Breadmaking is one of humankind's oldest technologies, being established some 4,000 years ago. The ability to make leavened bread depends largely on the visco-elastic properties conferred to wheat doughs by the gluten proteins. These allow the entrapment of carbon dioxide released by the yeast, giving rise to a light porous structure. One group of gluten proteins, the high molecular weight (HMW) subunits, are largely responsible for gluten elasticity, and variation in their amount and composition is associated with differences in elasticity (and hence quality) between various types of wheat. These proteins form elastomeric polymers stabilized by inter-chain disulphide bonds, and detailed studies of their structures have led to models for the mechanism of elasticity. This work has also provided a basis for direct improvement of wheat quality by transformation with additional HMW subunit genes.

The maize (Zea mays) Viviparous 1 (Vp1) transcription factor has been shown previously to be a major regulator of seed development, simultaneously activating embryo maturation and repressing germination. Hexaploid bread wheat (Triticum aestivum) caryopses are characterized by relatively weak embryo dormancy and are susceptible to preharvest sprouting (PHS), a phenomenon that is phenotypically similar to the maize vp1 mutation. Analysis of Vp-1 transcript structure in wheat embryos during grain development showed that each homeologue produces cytoplasmic mRNAs of different sizes. The majority of transcripts are spliced incorrectly, contain insertions of intron sequences or deletions of coding region, and do not have the capacity to encode full-length proteins. Several VP-1-related lower molecular weight protein species were present in wheat embryo nuclei. Embryos of a closely related tetraploid species (Triticum turgidum) and ancestral diploids also contained misspliced Vp-1 transcripts that were structurally similar or identical to those found in modern hexaploid wheat, which suggests that compromised structure and expression of Vp-1 transcripts in modern wheat are inherited from ancestral species. Developing embryos from transgenic wheat grains expressing the Avena fatua Vp1 gene showed enhanced responsiveness to applied abscisic acid compared with the control. In addition, ripening ears of transgenic plants were less susceptible to PHS. Our results suggest that missplicing of wheat Vp-1 genes contributes to susceptibility to PHS in modern hexaploid wheat varieties and identifies a possible route to increase resistance to this environmentally triggered disorder.T he Viviparous1 (Vp1) gene is a major regulator of late embryo development in maize. Inactivation of this locus leads to disruption of embryo maturation, resulting in the promotion of germination of embryos while still attached to the cob (vivipary). The phenotypes of vp1 mutants show that this locus performs two distinct functions: to promote embryo maturation and embryo dormancy and simultaneously to repress germination (1, 2). Specific genes and enzyme activities have been identified that are activated or repressed by Vp1 in vivo. Expression of several enzymes (3) and maturation-related genes (4) is reduced in the mutants including those encoding seed-storage proteins and diverse LEA (late embryogenesis-abundant) proteins (1). On the other hand, ␣-amylase activity increases in the same mutants during aleurone maturation (3). These observations indicate a bifunctional role for Vp1 in regulating the balance between the activation of embryo-maturation genes and the repression of germinative hydrolases during kernel development and maturation.Orthologues of Vp1 have been cloned from rice [Osvp1 (4)], wild oat [AfVp1 (5)], and several dicotyledonous species such as Arabidopsis [ABI3 (6)] and poplar [PtABI3 (7)]. Vp1 homeologues have been mapped in wheat to the long arms of the group 3 chromosomes at a location conserved relative to Vp1 in maize and Osvp1 ...

The high molecular weight (HMW) subunits of wheat glutenin are major determinants of the elastic properties of gluten that allow the use of wheat doughs to make bread, pasta, and a range of other foods. There are both quantitative and qualitative effects of HMW subunits on the quality of the grain, the former being related to differences in the number of expressed HMW subunit genes. We have transformed bread wheat in order to increase the proportions of the HMW subunits and improve the functional properties of the flour. A range of transgene expression levels was obtained with some of the novel subunits present at considerably higher levels than the endogenous subunits. Analysis of T2 seeds expressing transgenes for one or two additional HMW subunits showed stepwise increases in dough elasticity, demonstrating the improvement of the functional properties of wheat by genetic engineering.