Subunit 1Dx5 Research Articles

Molecular and Biochemical Characterisation of HMW Glutenin Subunits fromT. tauschiiand the D Genome of Hexaploid Wheat

Abstract Electrophoretic (urea SDS–PAGE) and chromatographic (RP–HPLC) analysis was performed on 8 allelic variants of HMW glutenin subunits derived from Triticum tauschii and from the D genome of a hexaploid wheat species ( Triticum macha ) and hexaploid landraces. These subunits had been previously identified using SDS–PAGE. The characterisation revealed that subunits Dy10 t and Dy12 t from T. tauschii could be differentiated from their bread wheat counterparts using both urea SDS–PAGE and RP–HPLC. In the latter case, the T. tauschii y-type subunits were clearly more hydrophobic than the Dy type subunits of bread wheat. The characterisation also suggested that subunit Dx5 t , derived from two separate T. tauschii accessions, did not contain the extra cysteine residue characteristic of Dx5 from bread wheat. RFLP analysis of the genes encoding the HMW glutenin subunits of interest suggested that the absence of Dx-type HMW glutenins in two hexaploid landraces was due to lack of expression of their encoding genes. The relationship between Hin dIII DNA fragment size and protein subunit size, as measured by electrophoretic mobility, is examined and discussed. Finally, the solubility properties of a HMW protein designated T1 (derived from T. tauschii accession AUS 18913) suggested that it was not a HMW glutenin subunit as was previously thought. Further studies are needed to clarify the identity of this subunit.

Characterisation of a Novel HighMrGlutenin Subunit Encoded by Chromosome 1D of Bread Wheat

Abstract A high M r subunit of wheat glutenin (1Dx2·2*), having an unusually high M r (approximately 110 000), was purified using a combination of preparative isoelectric focusing and reversed-phase high performance liquid chromatography. Comparison of its N -terminal sequence and amino acid composition with those of the allelic subunit 1Dx2 indicate that its greater M r could be due to the presence of a larger central repetitive domain. Spectrofluorimetric and circular dichroism analyses suggest that an increase in the length of this domain does not affect the conformational properties of the subunit.

Expression of individual HMW glutenin subunit genes of wheat (Triticum aestivum L.) in relation to differences in the number and type of homoeologous subunits and differences in genetic background

The amount of individual high-molecular-weight (HMW) glutenin subunits of bread-wheat has been studied in relation to variation at homoeologous loci and in the general genetic background. The relationships between Glu-1 loci have been studied using nearisogenic lines (NILs) of the variety Sicco and in the progenies of two crosses. Substitution of the Sicco Glu-D1 allele by a null-allele resulted in higher amounts of the homoeologous subunits. The presence of a Glu-A1 nullallele did not have a noticeable effect on the amounts of homoeologous subunits. In three out of four NILs and in the sister-lines of two crosses, the amounts of HMW-subunits did not depend on the allele make-up at homoeologous loci. Only in the NIL which contains the Glu-D1 allele, encoding subunits 1Dx2.2 and 1Dy12, was the amount of homoeologous subunits lower than the amount of these subunits in Sicco. This study suggests a relation between the amount of HMW-subunits encoded by an allele and its contribution to bread-making quality. The effect of genetic background has been studied using F4 and F5 lines of two crosses. The total amounts of subunits, relative to the total amount of kernel proteins, showed a considerable variation between lines. The ratio between individual subunits did not differ between genetic backgrounds. Because this ratio is also largely independent of differences in environmental conditions, it is concluded that the relative amount of a subunit is a valuable measure for the detection of genetically-determined differences in the expression of HMW-subunit genes.