Linkage relationships between prolamin genes on chromosomes 1A and 1B of durum wheat

Enhancing Wheat Flour Quality Through Introgression of High-Molecular-Weight Glutenin Subunits From Aegilops tauschii Accessions

Narrow genetic diversity in the wheat gene pool restricts the improvement of wheat quality traits. Aegilops tauschii possesses valuable genetic diversity that can be used to improve not only biotic and abiotic stresses in arid regions but also wheat yield and quality. Our study, which used 392 multiple synthetic derivatives (MSD) panel developed with Ae. tauschii Coss. introgressions, had three main aims: to explore the genetic diversity of high-molecular-weight glutenin subunits (HMW-GS), to investigate the dough strength and the relationship between protein content and grain yield, and to identify lines with a good flour quality. A wide range of allelic diversity was observed at the Glu-D1 locus, reflecting the impact of the different introgressed portions of Ae. tauschii, and a wide variation was found in dough strength even between lines having the same composition of HMW-GS. We report a negative impact on dough strength of subunit 5t+10t from Ae. tauschii and a relatively positive impact of subunit 2t+12.1t. We identified four MSD lines with significantly enhanced flour quality. Regressing the grain yield of the MSD lines against protein content showed no correlation between the two traits and identified lines with comparable grain yield to the recurrent parent and higher protein content. The identified MSD lines could provide a valuable genetic resource for enhancing the end-use quality of flour without any loss in productivity.

Proteomic Determination of Low-Molecular-Weight Glutenin Subunit Composition in Aroona Near-Isogenic Lines and Standard Wheat Cultivars

The low-molecular weight glutenin subunit (LMW-GS) composition of wheat (Triticum aestivum) flour has important effects on end-use quality. However, assessing the contributions of each LMW-GS to flour quality remains challenging because of the complex LMW-GS composition and allelic variation among wheat cultivars. Therefore, accurate and reliable determination of LMW-GS alleles in germplasm remains an important challenge for wheat breeding. In this study, we used an optimized reversed-phase HPLC method and proteomics approach comprising 2-D gels coupled with liquid chromatography–tandem mass spectrometry (MS/MS) to discriminate individual LMW-GSs corresponding to alleles encoded by the Glu-A3, Glu-B3, and Glu-D3 loci in the ‘Aroona’ cultivar and 12 ‘Aroona’ near-isogenic lines (ARILs), which contain unique LMW-GS alleles in the same genetic background. The LMW-GS separation patterns for ‘Aroona’ and ARILs on chromatograms and 2-D gels were consistent with those from a set of 10 standard wheat cultivars for Glu-3. Furthermore, 12 previously uncharacterized spots in ‘Aroona’ and ARILs were excised from 2-D gels, digested with chymotrypsin, and subjected to MS/MS. We identified their gene haplotypes and created a 2-D gel map of LMW-GS alleles in the germplasm for breeding and screening for desirable LMW-GS alleles for wheat quality improvement.

New Findings in the Amino Acid Profile and Gene Expression in Contrasting Durum Wheat Gluten Strength Genotypes during Grain Filling

Grain protein composition is important in wheat quality and may influence the amino acidic sequence of bioactive peptides obtained from this feedstock. However, the genetic basis modulating the amino acid profile in durum wheat is not well-understood. Therefore, strong and weak gluten strength durum wheat genotypes were evaluated for their amino acid composition along grain filling. Strong gluten strength lines showed higher expression levels of low-molecular-weight glutenin-related genes between 21 and 35 days post-anthesis (DPA) and exhibited up to 43.5% more alanine than the weak lines at 42 DPA, which was supported by the higher expression levels of putative alanine amino transferase genes in strong genotypes. Therefore, with the involvement of chemistry and molecular biology, the results present here may influence the science of wheat.

Genetic dissection of agronomic and quality traits based on association mapping and genomic selection approaches in durum wheat grown in Southern Spain

Climatic conditions affect the growth, development and final crop production. As wheat is of paramount importance as a staple crop in the human diet, there is a growing need to study its abiotic stress adaptation through the performance of key breeding traits. New and complementary approaches, such as genome-wide association studies (GWAS) and genomic selection (GS), are used for the dissection of different agronomic traits. The present study focused on the dissection of agronomic and quality traits of interest (initial agronomic score, yield, gluten index, sedimentation index, specific weight, whole grain protein and yellow colour) assessed in a panel of 179 durum wheat lines (Triticum durum Desf.), grown under rainfed conditions in different Mediterranean environments in Southern Spain (Andalusia). The findings show a total of 37 marker-trait associations (MTAs) which affect phenotype expression for three quality traits (specific weight, gluten and sedimentation indexes). MTAs could be mapped on the A and B durum wheat subgenomes (on chromosomes 1A, 1B, 2A, 2B and 3A) through the recently available bread wheat reference assembly (IWGSC RefSeqv1). Two of the MTAs found for quality traits (gluten index and SDS) corresponded to the known Glu-B1 and Glu-A1 loci, for which candidate genes corresponding to high molecular weight glutenin subunits could be located. The GS prediction ability values obtained from the breeding materials analyzed showed promising results for traits as grain protein content, sedimentation and gluten indexes, which can be used in plant breeding programs.

Towards reducing the immunogenic potential of wheat flour: omega gliadins encoded by the D genome of hexaploid wheat may also harbor epitopes for the serious food allergy WDEIA

BACKGROUND

Omega-5 gliadins are a group of highly repetitive gluten proteins in wheat flour encoded on the 1B chromosome of hexaploid wheat. These proteins are the major sensitizing allergens in a severe form of food allergy called wheat-dependent exercise-induced anaphylaxis (WDEIA). The elimination of omega-5 gliadins from wheat flour through biotechnology or breeding approaches could reduce the immunogenic potential and adverse health effects of the flour.

RESULTS

A mutant line missing low-molecular weight glutenin subunits encoded at the Glu-B3 locus was selected previously from a doubled haploid population generated from two Korean wheat cultivars. Analysis of flour from the mutant line by 2-dimensional gel electrophoresis coupled with tandem mass spectrometry revealed that the omega-5 gliadins and several gamma gliadins encoded by the closely linked Gli-B1 locus were also missing as a result of a deletion of at least 5.8 Mb of chromosome 1B. Two-dimensional immunoblot analysis of flour proteins using sera from WDEIA patients showed reduced IgE reactivity in the mutant relative to the parental lines due to the absence of the major omega-5 gliadins. However, two minor proteins showed strong reactivity to patient sera in both the parental and the mutant lines and also reacted with a monoclonal antibody against omega-5 gliadin. Analysis of the two minor reactive proteins by mass spectrometry revealed that both proteins correspond to omega-5 gliadin genes encoded on chromosome 1D that were thought previously to be pseudogenes.

CONCLUSIONS

While breeding approaches can be used to reduce the levels of the highly immunogenic omega-5 gliadins in wheat flour, these approaches are complicated by the genetic linkage of different classes of gluten protein genes and the finding that omega-5 gliadins may be encoded on more than one chromosome. The work illustrates the importance of detailed knowledge about the genomic regions harboring the major gluten protein genes in individual wheat cultivars for future efforts aimed at reducing the immunogenic potential of wheat flour.

Evidence of intralocus recombination at the Glu-3 loci in bread wheat (Triticum aestivum L.)

Recombination at the Glu-3 loci was identified, and strong genetic linkage was observed only between the amplicons representing i-type and s-type genes located, respectively, at the Glu-A3 and Glu-B3 loci. The low-molecular weight glutenin subunits (LMW-GSs) are one of the major components of wheat seed storage proteins and play a critical role in the determination of wheat end-use quality. The genes encoding this class of proteins are located at the orthologous Glu-3 loci (Glu-A3, Glu-B3, and Glu-D3). Due to the complexity of these chromosomal regions and the high sequence similarity between different LMW-GS genes, their organization and recombination characteristics are still incompletely understood. This study examined intralocus recombination at the Glu-3 loci in two recombinant inbred line (RIL) and one doubled haploid (DH) population, all segregating for the Glu-A3, Glu-B3, and Glu-D3 loci. The analysis was conducted using a gene marker system that consists of the amplification of the complete set of the LMW-GS genes and their visualization by capillary electrophoresis. Recombinant marker haplotypes were detected in all three populations with different recombination rates depending on the locus and the population. No recombination was observed between the amplicons representing i-type and s-type LMW-GS genes located, respectively, at the Glu-A3 and Glu-B3 loci, indicating tight linkage between these genes. Results of this study contribute to better understanding the genetic linkage and recombination between different LMW-GS genes, the structure of the Glu-3 loci, and the development of more specific molecular markers that better represent the genetic diversity of these loci. In this way, a more precise analysis of the contribution of various LMW-GSs to end-use quality of wheat may be achieved.

Genetic Diversity and Association Mapping for Agromorphological and Grain Quality Traits of a Structured Collection of Durum Wheat Landraces Including subsp. durum, turgidum and diccocon

Association mapping was performed for 18 agromorphological and grain quality traits in a set of 183 Spanish landraces, including subspecies durum, turgidum and dicoccon, genotyped with 749 DArT (Diversity Array Technology) markers. Large genetic and phenotypic variability was detected, being the level of diversity among the chromosomes and genomes heterogeneous, and sometimes complementary, among subspecies. Overall, 356 were monomorphic in at least one subspecies, mainly in dicoccon, and some of them coincidental between subspecies, especially between turgidum and dicoccon. Several of those fixed markers were associated to plant responses to environmental stresses or linked to genes subjected to selection during tetraploid wheat domestication process. A total of 85 stable MTAs (marker–trait associations) have been identified for the agromorphological and quality parameters, some of them common among subspecies and others subspecies-specific. For all the traits, we have found MTAs explaining more than 10% of the phenotypic variation in any of the three subspecies. The number of MTAs on the B genome exceeded that on the A genome in subsp. durum, equalled in turgidum and was below in dicoccon. The validation of several adaptive and quality trait MTAs by combining the association mapping with an analysis of the signature of selection, identifying the putative gene function of the marker, or by coincidences with previous reports, showed that our approach was successful for the detection of MTAs and the high potential of the collection to identify marker–trait associations. Novel MTAs not previously reported, some of them subspecies specific, have been described and provide new information about the genetic control of complex traits.

Composition and functional analysis of low-molecular-weight glutenin alleles with Aroona near-isogenic lines of bread wheat

BACKGROUND

Low-molecular-weight glutenin subunits (LMW-GS) strongly influence the bread-making quality of bread wheat. These proteins are encoded by a multi-gene family located at the Glu-A3, Glu-B3 and Glu-D3 loci on the short arms of homoeologous group 1 chromosomes, and show high allelic variation. To characterize the genetic and protein compositions of LMW-GS alleles, we investigated 16 Aroona near-isogenic lines (NILs) using SDS-PAGE, 2D-PAGE and the LMW-GS gene marker system. Moreover, the composition of glutenin macro-polymers, dough properties and pan bread quality parameters were determined for functional analysis of LMW-GS alleles in the NILs.

RESULTS

Using the LMW-GS gene marker system, 14-20 LMW-GS genes were identified in individual NILs. At the Glu-A3 locus, two m-type and 2-4 i-type genes were identified and their allelic variants showed high polymorphisms in length and nucleotide sequences. The Glu-A3d allele possessed three active genes, the highest number among Glu-A3 alleles. At the Glu-B3 locus, 2-3 m-type and 1-3 s-type genes were identified from individual NILs. Based on the different compositions of s-type genes, Glu-B3 alleles were divided into two groups, one containing Glu-B3a, B3b, B3f and B3g, and the other comprising Glu-B3c, B3d, B3h and B3i. Eight conserved genes were identified among Glu-D3 alleles, except for Glu-D3f. The protein products of the unique active genes in each NIL were detected using protein electrophoresis. Among Glu-3 alleles, the Glu-A3e genotype without i-type LMW-GS performed worst in almost all quality properties. Glu-B3b, B3g and B3i showed better quality parameters than the other Glu-B3 alleles, whereas the Glu-B3c allele containing s-type genes with low expression levels had an inferior effect on bread-making quality. Due to the conserved genes at Glu-D3 locus, Glu-D3 alleles showed no significant differences in effects on all quality parameters.

CONCLUSIONS

This work provided new insights into the composition and function of 18 LMW-GS alleles in bread wheat. The variation of i-type genes mainly contributed to the high diversity of Glu-A3 alleles, and the differences among Glu-B3 alleles were mainly derived from the high polymorphism of s-type genes. Among LMW-GS alleles, Glu-A3e and Glu-B3c represented inferior alleles for bread-making quality, whereas Glu-A3d, Glu-B3b, Glu-B3g and Glu-B3i were correlated with superior bread-making quality. Glu-D3 alleles played minor roles in determining quality variation in bread wheat. Thus, LMW-GS alleles not only affect dough extensibility but greatly contribute to the dough resistance, glutenin macro-polymers and bread quality.

Catalogue of alleles of gliadin-coding loci in durum wheat (Triticum durum Desf.)

Gliadins are seed storage proteins which are characterized by high intervarietal polymorphism and can be used as genetic markers. As a result of our work, a considerably extended catalogue of allelic variants of gliadin component blocks was compiled for durum wheat; 74 allelic variants for four gliadin-coding loci were identified for the first time. The extended catalogue includes a total of 131 allelic variants: 16 for locus Gli-A1(d), 19 for locus Gli-B1(d), 41 for locus Gli-A2(d), and 55 for locus Gli-B2(d). The electrophoretic pattern of the standard cultivar and a diagram are provided for every block identified. The number of alleles per family is quite small for loci Gli-A1(d) and Gli-B1(d) of durum wheat, as contrasted to loci Gli-A2(d) and Gli-B2(d) that are characterized by large families including many alleles. The presence of large block families determines a higher diversity of durum wheat for loci Gli-A2(d) and Gli-B2(d) as compared to Gli-A1(d) and Gli-B1(d). The catalogue of allelic variants of gliadin component blocks can be used by seed farmers to identify durum wheat cultivars and evaluate their purity; by breeders, to obtain homogenous cultivars and control the initial stages of selection; by gene bank experts, to preserve native varieties and the original biotypic composition of cultivars.

New insights into the organization, recombination, expression and functional mechanism of low molecular weight glutenin subunit genes in bread wheat

The bread-making quality of wheat is strongly influenced by multiple low molecular weight glutenin subunit (LMW-GS) proteins expressed in the seeds. However, the organization, recombination and expression of LMW-GS genes and their functional mechanism in bread-making are not well understood. Here we report a systematic molecular analysis of LMW-GS genes located at the orthologous Glu-3 loci (Glu-A3, B3 and D3) of bread wheat using complementary approaches (genome wide characterization of gene members, expression profiling, proteomic analysis). Fourteen unique LMW-GS genes were identified for Xiaoyan 54 (with superior bread-making quality). Molecular mapping and recombination analyses revealed that the three Glu-3 loci of Xiaoyan 54 harbored dissimilar numbers of LMW-GS genes and covered different genetic distances. The number of expressed LMW-GS in the seeds was higher in Xiaoyan 54 than in Jing 411 (with relatively poor bread-making quality). This correlated with the finding of higher numbers of active LMW-GS genes at the A3 and D3 loci in Xiaoyan 54. Association analysis using recombinant inbred lines suggested that positive interactions, conferred by genetic combinations of the Glu-3 locus alleles with more numerous active LMW-GS genes, were generally important for the recombinant progenies to attain high Zeleny sedimentation value (ZSV), an important indicator of bread-making quality. A higher number of active LMW-GS genes tended to lead to a more elevated ZSV, although this tendency was influenced by genetic background. This work provides substantial new insights into the genomic organization and expression of LMW-GS genes, and molecular genetic evidence suggesting that these genes contribute quantitatively to bread-making quality in hexaploid wheat. Our analysis also indicates that selection for high numbers of active LMW-GS genes can be used for improvement of bread-making quality in wheat breeding.

Molecular characterization of novel low-molecular-weight glutenin genes in Aegilops longissima

Extensive genetic variations of low-molecular-weight glutenin subunits (LMW-GS) and their coding genes were found in the wild diploid A- and D-genome donors of common wheat. In this study, we reported the isolation and characterization of 8 novel LMW-GS genes from Ae.longissima Schweinf. & Muschl., a species of the section Sitopsis of the genus Aegilops, which is closely related to the B genome of common wheat. Based on the N-terminal domain sequences, the 8 genes were divided into 3 groups. A consensus alignment of the extremely conserved domains with known gene groups and the subsequent cluster analysis showed that 2 out of the 3 groups of LMW-GS genes were closely related to those from the B genome, and the remaining was related to those from A and D genomes of wheat and Ae. tauschii. Using 3 sets of gene-group-specific primers, PCRs in diploid, tetraploid and hexaploid wheats and Ae. tauschii failed to obtain the expected products, indicating that the 3 groups of LMW-GS genes obtained in this study were new members of LMW-GS multi-gene families. These results suggested that the Sitopsis species of the genus Aegilops with novel gene variations could be used as valuable gene resources of LMW-GS. The 3 sets of group-specific primers could be utilized as molecular markers to investigate the introgression of novel alien LMW-GS genes from Ae. longissima into wheat.

Removing celiac disease-related gluten proteins from bread wheat while retaining technological properties: a study with Chinese Spring deletion lines

BACKGROUND

Gluten proteins can induce celiac disease (CD) in genetically susceptible individuals. In CD patients gluten-derived peptides are presented to the immune system, which leads to a CD4+ T-cell mediated immune response and inflammation of the small intestine. However, not all gluten proteins contain T-cell stimulatory epitopes. Gluten proteins are encoded by multigene loci present on chromosomes 1 and 6 of the three different genomes of hexaploid bread wheat (Triticum aestivum) (AABBDD).

RESULTS

The effects of deleting individual gluten loci on both the level of T-cell stimulatory epitopes in the gluten proteome and the technological properties of the flour were analyzed using a set of deletion lines of Triticum aestivum cv. Chinese Spring. The reduction of T-cell stimulatory epitopes was analyzed using monoclonal antibodies that recognize T-cell epitopes present in gluten proteins. The deletion lines were technologically tested with respect to dough mixing properties and dough rheology. The results show that removing the alpha-gliadin locus from the short arm of chromosome 6 of the D-genome (6DS) resulted in a significant decrease in the presence of T-cell stimulatory epitopes but also in a significant loss of technological properties. However, removing the omega-gliadin, gamma-gliadin, and LMW-GS loci from the short arm of chromosome 1 of the D-genome (1DS) removed T-cell stimulatory epitopes from the proteome while maintaining technological properties.

CONCLUSION

The consequences of these data are discussed with regard to reducing the load of T-cell stimulatory epitopes in wheat, and to contributing to the design of CD-safe wheat varieties.

A catalogue of Triticum monococcum genes encoding toxic and immunogenic peptides for celiac disease patients

The celiac disease (CD) is an inflammatory condition characterized by injury to the lining of the small-intestine on exposure to the gluten of wheat, barley and rye. The involvement of gluten in the CD syndrome has been studied in detail in bread wheat, where a set of “toxic” and “immunogenic” peptides has been defined. For wheat diploid species, information on CD epitopes is poor. In the present paper, we have adopted a genomic approach in order to understand the potential CD danger represented by storage proteins in diploid wheat and sequenced a sufficiently large number of cDNA clones related to storage protein genes of Triticum monococcum. Four bona fide toxic peptides and 13 immunogenic peptides were found. All the classes of storage proteins were shown to contain harmful sequences. The major conclusion is that einkorn has the full potential to induce the CD syndrome, as already evident for polyploid wheats. In addition, a complete overview of the storage protein gene arsenal in T. monococcum is provided, including a full-length HMW x-type sequence and two partial HMW y-type sequences.

Novel DNA variations to characterize low molecular weight glutenin Glu-D3 genes and develop STS markers in common wheat

Low-molecular-weight glutenin subunits (LMW-GS) play an important role in bread and noodle processing quality by influencing the viscoelasticity and extensibility of dough. The objectives of this study were to characterize Glu-D3 subunit coding genes and to develop molecular markers for identifying Glu-D3 gene haplotypes. Gene specific primer sets were designed to amplify eight wheat cultivars containing Glu-D3a, b, c, d and e alleles, defined traditionally by protein electrophoretic mobility. Three novel Glu-D3 DNA sequences, designated as GluD3-4, GluD3-5 and GluD3-6, were amplified from the eight wheat cultivars. GluD3-4 showed three allelic variants or haplotypes at the DNA level in the eight cultivars, which were designated as GluD3-41, GluD3-42 and GluD3-43. Compared with GluD3-42, a single nucleotide polymorphism (SNP) was detected for GluD3-43 in the coding region, resulting in a pseudo-gene with a nonsense mutation at the 119th position of deduced peptide, and a 3-bp insertion was found in the coding region of GluD3-41, leading to a glutamine insertion at the 249th position of its deduced protein. The coding regions for GluD3-5 and GluD3-6 showed no allelic variation in the eight cultivars tested, indicating that they were relatively conservative in common wheat. Based on the 12 allelic variants of three Glu-D3 genes identified in this study and three detected previously, seven STS markers were established to amplify the corresponding gene sequences in wheat cultivars containing five Glu-D3 alleles (a, b, c, d and e). The seven primer sets M2F12/M2R12, M2F2/M2R2, M2F3/M2R3, M3F1/M3R1, M3F2/M3R2, M4F1/M4R1 and M4F3/M4R3 were specific to the allelic variants GluD3-21/22, GluD3-22, GluD3-23, GluD3-31, GluD3-32, GluD3-41 and GluD3-43, respectively, which were validated by amplifying 20 Chinese wheat cultivars containing alleles a, b, c and f based on protein electrophoretic mobility. These markers will be useful to identify the Glu-D3 gene haplotypes in wheat breeding programs.

Analysis and validation of genome-specific DNA variations in 5' flanking conserved sequences of wheat low-molecular-weight glutenin subunit gene

The thirty-three 5' flanking conserved sequences of the known low-molecular-weight subunit (LMW-GS) genes have been divided into eight clusters, which was in agreement with the classification based on the deduced N-terminal protein sequences. The DNA polymorphism between the eight clusters was obtained by sequence alignment, and a total of 34 polymorphic positions were observed in the approximately 200 bp regions, among which 18 polymorphic positions were candidate SNPs. Seven cluster-specific primer sets were designed for seven out of eight clusters containing cluster-specific bases, with which the genomic DNA of the ditelosomic lines of group 1 chromosomes of a wheat variety 'Chinese Spring' was employed to carry out chromosome assignment. The subsequent cloning and DNA sequencing of PCR fragments validated the sequences specificity of the 5' flanking conserved sequences between LMW-GS gene groups in different genomes. These results suggested that the coding and 5' flanking regions of LMW-GS genes are likely to have evolved in concerted fashion. The seven primer sets developed in this study could be used to isolate the complete ORFs of seven groups of LMW-GS genes, respectively, and therefore possess great value for further research in the contributions of a single LMW-GS gene to wheat quality in the complex genetic background and the efficient selections of quality-related components in breeding programs.

Genetic variability of the low-molecular-weight glutenin subunits in spelt wheat (Triticum aestivum ssp. spelta L. em Thell.)

The low-molecular-weight glutenin subunit composition of a collection of 403 accessions of spelt wheat ( Triticum aestivum ssp. spelta L. em. Thell) was analyzed by SDS-PAGE. Extensive variation was found, including 46 different patterns for zone B and 16 for zone C. Patterns within zone B exhibited from two to six bands and patterns in zone C had between four and six bands in SDS-PAGE gels. A higher number of bands was observed when urea was added to the gels. Zone B exhibited between six and 11 bands, and we identified 14 new patterns in this zone. For zone C, up to ten new patterns that comprised between five and nine bands were detected. For both zones, 86 patterns were found. The variability detected in this material is greater than that detected in other hulled wheats.

Genetic improvement of plant for coeliac disease

Wheat, rye and barley are toxic for patients with coeliac disease. Toxicity has been found to result, respectively, from proteins such as gliadins, secalins and hordeins. Agglutination of in vitro cultured human myelogenous leukaemia K 562 (S) cells proved to be a suitable model for detection of toxic components of proteins. Five toxic peptides derived from an A-gliadin protein have been found to agglutinate the K 565 (S) cells. Triticum monococcum is a diploid wheat species widely grown during the Bronze Age. Proteins from monococcum are unable to agglutinate the K 562 (S) cells.

Biochemical and genetic characterisation of a D glutenin subunit encoded at the Glu-B3 locus

The SDS-PAGE pattern of reduced and alkylated glutenins from the bread wheat cultivar Prinqual presents a subunit (named d4) in the mobility zone of the omega -gliadins that only appears under reduced conditions. This subunit was isolated and characterised at the biochemical and genetic levels. Subunit d4 was shown to form disulphide aggregates with glutenins and had an acidic pI. These characteristics correspond to those of the D glutenin subunits. The N-terminal amino acid sequence of subunit d4 was coincident with the SRL sequence type characteristic of omega -gliadins encoded by genes on the 1B chromosome, and confirms the similarity between D glutenin subunits and omega -gliadins. The genetic study of subunit d4 was performed in the F2 progeny from the 'Prinqual' x 'Ablaca' cross, based on four prolamin loci: Glu-B1, Glu-B3, Gli-B1, and Gli-B5. The recombinants found between Glu-B3 and Gli-B1 demonstrated that subunit d4 was encoded at the Glu-B3 locus, and reinforces the hypothesis of the duplication of prolamin gene clusters in wheat. A preliminary study of the effect of subunit d4 on gluten strength showed that lines with the Glu-B3 allele from 'Prinqual', which includes subunit d4, had a significantly higher sedimentation volume than those with the allele from 'Ablaca'.Key words: wheat gluten proteins, D glutenin subunits, amino acid sequence, linkage mapping, complex loci duplication.

Inheritance of B subunits of glutenin and ω-and γ-gliadins in tetraploid wheats

A double-1RS wheat-rye translocation line lacking all B subunits of glutenin was produced in durum wheat cv 'Langdon' for use in backcrosses and testcrosses in the study of the inheritance of low-molecular-weight (LMW) glutenin subunits in tetraploid wheats. The B subunits of glutenin and γ-and ω-gliadin bands present in parents derived from Triticum durum and T. dicoccoides, encoded by Glu-3 and Gli-1 loci, respectively, were found to be inherited mainly as units (blocks), as reported previously. Two rare recombination events between the Glu-A3 and Gli-A1 loci were detected in testcross progeny from 'Edmore' x T. dicoccoides landrace 19-27. Several rare recombinants were also detected within the 1BS-controlled B subunits of glutenin blocks, suggesting that there are two separate tightly linked loci (3.07±1.35 cM) within the Glu-B3 'locus'. Evidence was also obtained for the presence of an additional locus coding for a B subunit of glutenin in 'Edmore' that is loosely linked (20.9±3.18%) with the main Glu-B3 'locus'.

Production and genetic characterization of near-isogenic lines in the bread-wheat cultivar Alpe

Two biotypes of the bread-wheat cultivar Alpe were shown to possess contrasting alleles at each of the glutenin (Glu-B1, Glu-D1, Glu-B3 and Glu-D3) and gliadin (Gli-B1 and Gli-D1) loci on chromosomes 1B and 1D. Fourteen near-isogenic lines (NILs) were produced by crossing these biotypes and used to determine the genetic control of both low-molecular-weight (LMW) glutenin subunits and gliadins by means of one-dimensional or two-dimensional electrophoresis. Genes coding for the B, C and D groups of EMW subunits were found to be inherited in clusters tightly linked with those controlling gliadins. Southern-blot analysis of total genomic DNAs hybridized to a γ-gliadin-specific cDNA clone revealed that seven NILs lack both the Gli-D1 and Glu-D3 loci on chromosome 1D. Segregation data indicated that these "null" alleles are normally inherited. Comparison of the "null" NILs with those possessing allele b at the Glu-D3 locus showed one B subunit, seven C subunits and two D subunits, as fractionated by two-dimensional A-PAGExSDS-PAGE, to be encoded by this allele. Alleles b and k at Glu-B3 were found to code for two C subunits plus eight and six B subunits respectively, whereas alleles b and k at Gli-B1 each controlled the synthesis of two β-gliadins, one γ and two ω-gliadins. The novel Gli-B5 locus coding for two ω-gliadins was shown to recombine with the Gli-B1 locus on chromosome 1B. The two-dimensional map of glutenin subunits showed α-gliadins encoded at the Gli-A2 locus on chromosome 6A. The use of Alpe NILs in the study of the individual and combined effects of glutenin subunits on dough properties is discussed.