Transcriptome analysis reveals differentially expressed storage protein transcripts in seeds of Aegilops and wheat

Transcriptional profiles of developing grain of wheat and three Aegilops species (Ae. caudata, Ae. cylindrica, Ae. tauschii) were compared using an EST-based array procedure. This identified 22 genes which were over-expressed in all three Aegilops species, two of which were ‘weakly similar’ to avenin storage proteins of oats. Sequencing of the corresponding transcripts demonstrated that each corresponded to a small family of proteins called avenin-like a and b. Sequence comparisons demonstrated that these proteins belong to the ‘prolamin superfamily’ of plant proteins, with the closest relatives being the γ-gliadins and LMW subunits of wheat and avenins of oats. Furthermore, the type a and b proteins differ from each other in that the latter contain a duplicated sequence of about 120 residues. The a-type proteins clearly correspond to the LMW gliadins characterised previously. In contrast, proteins corresponding to the b-type sequences have not been previously characterized but may form part of the glutenin fraction and hence contribute to processing quality. The higher expression levels of the avenin-like proteins in Aegilops species and variation in the amino acid sequences of the b-type proteins between the species suggest that they could provide a source of variation for wheat improvement.