Sequence heterogeneity and differential expression of the alpha-Amy2 gene family in wheat.

The alpha-Amy2 genes of wheat are a multigene family which is expressed in the aleurone cells of germinating grain under control of the plant hormone gibberellin. A subset of the genes are also expressed in developing grain. Comparison of five genomic clones containing alpha-Amy2 genes, using DNA sequence analysis and Southern hybridisation, showed that the extent of similarity between genes differed. Two of the most heterogeneous genes compared were located to the same group 7 chromosome while the most similar genes alpha-Amy2/54 and alpha-Amy2/8 were located to different ones; hence sequence variation could not be correlated to the ancestry of the alpha-Amy2 genes during the separate existence of the constituent genomes of hexaploid wheat. Expression of the cloned genes was measured using an S1 nuclease protection assay and this identified alpha-Amy2/54 and alpha-Amy2/8 as part of the subset of alpha-Amy2 genes expressed in both the developing grain and in aleurone cells. Comparison of the 5' upstream regions of all five genes showed high similarity, with the exception of one gene, up to -280 nucleotides from the transcriptional start, while similarity between alpha-Amy2/54 and alpha-Amy2/8 extended a further 90 bp upstream of this point. It is suggested that regulatory elements responsible for tissue specificity and gibberellin regulation may be located within these regions of similarity.