Wheat storage proteins: their genetics and their potential for manipulation by plant breeding

Abstract

The genes that code for endosperm storage proteins occur at nine complex loci on six different chromosomes. Glu-A1, Glu-B1 and Glu-D1 contain the genes for high molecular mass subunits of glutenin and are close to the centromere on the long arms of chromosomes 1A, 1B and 1D respectively. On the short arms of the same chromosomes, but distant from the centromere, are Gli-A1, Gli-B1 and Gli-D1. Each of these loci carry three major gene families coding for $\omega$-gliadins, $\gamma$-gliadins and low molecular mass glutenin subunits. The remaining loci, Gli-A2, Gli-B2 and Gli-D2 occur near the ends of the short arms of chromosomes 6A, 6B and 6D respectively and each code for $\alpha$- and $\beta$-gliadins. Recombination of genes within a locus is very rare and has so far been detected only at Glu-B1, at the rate of about one recombinant in 1000 progeny. Each locus displays allelic variation and this is responsible for differences among varieties in protein quality for making bread. The protein variants that are associated with good quality are being identified, firstly by analysing segregating populations and secondly from the development of near-isogenic lines. Current, incomplete, information on the relative qualities of different alleles at each locus indicates the following order of importance: Glu-1 > Gli-1 > Gli-2. Landraces of primitive agriculture are being screened for novel proteins. The genes for some of them are being incorporated into the genomes of commercial wheats.