Molecular discrimination of Bx7 alleles demonstrates that a highly expressed high-molecular-weight glutenin allele has a major impact on wheat flour dough strength

High-molecular-weight glutenin subunits (HMW-GS) are important determinants of wheat dough quality as they confer visco-elastic properties to the dough required for mixing and baking performance. With this important role, the HMW-GS alleles are key markers in breeding programs. In this work, we present the use of a PCR marker initially designed to discriminate Glu1 Bx7 and Glu1 Bx17 HMW-GS. It was discovered that this marker also differentiated two alleles, originally both scored as Glu1 Bx7, present in the wheat lines CD87 and Katepwa respectively, by a size polymorphism of 18 bp. The marker was scored across a segregating doubled-haploid (DH) population (CD87 x Katepwa) containing 156 individual lines and grown at two sites. Within this population, the marker differentiated lines showing the over-expression of the Glu1 Bx7 subunit (indicated by the larger PCR fragment), derived from the CD87 parent, relative to lines showing the normal expression of the Glu1 Bx7 subunit, derived from the Katepwa parent. DNA sequence analysis showed that the observed size polymorphism was due to an 18 bp insertion/deletion event at the C-terminal end of the central repetitive domain of the Glu1 Bx 7 coding sequence, which resulted in an extra copy of the hexapeptide sequence QPGQGQ in the deduced amino-acid sequence of Bx7 from CD87. When the DH population was analysed using this novel Bx7 PCR marker, SDS PAGE and RP HPLC, there was perfect correlation between the Bx7 PCR marker results and the expression level of Bx7. This differentiation of the population was confirmed by both SDS-PAGE and RP-HPLC. The functional significance of this marker was assessed by measuring key dough properties of the 156 DH lines. A strong association was shown between lines with an over expression of Bx7 and high dough strength. Furthermore, the data demonstrated that there was an additional impact of Glu-D1 alleles on dough properties, with lines containing both over-expressed Bx7 and Glu-D1 5+10 having the highest levels of dough strength. However, there was no statistically significant epistatic interaction between Glu-B1 and Glu-D1 loci.

Bánkúti 1201--an old Hungarian wheat variety with special storage protein composition

Bánkúti 1201, an old Hungarian wheat variety with special quality traits, was analysed to determine the relationships between its storage protein composition and superior quality-attributes for breadmaking. Based on the storage protein composition, the variety appears to have the nature of a population, containing several genotypes with different gluten protein alleles. Using molecular markers, a new mutant x-type HMW glutenin allele was identified, containing an extra cysteine residue and showing a moderate, positive-effect on gluten properties. In lines possessing subunits Bx7+By8 the overexpression of the Bx-type subunit could be detected, resulting in a higher unextractable polymeric protein (UPP) content and increased dough strength. It was found that the presence or absence of subunit Bx7 has an equilibrating effect on the dough extensibility, which is generally characteristic of the Bánkúti 1201 population. The complex good bread-making quality of the variety, which has strong but highly extensible dough, is probably due to the balance between lines which express subunit Bx7 and those which do not.

Sequence and properties of HMW subunit 1Bx20 from pasta wheat (Triticum durum) which is associated with poor end use properties

The gene encoding high-molecular-weight (HMW) subunit 1Bx20 was isolated from durum wheat cv. Lira. It encodes a mature protein of 774 amino acid residues with an M(r) of 83,913. Comparison with the sequence of subunit 1Bx7 showed over 96% identity, the main difference being the substitution of two cysteine residues in the N-terminal domain of subunit 1Bx7 with tyrosine residues in 1Bx20. Comparison of the structures and stabilities of the two subunits purified from wheat using Fourier-transform infra-red and circular dichroism spectroscopy showed no significant differences. However, incorporation of subunit 1Bx7 into a base flour gave increased dough strength and stability measured by Mixograph analysis, while incorporation of subunit 1Bx20 resulted in small positive or negative effects on the parameters measured. It is concluded that the different effects of the two subunits could relate to the differences in their cysteine contents, thereby affecting the cross-linking and hence properties of the glutenin polymers.

Quality traits of wheat determined by small-scale dough testing methods

The dough properties of flours from the grain of 172 doubled haploid lines of a Cranbrook Halberd cross, grown at 3 locations, were determined with traditional and small-scale dough testing equipment. The experiments were aimed at determining the genetic factors that underpin the flour processing properties of wheat flour. Seven mixing parameters determined on a 2-g Mixograph™, as well as the maximum resistance (RMAX) and extensibility (EXT) measured on a Micro-Extension Tester, were identified as quality traits for genetic mapping studies, to identify the underlying quantitative trait loci (QTL). For each of the 3 locations in which the wheat lines were grown, relationships between the quality parameters and genetic markers were constructed for the populations. The associations of HMW- and LMW-glutenin allele combinations with the quality traits were investigated using ANOVA, linear parametric, and non-parametric methods. Of particular interest were qualitative and quantitative assessments of the extremes of the quality traits in each population. The relative contributions of the glutenincoding loci to quality were determined and it was found that the growing conditions to which wheat lines were subjected significantly affected the analyses. The nature and extent of these variations could not be explained by changes in protein content alone, and were related to environmentally induced alterations in the protein composition. From a comparison of the measurements made with the small-scale Mixograph™ with those from both the Extensograph™ and a Micro-Extension Tester, it was concluded that the same information about RMAX and EXT obtained from traditional extension testing could be obtained using small-scale dough tests. The data provided a direct validation for the application of small-scale testing for the screening of large populations. The comparisons of large and small scale testing procedures also provided the basis defining a new trait, ‘M-extensibility’, which is obtained from protein content and selected Mixograph data. This parameter was able to be measured more accurately and was shown to be closely related to the traditional extensibility measurement, and thus very useful for molecular/genetic analysis. The M-extensibility trait could be mapped as a major QTL to LMW-glutenin subunit loci on chromosomes 1B and 1D.

Gluten protein functionality in wheat flour processing: a review

Gluten protein functionality remains the basis of any understanding of the end-product quality of wheat flours. Information about this functionality has been obtained by both in vivo and in vitro studies. Recent advances include structure/function studies of deletion mutants and transformed genotypes, where the genes incorporated were both naturally occurring genes and genes which have been desired to provide specific structural features. The contributions of these specific changes in structure to the rheology of the resulting doughs allow insight into the underlying physical processes that determine dough and end-product properties.

Flour proteins linked to quality traits in an Australian doubled haploid wheat population

The Cranbrook/Halberd doubled haploid population has provided a unique opportunity to examine in detail the contributions made by a number of different high molecular weight (HMW) and low molecular weight (LMW) glutenin alleles to the dough properties in a set of homogeneous lines of wheat. A range of different instruments was employed, including Farinograph, Extensograph, Do-Corder, Resistograph, and GRL/EasyMix, to study the dough rheology of the lines from 3 sites over 2 years. Correlation studies showed that 2 basic parameters (dough strength and extensibility) were measured by these different instruments. The results presented are mainly from the Extensograph, which is a major Australian standard for determining release and marketing classification of Australian wheats. Approaches to investigate the data include bulk segregant analysis, distribution of protein alleles in the population, and multiple linear regression. As expected, the HMW glutenin alleles made a major contribution to dough strength, with a minor, but not insignificant, contribution from the LMW glutenin alleles. From a knowledge of their glutenin alleles, a glutenin strength score (GSS) was devised to allow breeders to rank the dough strength of various lines. The GSS scoring system is based on both HMW and LMW glutenin alleles, adding to a total out of 10. Extensibility, on the other hand, was predominantly influenced by protein levels in the flour and environmental conditions such as site and season. However, the LMW glutenin alleles make a significant genetic contribution to the extensibility, which can be assessed by using a glutenin extensibility score. These two glutenin quality scores currently include only the alleles present in the parents, Cranbrook and Halberd, but this could be expanded to include a wider range of alleles by analysis of the quality data from other doubled haploid populations. These quality scores would then be an extremely useful tool for assessing the potential quality of parental and early generation germplasm in wheat breeding programs, by a knowledge of the allelic composition of their HMW and LMW glutenins.

Targetting AFLP-DNA markers to specific traits and chromosome regions

The amplified fragment length polymorphism (AFLP) technique is widely used in mapping of wheat as high polymorphism rates are obtained and the procedure is relatively simple. In this study the AFLP markers were targetted to wheat chromosome regions of interest, especially those in which random mapping approaches located relatively few markers. Results showed that the combination of bulk segregant analysis and AFLP markers could target new markers to regions of interest in wheat, and as a result, additional markers were identified for the dough mixing time and noodle colour traits. The new markers for noodle colour were closer to this trait than the markers previously identified by random procedures. As a result, their association with the trait was more significant, an aspect that is important for selection efficiency. In order to improve genome coverage, it was found that regions of chromosomes containing telomere sequences could be targetted using AFLPs combined with a telomere sequence anchor primer.

Grain proteins as markers of genetic traits in wheat

Different protein fractionation techniques were used to define differences between a set of 8 wheat lines used in genetic mapping studies in Australia. A proteomics approach was used to establish the feasibility of identifying new protein polymorphisms for mapping purposes. Detailed analysis confirmed differences in the glutenin subunits, gliadin proteins, and 10–20 other proteins, between the mapping population parents, Cranbrook, Halberd, CD87, and Katepwa. Differences were particularly evident in the low molecular weight classes of protein. Alternative technologies were used to determine the differences in various protein classes in order to screen doubled haploid lines derived from crosses between the wheat lines. Polyacrylamide gel electrophoresis analysis allowed the mapping of loci encoding high molecular weight (HMW) and low molecular weight (LMW) glutenin subunit proteins. Reversed phase high performance liquid chromatography also allowed several loci encoding LMW glutenin subunit proteins to be mapped, as well as a new protein on chromosome 6A. Capillary electrophoresis provided a high-resolution system that was used to map several gliadin-type proteins. The studies showed that proteins provide useful genetic markers and the data are discussed from the point of view of the advantages that protein-based markers offer in providing both genotypic and phenotypic data.

Transformation of wheat with high molecular weight subunit genes results in improved functional properties

The high molecular weight (HMW) subunits of wheat glutenin are major determinants of the elastic properties of gluten that allow the use of wheat doughs to make bread, pasta, and a range of other foods. There are both quantitative and qualitative effects of HMW subunits on the quality of the grain, the former being related to differences in the number of expressed HMW subunit genes. We have transformed bread wheat in order to increase the proportions of the HMW subunits and improve the functional properties of the flour. A range of transgene expression levels was obtained with some of the novel subunits present at considerably higher levels than the endogenous subunits. Analysis of T2 seeds expressing transgenes for one or two additional HMW subunits showed stepwise increases in dough elasticity, demonstrating the improvement of the functional properties of wheat by genetic engineering.

[Determination of vitamin D3 in premixes and mixed feeds]

The authors developed a two-dimensional thin-layer chromatographic method for the qualitative and quantitative determination of vitamin D3 in premixes and mixed feeds. The procedure permits to determine I.U. = 0.128 micrograms of vitamin D3. The method is illustrated by the description of the analyses of 3 premixes and 5 mixed feeds.

[Some new results from isolation and fractionation of low molecular weight wheat proteins]

The alcohol-soluble wheat gluten fraction (gliadine) and the petroleum-ether-soluble wheat protein fraction (purothionine) were isolated and analysed. The gliadine fraction was itself fractionated by gel chromatography (Sephadex G-100). The partial hydrolysis of sub-fractions (molecular weight 20000-30000) yielded (after separation by gel and ion-exchange chromatography) several peptide fractions. The amino-acid composition and the N- and C-terminal groups of the gliadine fractions were determined. Characteristic differences were stated between various fractions. By means of gel chromatography, purothionine was separated into 4-6 fractions. The study of the amino-acid composition and of the N-terminal groups of the fractions revealed differences in both properties.