat grain quality and to crop yield reduction. The current state of knowledge on wheat genetics shows significant progress in the analysis of gluten, starch, and lipid genes responsible for the synthesis of the main nutrients in the endosperm of common wheat grain. By identifying these genes through transcriptomics, proteomics, and metabolomics studies, we influence the creation of high-quality wheat. In this review, previous works were assessed to investigate the significance of genes, puroindolines, starches, lipids, and the impact of environmental factors, as well as their effects on the wheat grain quality.

A single base change at exon of Wx-A1 caused gene inactivation and starch properties modified in a wheat EMS mutant line

BACKGROUND

Wheat is an essential source of starch. The GBSS or waxy genes are responsible for synthesizing amylose in cereals. The present study identified a novel Wx-A1 null mutant line from an ethyl methanesulfonate (EMS)-mutagenized population of common wheat cv. SM126 using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and agarose gel analyses.

RESULTS

The alignment of the Wx-A1 gene sequences from the mutant and parental SM126 lines showed only one single nucleotide polymorphism causing the appearance of a premature stop codon and Wx-A1 inactivation. The lack of Wx-A1 protein resulted in decreased amylose, total starch and resistant starch. The starch morphology assessment revealed that starch from mutant seeds was more wrinkled, increasing its susceptibility to digestion. Regarding the starch thermodynamic properties, the gelatinization temperature was remarkably reduced in the mutant compared to parental line SM126. The digestibility of native, gelatinized, and retrograded starches was analyzed for mutant M4-627 and the parental SM126 line. In the M4-627 line, rapidly digestible starch contents were increased, whereas resistant starch was decreased in the three types of starch.

CONCLUSION

Waxy protein is essential for starch synthesis. The thermodynamic characteristics were decreased in the Wx-A1 mutant line. The digestibility properties of starch were also affected. Therefore, the partial waxy mutant M3-627 might play a significant role in food improvement. Furthermore, it might also be used to produce high-quality noodles. © 2021 Society of Chemical Industry.

Identification and molecular characterization of mutant line deficiency in three waxy proteins of common wheat (Triticum aestivum L.)

Starch is the main component of wheat (Triticum aestivum L.) grain and a key factor in determining wheat processing quality. The Wx gene is the gene responsible for amylose synthesis. An ethyl methanesulfonate (EMS) mutagenized population was generated using common wheat cv. Gao 8901, a popular and high-quality cultivar in China. A waxy mutant (Wx-null) was isolated by screening M3 seeds with KI-I₂ staining of endosperm starch. No obvious waxy proteins in Wx-null line were detected using Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). DNA sequencing revealed three SNPs and a 3-bp InDel in the first exon, and a 16-bp InDel at the junction region of the first Wx-A1 intron from the Wx-null line. Six SNPs were identified in Wx-B1 gene of Wx-null line compared to the wild-type Gao 8901, including four missense mutations. One nonsense mutation was found at position 857 in the fourth exon, which resulted in a premature stop codon. Expression levels of Wx genes were dramatically reduced in the Wx-null line. There were no detectable differences in granule size and morphology between Wx-null and wild-type, but the Wx-null line contained more B-type starch granules. The amylose content of the Wx-null line (0.22%) was remarkably lower compared to the wild-type Gao 8901 (24.71%). Total starch is also lower in the Wx-null line. The Wx-null line may provide a potential waxy material with high agronomic performance in wheat breeding programs.

DAWN: a resource for yielding insights into the diversity among wheat genomes

BACKGROUND

Democratising the growing body of whole genome sequencing data available for Triticum aestivum (bread wheat) has been impeded by the lack of a genome reference and the large computational requirements for analysing these data sets.

RESULTS

DAWN (Diversity Among Wheat geNomes) integrates data from the T. aestivum Chinese Spring (CS) IWGSC RefSeq v1.0 genome with public WGS and exome data from 17 and 62 accessions respectively, enabling researchers and breeders alike to investigate genotypic differences between wheat accessions at the level of whole chromosomes down to individual genes.

CONCLUSIONS

Using DAWN we show that it is possible to visualise small and large chromosomal deletions, identify haplotypes at a glance and spot the consequences of selective breeding. DAWN allows us to detect the break points of alien introgression segments brought into an accession when transferring desired genes. Furthermore, we can find possible explanations for reduced recombination in parts of a chromosome, we can predict regions with linkage drag, and also look at diversity in centromeric regions.

Wheat waxy proteins: polymorphism, molecular characterization and effects on starch properties

The starch fraction, comprising about 70% of the total dry matter in the wheat grain, can greatly affect the end-use quality of products made from wheat kernels, especially Asian noodles. Starch is associated with the shelf life and nutritional value (glycaemic index) of different wheat products. Starch quality is closely associated with the ratio of amylose to amylopectin, the two main macromolecules forming starch. In this review, we briefly summarise the discovery of waxy proteins-shown to be the sole enzymes responsible for amylose synthesis in wheat. The review particularly focuses on the different variants of these proteins, together with their molecular characterisation and evaluation of their effects on starch composition. There have been 19 different waxy protein variants described using protein electrophoresis; and at a molecular level 19, 15 and seven alleles described for Wx-A1, Wx-B1 and Wx-D1, respectively. This large variability, found in modern wheat and genetic resources such as wheat ancestors and wild relatives, is in some cases not properly ordered. The proper ordering of all the data generated is the key to enhancing use in breeding programmes of the current variability described, and thus generating wheat with novel starch properties to satisfy the demand of industry and consumers for novel high-quality processed food.

Molecular characterization of waxy alleles in three subspecies of hexaploid wheat and identification of two novel Wx-B1 alleles

Two novel Wx - B1 null alleles that enlarge the genetic variability for this wheat gene were characterized, whose effects on wheat quality could be different to those of the Wx - B1b allele. The starch composition of wheat grain has a primary influence on flour quality. Wheat starch consists of two types of glucose polymers: amylose (22-35% of the total) and amylopectin (68-75% of the total). Amylose is synthesized by waxy proteins. Several studies have contributed to the catalogue of waxy alleles available for breeders, and the search for novel alleles of these and other proteins related to flour quality continues. In this report, we describe the characterization of two novel Wx-B1 alleles (Wx-B1k and Wx-B1m) in a collection of macha, Indian dwarf and club wheat. Several accessions lacking Wx-B1 protein were detected, and some were caused by the common Wx-B1b null allele. Of the other accessions, four from Indian dwarf wheat showed the insertion of 4 bp within the seventh exon, and one from club wheat had a deletion of four nucleotides in the second exon. These mutations were novel and provisionally catalogued as Wx-B1k and Wx-B1m, respectively, and could be used to enlarge the genetic variability for this gene.

Molecular characterization of a new waxy allele with partial expression in spelt wheat

Starch composition which is dependent on the waxy protein, the enzyme responsible for amylose synthesis in the grain, is an important aspect of the wheat quality. In this report, we describe the characterization of a novel Wx-A1 allele (Wx-A1g formerly known as -Wx-A1a) in Spanish spelt wheat lines which is responsible for a remarkable decline in the concentration of Wx-A1 protein found in the endosperm. Comparison of the DNA sequences in the Wx-A1a and Wx-A1g alleles showed the presence of a 160-bp insertion within the fourth intron in the latter. This insertion had some characteristics of a transposable-like element. RT-PCR analysis showed the presence of normal and aberrant mRNA transcripts in the Wx-A1g lines, indicating that the aberrant transcripts are un-spliced and contained the longer fourth intron. This may be related to the low level of Wx-A1 protein in these lines. In addition, a simple and fast PCR assay was designed for differentiating among different Wx-A1 alleles (a, b, f and g). The mutation described here is not related to either of the Wx-A1 mutations identified previously in common and durum wheats and could help to extend the range of amylose content of wheats.