Expression of HMW Subunit, γ-Zein and uidA Genes in Endosperms of Transgenic Bread Wheat

Abstract

Transformation allows the production of wheat plants with specific differences in their gluten structure, by the introduction of additional genes for wild type or mutant proteins Similarly, genes from other species can also be inserted, such as those for the γ-zein proteins which are associated with hard endosperm texture in maize. It therefore allows the relationships between protein composition and grain functionality to be established. Transgenic wheat lines were obtained by transformation with genes encoding wild type subunit 1Dx5, long and short mutant forms of this subunit and subunit Dx2.2*, using particle bombardment. The mutant HMW subunit constructs differ in the lengths of their repetitive domain while subunit 1Dx2.2* is the largest HMW glutenin subunit reported. These genes will therefore provide information on the relationship between subunit structure and gluten properties. Expression of the wild type and mutant forms of subunit 1Dx5 has been shown by SDS-PAGE of seed proteins. Small-scale Mixograph analysis and other testing of flour from these lines will be carried out to determine changes in functional properties. In a related study, transgenic wheat plants with the γ-zein gene driven by either the wheat HMW subunit promoter or the maize γ-zein promoter were produced. Analysis of the seed proteins of several γ-zein PCR-positive lines, by dot blotting and antibody hybridisation and SDS-PAGE, has shown the expression of the γ-zein gene. To study the tissue specificity, several homozygous transgenic plants were produced with the uidA gene driven by the HMW subunit promoter. GUS expression was observed in starchy endosperms of transgenic plants in the T₁, T₂ and T₃ generations, but not in leaves, roots, anthers and pollen, demonstrating endosperm-specific expression regulated by the HMW subunit promoter.