Quality traits. Gluten Strength
Contributed by Laura Pfluger (firstname.lastname@example.org)
The quality of wheat flour for bread making depends on the viscoelastic properties of the dough, which are influenced by the quantity and quality of the gluten-forming storage proteins of the endosperm.
These proteins consist of two classes, monomeric gliadins and polymeric glutenins, a classification based on the disulfide-bonding behavior of the individual proteins. The gliadins are monomeric proteins that either lack cysteine residues (omega gliadins) or have only intra-chain disulfide bonds. Glutenin subunits bind to each other forming polymers linked by disulphide bonds.
After reduction of disulfide bonds, glutenin subunits can be divided in two main groups: high molecular weight glutenin subunits (HMW-GS) and low molecular weight glutenin subunits (LMW-GS), based on the relatives mobilities in SDS-poyacrylamide gel electrophoresis (SDS-PAGE). Glutenin composition, especially that of the HMW-GS fraction, determines gluten strength and elasticity (1).
High Molecular Glutenins Loci
Three different loci, located on the long arms of group 1 chromosomes, code for the HMW-GS Glu-A1, Glu-B1 and Glu-D1. (2), whereas LMW-GS are coded by gene families located on the short arms of the same chromosomes.
The HMW-Gs can be classified according to their electrophoretic mobility, their structure and composition. Molecular analyses have shown that each Glu-1 locus contains two genes, one encoding a higher molecular weight x-type subunit, the other a lower molecular weight y-type subunit. Absence of subunits in some cases has been proved to be due to gene silencing. Most of the bread wheat cultivars possess from three to five active HMW-Gs. Usually, the Glu-D1 locus encodes both types, the Glu-B1 locus encoded both types or one x-type subunit, and the Glu-A1 locus can have one or none active subunits (3)
HMW-GS and Gluten Strength
In bread wheat, the first studies were concentrated on HMW-GS because they have a significant impact on dough cohesion and because they are easily identified by electrophoresis.
Payne et al. (4) discovered a correlation between the presence of certain HMW-GS and gluten strength, measured by the SDS-sedimentation volume test. On this basis, they designed a numeric scale to evaluate bread-making quality as a function of the described subunits (Glu-1 quality score) (4, 5). Assuming the effect of the alleles to be additive, the bread making quality was predicted by adding the scores of the alleles present in the particular line. It was established that the allelic variation at the Glu-D1 locus have a greater influence on bread-making quality than the variation at the others Glu-1 loci.
Different reports indicate that subunit combination 5+10 for locus Glu-D1 (Glu-D1 5+10) renders a stronger dough than Glu-D1 2+12. It has been suggested that the superior effect of the 5+10 pair of subunits compared to 2+12 is largely due to the presence of an extra cysteine residue in the Dx-5 subunit compared to the Dx-2 subunit, which would promote the formation of polymers with larger size distribution. Similarly, it has been postulated that differences in the number of cysteine residues are responsible for the larger amount of large-sized polymers associated with the 17+18 pair, when compared to the 20x + 20y pair (both are present at the Glu-B1 locus). The most striking difference between these two alleles is the lack of two cysteine residues in subunit 20 (6).
The variation on bread-making quality among different varieties cannot be explained only by the variation in HMW-GS composition. The LMW-GS (and in a smaller proportion the gliadins) and their interactions with the HMW-GS also play an important role in the determination of gluten strength and breadmaking quality.The 1BL/1RS rye translocation
Another factor that influence quality is the presence of certain wheat-rye translocations. Translocation of the short arm of rye chromosome 1R (1RS) confers to wheat resistance to a number of diseases and pathogens, and may enhance grain yield. 1RS has been transferred to wheat in the form of 1AL/1RS, 1BL/1RS and 1DL/1RS wheat-rye translocations. One of the most widely used translocation for breeding is the 1BL/1RS translocation.
The first step in analyzing gluten proteins is the protein extraction step. The gliadins are separated using A-PAGE electrophoresis, while glutenin are separated by SDS-PAGE with different polyacrylamide concentrations depending upon whether HMW or LMW glutenins need to be analyzed.
KASP markers are available for Glu-A1 and Glu-D1. For experimental details, follow the link on the left panel.
1. Functional properties of wheat glutenin. Weegels PL, Hamer RJ, Schofield ID. In: Journal of Cereal Science, 1996, 23:1-18. [abstract]
2. Genetics of wheat storage proteins and the effect of allelic variation on bread-making quality. Payne PI. In: Annual Reviews of Plant Physiology,1987, 38: 141-153.
3. Structural differences in allelic glutenin subunits of high and low Mr and their relationships with flour technological properties. Lafiandra D, Masci S, D’Ovidio R, Turchetta T, Margiotta B, Mac Ritchie F. In: Wheat structure: biochemistry and functionality. J.P. Schofield (ed.), 1995, The Royal Society of Chemistry. Special publication nº 212. pp. 117-127.
4. The relationship between HMW glutenin subunit composition and the bread-making quality of British-grown wheat varieties. Payne PI, Nigtingale MA, Krattiger AF, Holt LM.In: Journal of the Science of Food and Agriculture, 1987, 40:51-65.
5. The HMW glutenin subunit and gliadin compositions of German-Grown wheat varieties and their relationship with bread-making quality. Rogers WJ, Payne PI, Harinder K. In: Plant Breeding, 1989, 103:89-100.
6. Purification and characterisation of High Mr Glutenin subunit 20 and its Linked y-type subunit from durum wheat. Buonocore F, Caporale C, Lafiandra D. In: Journal of Cereal Science, 1996, 23:195-201. [abstract]
7. The challenge: one billion tons of wheat by 2020. Braun HJ, Payne TS, Morgunov AI, van Ginkel M, Rajaram S. In: Proc. 9th Int. Wheat Genet. Symp. A.E. Slinkard (ed.), 1998, Saskatoon, Canada.
8. Agronomic performance of chromosomes 1B and T1BL.1RS near-isolines in the spring bread wheat Seri M 82. Villareal RL, Banuelos O, Mujeeb-Kazi A, Rajaram S. In: Euphytica, 1998, 103: 195-202. [abstract]
9. Bread making quality and yield performance of 1BL/1RS wheat isogenic lines Bullrich L, Tranquilli G, Pfluger L, Suárez E, Barneix A. In: Plant Breeding, 1998, 117:119-122.
10. Root biomass, water-use efficiency and performance of wheat rye translocations of chromosomes 1 and 2 in spring bread wheat 'Pavon' . Ehdaie B, Whitkus RW, Waines JG. In: Crop Science, 2003, 43:710-717. [abstract]
11. 1RS translocation increases root biomass in Veery-type wheat isogenic lines and associates with grain yield . Ehdaie B, Waines JG. In: p 693-695. Proc. 10th. Intern. Wheat Genet. Symp. Paestum, Rome, Italy. N.E. Pogna ed.
12. Relationship between wheat high molecular weight glutenin subunit composition, 1RS translocations and sodium dodecyl sulfate sedimentation volume. Pflüger L, Suárez E, Lafiandra D. In: Journal of Genetics and Breeding, 1998, 52:271-279
13. Uneasy unions: quality effects of rye chromatin transfers to wheat. Graybosch RA. In: Journal of Cereal Science, 2001, 33:3-16 [abstract]