Detailed analysis of the expression of an alpha-gliadin promoter and the deposition of alpha-gliadin protein during wheat grain development

Background and Aims

Alpha-gliadin proteins are important for the industrial quality of bread wheat flour, but they also contain many epitopes that can trigger celiac (cœliac) disease (CD). The B-genome-encoded α-gliadin genes, however, contain very few epitopes. Controlling α-gliadin gene expression in wheat requires knowledge on the processes of expression and deposition of α-gliadin protein during wheat grain development.

Methods

A 592-bp fragment of the promotor of a B-genome-encoded α-gliadin gene driving the expression of a GUS reporter gene was transformed into wheat. A large number of transgenic lines were used for data collection. GUS staining was used to determine GUS expression during wheat kernel development, and immunogold labelling and tissue printing followed by staining with an α-gliadin-specific antibody was used to detect α-gliadin protein deposited in developing wheat kernels. The promoter sequence was screened for regulatory motifs and compared to other available α-gliadin promoter sequences.

Key Results

GUS expression was detected primarily in the cells of the starchy endosperm, notably in the subaleurone layer but also in the aleurone layer. The α-gliadin promoter was active from 11 days after anthesis (DAA) until maturity, with an expression similar to that of a 326-bp low molecular weight (LMW) subunit gene promoter reported previously. An α-gliadin-specific antibody detected α-gliadin protein in protein bodies in the starchy endosperm and in the subaleurone layer but, in contrast to the promoter activity, no α-gliadin was detected in the aleurone cell layer. Sequence comparison showed differences in regulatory elements between the promoters of α-gliadin genes originating from different genomes (A and B) of bread wheat both in the region used here and upstream.

Conclusions

The results suggest that additional regulator elements upstream of the promoter region used may specifically repress expression in the aleurone cell layer. Observed differences in expression regulator motifs between the α-gliadin genes on the different genomes (A and B) of bread wheat leads to a better understanding how α-gliadin expression can be controlled.Key words: Alpha-gliadin, promoter, expression, deposition, wheat, Triticum aestivum, grain development