The structure and genetic control of a new class of disulphide-linked proteins in wheat endosperm

Association of High and Low Molecular Weight Glutenin Subunits with Gluten Strength in Tetraploid Durum Wheat (Triticum turgidum spp. Durum L.)

The gluten strength and the composition of high- and low-molecular-weight glutenin subunits (HMWGSs and LMWGSs) of fifty-one durum wheat genotypes were evaluated using sodium dodecyl sulfate (SDS) sedimentation testing and SDS polyacrylamide gel electrophoresis (SDS-PAGE). This study examined the allelic variability and the composition of HMWGSs and LMWGSs in T. durum wheat genotypes. SDS-PAGE was proven to be a successful method for identifying HMWGS and LMWGS alleles and their importance in determining the dough quality. The evaluated durum wheat genotypes with HMWGS alleles 7+8, 7+9, 13+16, and 17+18 were highly correlated with improved dough strength. The genotypes containing the LMW-2 allele displayed stronger gluten than those with the LMW-1 allele. The comparative in silico analysis indicated that Glu-A1, Glu-B1, and Glu-B3 possessed a typical primary structure. The study also revealed that the lower content of glutamine, proline, glycine, and tyrosineand the higher content of serine and valine in the Glu-A1 and Glu-B1 glutenin subunits, and the higher cysteine residues in Glu-B1 and lower arginine, isoleucine, and leucine in the Glu-B3 glutenin, are associated with the suitability of durum wheat for pasta making and the suitability of bread wheat with good bread-making quality. The phylogeny analysis reported that both Glu-B1 and Glu-B3 had a closer evolutionary relationship in bread and durum wheat, while the Glu-A1 was highly distinct. The results of the current research may help breeders to manage the quality of durum wheat genotypes by exploiting the allelic variation in glutenin. Computational analysis showed the presence of higher proportions of glutamine, glycine, proline, serine, and tyrosine than the other residues in both HMWGSs and LMWGSs. Thus, durum wheat genotype selection according to the presence of a few protein components effectively distinguishes the strongest from the weakest types of gluten.

Predicting Hybrid Performances for Quality Traits through Genomic-Assisted Approaches in Central European Wheat

Bread-making quality traits are central targets for wheat breeding. The objectives of our study were to (1) examine the presence of major effect QTLs for quality traits in a Central European elite wheat population, (2) explore the optimal strategy for predicting the hybrid performance for wheat quality traits, and (3) investigate the effects of marker density and the composition and size of the training population on the accuracy of prediction of hybrid performance. In total 135 inbred lines of Central European bread wheat (Triticum aestivum L.) and 1,604 hybrids derived from them were evaluated for seven quality traits in up to six environments. The 135 parental lines were genotyped using a 90k single-nucleotide polymorphism array. Genome-wide association mapping initially suggested presence of several quantitative trait loci (QTLs), but cross-validation rather indicated the absence of major effect QTLs for all quality traits except of 1000-kernel weight. Genomic selection substantially outperformed marker-assisted selection in predicting hybrid performance. A resampling study revealed that increasing the effective population size in the estimation set of hybrids is relevant to boost the accuracy of prediction for an unrelated test population.

Functional cereals for production in new and variable climates

Adaptation of cereal crops to variable or changing climates requires that essential quality attributes are maintained to deliver food that will be acceptable to human consumers. Advances in cereal genomics are delivering insights into the molecular basis of nutritional and functional quality traits in cereals and defining new genetic resources. Understanding the influence of the environment on expression of these traits will support the retention of these essential functional properties during climate adaptation. New cereals for use as whole grain or ground to flour for other food products may be based upon the traditional species such as rice and wheat currently used in these food applications but may also include new options exploiting genomics tools to allow accelerated domestication of new species.

Deciphering the complexities of the wheat flour proteome using quantitative two-dimensional electrophoresis, three proteases and tandem mass spectrometry

BACKGROUND

Wheat flour is one of the world's major food ingredients, in part because of the unique end-use qualities conferred by the abundant glutamine- and proline-rich gluten proteins. Many wheat flour proteins also present dietary problems for consumers with celiac disease or wheat allergies. Despite the importance of these proteins it has been particularly challenging to use MS/MS to distinguish the many proteins in a flour sample and relate them to gene sequences.

RESULTS

Grain from the extensively characterized spring wheat cultivar Triticum aestivum 'Butte 86' was milled to white flour from which proteins were extracted, then separated and quantified by 2-DE. Protein spots were identified by separate digestions with three proteases, followed by tandem mass spectrometry analysis of the peptides. The spectra were used to interrogate an improved protein sequence database and results were integrated using the Scaffold program. Inclusion of cultivar specific sequences in the database greatly improved the results, and 233 spots were identified, accounting for 93.1% of normalized spot volume. Identified proteins were assigned to 157 wheat sequences, many for proteins unique to wheat and nearly 40% from Butte 86. Alpha-gliadins accounted for 20.4% of flour protein, low molecular weight glutenin subunits 18.0%, high molecular weight glutenin subunits 17.1%, gamma-gliadins 12.2%, omega-gliadins 10.5%, amylase/protease inhibitors 4.1%, triticins 1.6%, serpins 1.6%, purinins 0.9%, farinins 0.8%, beta-amylase 0.5%, globulins 0.4%, other enzymes and factors 1.9%, and all other 3%.

CONCLUSIONS

This is the first successful effort to identify the majority of abundant flour proteins for a single wheat cultivar, relate them to individual gene sequences and estimate their relative levels. Many genes for wheat flour proteins are not expressed, so this study represents further progress in describing the expressed wheat genome. Use of cultivar-specific contigs helped to overcome the difficulties of matching peptides to gene sequences for members of highly similar, rapidly evolving storage protein families. Prospects for simplifying this process for routine analyses are discussed. The ability to measure expression levels for individual flour protein genes complements information gained from efforts to sequence the wheat genome and is essential for studies of effects of environment on gene expression.

Comparative proteome analysis of metabolic proteins from seeds of durum wheat (cv. Svevo) subjected to heat stress

In Central and Southern Italy, where durum wheat represents one of the most widely cultivated crops, grain filling occurs during Spring, a period characterized by sudden increases in temperature. Wheat grain proteins are classified into albumins, globulins, and prolamins. The nonprolamin fractions include proteins with metabolic activity or structural function. In order to investigate the consequences of heat stress on the accumulation of nonprolamin proteins in mature durum wheat kernels, the Italian cultivar Svevo was subjected to two thermal regimes (heat stress versus control). The 2-D patterns of nonprolamin proteins were monitored to identify polypeptides affected by heat stress during grain fill. This study shows that heat stress alters significantly the durum wheat seed proteome, although the changes range is only between 1.2- and 2.2-fold. This analysis revealed 132 differentially expressed polypeptides, 47 of which were identified by MALDI-TOF and MALDI-TOF-TOF MS and included HSPs, proteins involved in the glycolysis and carbohydrate metabolism, as well as stress-related proteins. Many of the heat-induced polypeptides are considered to be allergenic for sensitive individuals.

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.

Isolation of wheat–rye 1RS recombinants that break the linkage between the stem rust resistance gene SrR and secalin

Chromosome 1R of rye is a useful source of genes for disease resistance and enhanced agronomic performance in wheat. One of the most prevalent genes transferred to wheat from rye is the stem rust resistance gene Sr31. The recent emergence and spread of a stem rust pathotype virulent to this gene has refocused efforts to find and utilize alternative sources of resistance. There has been considerable effort to transfer a stem rust resistance gene, SrR, from Imperial rye, believed to be allelic to Sr31, into commercial wheat cultivars. However, the simultaneous transfer of genes at the Sec-1 locus encoding secalin seed storage proteins and their association with quality defects preclude the deployment of SrR in some commercial wheat breeding programs. Previous attempts to induce homoeologous recombination between wheat and rye chromosomes to break the linkage between SrR and Sec-1 whilst retaining the tightly linked major loci for wheat seed storage proteins, Gli-D1 and Glu-D3, and recover good dough quality characteristics, have been unsuccessful. We produced novel tertiary wheat–rye recombinant lines carrying different lengths of rye chromosome arm 1RS by inducing homoeologous recombination between the wheat 1D chromosome and a previously described secondary wheat–rye recombinant, DRA-1. Tertiary recombinant T6-1 (SrR+ Sec-1–) carries the target gene for stem rust resistance from rye and retains Gli-D1 but lacks the secalin locus. The tertiary recombinant T49-7 (SrR– Sec-1+) contains the secalin locus but lacks the stem rust resistance gene. T6-1 is expected to contribute to wheat breeding programs in Australia, whereas T49-7 provides opportunities to investigate whether the presence of secalins is responsible for the previously documented dough quality defects.

[Isolation and characterization of a low molecular weight glutenin gene from Taenitherum Nevski]

More and more low-molecular-weight glutenin(LMW glutenin) genes were isolated and characterized from hexaploid wheat (Triticum aestivum L.). However, few homologous genes were obtained from its relative species, which limited our understanding of the relationships among them. Therefore, it is necessary to isolate LMW glutenin homologous genes from wheat wild relative species. Using a pair of specific oligonucleotide PCR primers for Taenitherum genomic DNA, a LMW glutenin gene sequence, with nucleotide sequence in 1 035 bp and deduced amino acid sequence with 343 amino acid residues, was obtained. This sequence was a typical LMW glutenin sequence and characterized by a signal peptide of 21 amino acid residues, a N-terminal conservative domain of 13 amino acid residues, a repetitive domain of short peptide, and a C-terminal conservative domain. Sequence alignment showed the main differences and the relationships between LMW glutenin genes from wheat and Taenitherum. The results presented here give a reference to isolate LMW glutenin gene from Taenitherum, as well as other wheat wild relatives.

Genetic evaluation of several physiological traits for screening of suitable spring safflower (Carthamus tinctorius L.) genotypes under stress and non-stress irrigation regimes

Seven cultivars and one line of spring safflower (Carthamus tinctorius L.) were used to estimate genetic variation, heritability, genetic gain and genetic factor analysis for several physiological traits. Each experiment was conducted in a randomized complete block design with three replications. Factor loadings in first factor were used for determination of important physiological traits for suitable genotype screening under each irrigation regimes. Under non-stress conditions, factor analysis technique extracted six factors which exploited about 93% of the total genetic variation, while 30% of the total genetic variance was associated by the first factor. Under stress conditions factor analysis extracted four factors and they totally explained 100% of the total genetic variation, while, the first factor accounted for 38% of the total genetic variation. Ultimate, leaf area index (at stem-elongation and flowering), leaf osmotic potential (at stem-elongation) and rate of water loss from excised leaves (at flowering) under non-stress conditions and also leaf area index (at flowering and grain filling) and rate of water loss from excised leaves (at grain filling) under stress conditions were the best criteria for screening of suitable genotype under explicated conditions.

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.

Classification of wheat low-molecular-weight glutenin subunit genes and its chromosome assignment by developing LMW-GS group-specific primers

On the basis of sequence analysis, 69 known low-molecular-weight glutenin subunit (LMW-GS) genes were experimentally classified into nine groups by the deduced amino acid sequence of the highly conserved N-terminal domain. To clarify the chromosomal locations of these groups, 11 specific primer sets were designed to carry out polymerase chain reactions (PCR) with the genomic DNA of group 1 ditelosomic lines of Chinese Spring, among which nine primer sets proved to be LMW-GS group-specific. Each group of LMW-GS genes was specifically assigned on a single chromosome arm and hence to a specific locus. Therefore, these results provided the possibility to predict the chromosome location of a new LMW-GS gene based on its deduced N-terminal sequence. The validity of the classification was confirmed by the amplifications in 27 diploid wheat and Aegilops accessions. The length polymorphisms of LMW-GS genes of groups 1 and 2, and groups 3 and 4.1 were detected in diploid A-genome and S-genome accessions, respectively. The diploid wheat and Aegilops species could be used as valuable resources of novel allele variations of LMW-GS gene in the improvement of wheat quality. The nine LMW-GS group-specific primer sets could be utilized to select specific allele variations of LMW-GS genes in the marker-assisted breeding.

Cereal seed storage proteins: structures, properties and role in grain utilization

Storage proteins account for about 50% of the total protein in mature cereal grains and have important impacts on their nutritional quality for humans and livestock and on their functional properties in food processing. Current knowledge of the structures and properties of the prolamin and globulin storage proteins of cereals and their mechanisms of synthesis, trafficking and deposition in the developing grain is briefly reviewed here. The role of the gluten proteins of wheat in determining the quality of the grain for breadmaking and how their amount and composition can be manipulated leading to changes in dough mixing properties is also discussed.

Genetic and biochemical characterization of novel low molecular weight glutenin subunits in wheat (Triticum aestivum L.)

Two novel low molecular weight subunits of glutenin with relative molecular mass (M(r) values) of 30 and 32 kDa were isolated from the seeds of hexaploid wheat and characterized at genetic and biochemical levels. Among 115 Indian bread wheat cultivars analysed, 40 had a narrow doublet of the new protein bands, 69 had a wide doublet, 3 had only the faster moving band of the doublet, and the remaining 3 cultivars had only the slower moving band. These subunits could be seen in the alkylated glutenin preparations only and the genes for the faster (designated Glu-D4) and slower (designated Glu-D5) moving protein bands of the doublet were located on chromosomes 1D and 7D, respectively. Amino acid composition of the two new subunits was quite different from those of the other well-characterized gluten proteins, as the new subunits have lower amounts of proline and relatively higher amounts of glycine, aspartic acid-asparagine, cysteine, and lysine. Polyclonal antibodies raised against these polypeptides cross-reacted strongly with the major low molecular weight subunits of wheat glutenin (Glu-3 subunits), but did not cross-react with the high molecular weight glutenin subunits or monomeric gliadins. Furthermore, preliminary results on the N-terminal amino acid sequences of the new subunits show homology with the major low molecular weight glutenin subunits, suggesting an evolutionary link between the two.

Conversion of a RAPD-generated PCR product, containing a novel dispersed repetitive element, into a fast and robust assay for the presence of rye chromatin in wheat

Bulk segregant analysis was used to obtain a random amplified polymorphic DNA (RAPD) marker specific for the rye chromosome arm of the 1BL.1RS translocation, which is common in many high-yielding bread wheat varieties. The RAPD-generated band was cloned and end-sequenced to allow the construction of a pair of oligonucleotide primers that PCR-amplify a DNA sequence only in the presence of rye chromatin. The amplified sequence shares a low level of homology to wheat and barley, as judged by the low strength of hybridization of the sequence to restriction digests of genomic DNA. Genetic analysis showed that the amplified sequence was present on every rye chromosome and not restricted to either the proximal or distal part of the 1RS arm. In situ hybridization studies using the amplified product as probe also showed that the sequence was dispersed throughout the rye genome, but that the copy number was greatly reduced, or the sequence was absent at both the centromere and the major sites of heterochromatin (telomere and nucleolar organizing region). The probe, using both Southern blot and in situ hybridization analyses, hybridized at a low level to wheat chromosomes, and no hybridizing restriction fragments could be located to individual wheat chromosomes from the restriction fragment length polymorphism (RFLP) profiles of wheat aneuploids. The disomic addition lines of rye chromosomes to wheat shared a similar RFLP profile to one another. The amplified sequence does not contain the RIS 1 sequence and therefore represents an as yet undescribed dispersed repetitive sequence. The specificity of the amplification primers is such that they will provide a useful tool for the rapid detection of rye chromatin in a wheat background. Additionally, the relatively low level of cross-hybridization to wheat chromatin should allow the sequence to be used to analyse the organization of rye euchromatin in interphase nuclei of wheat lines carrying chromosomes, chromosome segments or whole genomes derived from rye.

Destaining of Coomassie Brilliant Blue R-250-stained polyacrylamide gels with sodium chloride solutions

A novel method for destaining of polyacrylamide gels, stained with Coomassie Brilliant Blue R-250, is described, based on the use of 0.5 M NaCl in water as the destainer, requiring only 2-3 h. Concentrated (> 2 M) or dilute (< 0.1 M) salt solutions were unsuitable. The method affords the advantage that expensive organic solvents, such as methanol, acetic acid or trichloroacetic acid, are not needed. Furthermore, salt destaining results in darker purple-blue protein bands as compared to the pale blue color with e.g. methanol/acetic acid destaining.

Predigestion of DNA template improves the level of polymorphism of random amplified polymorphic DNAs in wheat

Random amplified polymorphic DNA (RAPD) analysis in wheat has proven to be poor in its levels of both reproducibility and polymorphism. By digesting the template, prior to performing PCR, with frequently cutting restriction enzymes, the level of polymorphism was improved. RAPD profiles from certain primers were not affected by this pretreatment of the template, but other primers produced distinct profiles from each of several restriction enzymes assayed. Some polymorphisms were specific to one or more restriction digests, but none involved the simple loss of bands from the unrestricted template profile. Genotypic comparisons enabled the selection of primer-restriction enzyme combinations that enabled polymorphic and mappable patterns to be produced both between wheat varieties and between wheats with and without chromosomal segments deriving from related species.

Our obsession with high resolution in gel electrophoresis: does it necessarily give the right answer?

Poor resolution of protein zones in an electrophoretic pattern may not necessarily be the result of poor technique. The example is given of the 'streak material', extracted from wheat flour, now recognised to be aggregated subunits of glutenin. The size distribution of the aggregated glutenin 'streak' is the key to elucidating the functional properties of wheaten dough. A stepped-layer gel technique has been devised to quantitate the proportions of aggregated glutenin in specific size groupings.

A rice protein library: a data-file of rice proteins separated by two-dimensional electrophoresis

Proteins extracted from embryos, endosperms and leaves of rice were separated by two-dimensional electrophoresis and relative molecular weights and isoelectric points were determined. The separated proteins were electroblotted onto a polyvinylidene difluoride membrane and 85 electroblotted proteins were analyzed by a gas-phase protein sequencer. The N-terminal amino-acid sequences of 27 out of 85 proteins were determined in this manner. The N-terminal regions of the remaining proteins could not be sequenced and they were inferred to have a blocking group at the N-terminus. Among proteins, 11 could be sequenced after deblocking by in situ treatment with pyroglutamyl peptidase. The internal amino-acid sequences of 23 proteins were determined by sequence analysis of peptides obtained by Cleveland peptide mapping. The amino-acid sequences determined here were compared with those of known plant and animal proteins. The concanavalin A-peroxidase method was used to determine whether the 85 proteins were glycosylated and the diagonal electrophoresis method was used to determine whether they contained disulphide bonding. Finally, we constructed a data-file of rice proteins including information on relative molecular weight, isoelectric point, amino-acid sequence, sequence homology, glycosylation, and the presence of disulphide bonding.

Isolation and characterization of wheat triticin cDNA revealing a unique lysine-rich repetitive domain

Polyclonal antibodies were raised against a purified 22 kDa triticin polypeptide (delta) and were used to screen a wheat seed cDNA library in the Escherichia coli expression vector lambda gt11. The isolated cDNA clones were grouped into three families based on their cross-hybridization reactions in DNA dot-blot studies. Southern blots of genomic DNAs extracted from ditelocentric and nullisomic-tetrasomic lines of Chinese Spring wheat, probes with the excised cDNA inserts, indicated that one of the three families (9 clones) had triticin clones. This was finally confirmed by comparing the predicted amino acid sequences of two of these clones (lambda Tri-12, lambda Tri-25) with the published tryptic peptide sequences of triticin. The Southern blots also showed that there is at least one triticin gene located on the short arm of each of the homoeologous group 1 chromosomes (1A, 1B, 1D), although till now no triticin protein product has been identified for the chromosome 1B. The nucleotide sequence of the largest triticin cDNA clone lambda Tri-25 (1567 bp) is presented here, and its predicted amino acid sequence shows strong homology with the legumin-like proteins of oats (12S globulin), rice (glutelin) and legume seeds. A unique feature of the triticin sequence is that it contains a lysine-rich repetitive domain, inserted in the hypervariable region of the typical legumin-like genes. Northern blotting of total RNA extracted from different stages of the developing wheat seed revealed that the triticin gene expression is switched on 5-10 days after anthesis (DAA). There was a steady increase in the level of triticin mRNA until 20 DAA, after which it started decreasing. The maximum mRNA accumulation occurred between 17 and 20 DAA. These observations conform closely with the published data on triticin protein accumulation during grain development.

Production of multiple wheat-rye 1RS translocation stocks and genetic analysis of LMW subunits of glutenin and gliadins in wheats using these stocks

A triple (1AL.1RS/1BL.1RS/1DL.1RS) and three double (1AL.1RS/1BL.1RS, 1AL.1RS/1DL.1RS, 1BL.1RS/1DL.1RS) wheat-rye 1RS translocation stocks were isolated from a segregating population using the Gli-1, Tri-1 and Sec-1 seed proteins as genetic markers. These stocks carried 42 chromosomes and formed the expected multivalents (frequency of 14-25%) at metaphase 1. They gave floret fertility ranging from 40-60%. These stocks were subsequently used to determine the genetic control of low-molecular-weight (LMW) glutenin subunits in 'Chinese Spring' and 'Gabo' by means of two-step one-dimensional SDS-PAGE. All of the B subunits and most of the C subunits of glutenin were shown to be controlled by genes on the short arms of group-1 chromosomes in these wheats. The other C subunits were not controlled by group-1 chromosomes. The triple translocation line served as a suitable third parent in producing test-cross seeds for studying the inheritance of the LMW glutenin subunits and gliadins in wheat cultivars, e.g. 'Chinese Spring' and 'Orca'. The segregation patterns of the LMW glutenin subunits in these cultivars revealed that the subunits were inherited in clusters and that their controlling genes (Glu-3) were tightly linked with those controlling gliadins (Gli-1). The LMW glutenin patterns d, d and e in 'Orca' segregated as alternatives to the patterns a, a and a in 'Chinese Spring' controlled by Glu-A3, Glu-B3 and Glu-D3 loci on chromosome arms 1AS, 1BS and 1DS, respectively, thus indicating that these patterns were controlled by allelic genes at these loci.

Isolation and characterization of wheat-rye recombinants involving chromosome arm 1DS of wheat

The introgression of genetic material from alien species is assuming increased importance in wheat breeding programs. One example is the translocation of the short arm of rye chromosome 1 (1RS) onto homoeologous wheat chromosomes, which confers disease resistance and increased yield on wheat. However, this translocation is also associated with dough quality defects. To break the linkage between the desirable agronomic traits and poor dough quality, recombination has been induced between 1RS and the homoeologous wheat arm IDS. Seven new recombinants were isolated, with five being similar to those reported earlier and two havina new type of structure. All available recombinantsw ere characterized with DNA probes for the loci Nor-R1, 5SDna-R1, and Tel-R1. Also, the amount of rye chromatin present was quantified with a dispersed rye-specific repetitive DNA sequence in quantitative dot blots. Furthermore, the wheat-rye recombinants were used as a mapping tool to assign two RFLP markers to specific regions on chromosome arms 1DS and 1RS of wheat and rye, respectively.

Linkage mapping of genes for resistance to leaf, stem and stripe rusts and ω-secalins on the short arm of rye chromosome 1R

The genes controlling resistance to three wheat rusts, viz., leaf rust (Lr26), stem rust (Sr31) and stripe or yellow rust (Yr9), and ω-secalins (Sec1), located on the short arm of rye chromosome 1R, were mapped with respect to each other and the centromere. Analysis of 214 seeds (or families derived from them) from testcrosses between a 1BL.1RS/1R heterozygote and 'Chinese Spring' ditelocentric 1BL showed no recombination between the genes for resistance to the three rusts, suggesting very tight linkage or perhaps a single complex locus conferring resistance to the three rusts. The rust resistance genes were located 5.4 ± 1.7 cM from the Sec1 locus, which in turn was located 26.1 ± 4.3 cM from the centromere; the gene order being centromere - Sec1 - Lr26/Sr31/Yr9 - telomere. In a second test-cross, using a different 1BL.1RS translocation which had only stem rust resistance (SrR), the above gene order was confirmed despite a very large proportion of aneuploids (45.8%) among the progeny. Furthermore, a map distance of 16.0 ± 4.8 cM was estimated for SrR and the telomeric heterochromatin (C-band) on 1RS. These results suggest that a very small segment of 1RS chromatin is required to maintain resistance to all three wheat rusts. It should be possible but difficult to separate the rust resistance genes from the secalin gene(s), which are thought to contribute to dough stickiness of wheat-rye translocation lines carrying 1RS.

Two-step one-dimensional SDS-PAGE analysis of LMW subunits of glutelin : 1. Variation and genetic control of the subunits in hexaploid wheats

A collection of 222 hexaploid wheat cultivars (including the 207 cultivars studied by Gupta and Shepherd in 1988) from 32 countries was analyzed for variation in the banding patterns of LMW subunits of glutenin using a modified two-step 1-D SDS-PAGE. Seventy percent ethanol at high temperature (≥50 °C) was used to selectively dissolve the native glutenins containing A, B, and C subunits and not the albumins and globulins (non-prolamins). This procedure allowed the glutenin subunits A, B and C to be separated in a background free of albumins and globulins, which normally overlap the B and C subunits (LMW subunits of glutenin). Although 40 different B and C subunits were detected, except where the cultivars carried a 1BL-1RS translocation or 1B/1R substitution, each cultivar exhibited from 7 to 16 subunits. These subunits could be divided into 20 band patterns which fell into three groups on the basis of their mutual exclusiveness, with 6, 9, and 5 patterns. Analysis of substitution lines revealed that the different patterns in these groups are controlled by genes on chromosomes 1A, 1B, and 1D, respectively. The least number of subunits was controlled by chromosome 1A and approximately 40% of the cultivars did not contain any band controlled by this chromosome. Thirteen of the cultivars were found to consist of two biotypes with respect to LMW subunits of glutenin. The genetic, evolutionary, and technological implications of these findings are discussed.