A second ‘overexpression’ allele at the Glu-B1 high-molecular-weight glutenin locus of wheat: sequence characterisation and functional effects
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Bread is one of the major constituents of the human diet and wheat (Triticum aestivum L.) is the most important cereal for bread making. The gluten proteins (glutenins and gliadins) are recognised as important components affecting the processing quality of wheat flour. In this research, we investigated a particular glutenin subunit allele in an Australian cultivar, H45. Based on protein and DNA assays, the Glu-B1 allele of H45 seems to be Glu-B1al, an allele that includes a functional duplication of a gene encoding an x-type high-molecular-weight glutenin subunit, and is thought to increase dough strength through overexpression of that subunit. Yet H45 does not have the dough properties that would be expected if it carries the Glu-B1al allele. After confirming that H45 overexpresses Bx subunits and that it has relatively low un-extractable polymeric protein (an indicator of weak dough), we cloned and sequenced two Bx genes from H45. The sequences of the two genes differ from each other, and they each differ by four single-nucleotide polymorphisms (SNPs) from the sequence that has been reported for the Glu-B1al x-type glutenin genes of the Canadian wheat cultivar Glenlea. One of the SNPs leads to an extra cysteine residue in one of the subunits. The presence of this additional cysteine may explain the dough properties of H45 through effects on cross-linkage within or between glutenin subunits. We propose that the Glu-B1 allele of H45 be designated Glu-B1br, and we present evidence that Glu-B1br is co-inherited with low un-extractable polymeric protein.
The authors thank Dr Haydn Kuchel for drawing our attention to the properties of H45, Dr Howard Eagles for valuable advice, including the suggestion of VQ0437 as a useful control, Dr Russell Eastwood for providing seed of VQ0437, Dr Karen Cane for providing protocols for assaying puroindoline, serpin and Spa-B alleles, Dr Robert Dickinson for assistance with preparation of the figures, the Premier’s Science and Research Fund of South Australia and the Molecular Plant Breeding Cooperative Research Centre for financial support and the China Scholarship Council and the University of Adelaide for a scholarship awarded to the first author.
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