α-amylase genes of wheat are two multigene families which are differentially expressed

The α-Amy1 and α-Amy2 genes of wheat produce distinct subsets of α-amylase isozymes which show different patterns of expression in wheat aleurone cells and in developing grain. In order to characterise the organisation and expression of these genes, clones of α-Amy1 and α-Amy2 cDNA have been isolated. The two types of cDNA clone were distinguished within a small library of α-amylase cDNA clones (Baulcombe and Buffard, Planta 157 493-501 [1983]) by restriction endonuclease mapping and by cross hybridisation. The identity of α-Amy1 or α-Amy2 type was assigned from the results of hybrid selected translation analysis in which small subfragments of the cDNA clones were used. These subfragments were derived from the 3' ends of the cDNA and did not cross hybridise between the different types of cDNA. Hybridisation of α-Amy1 and α-Amy2 cDNA probes to restriction enzyme digests of wheat nuclear DNA revealed that these are multigene families located on the group 6 (α-Amy1) and group 7 (α-Amy2) chromosomes. Studies on the levels of α-Amy1 and α-Amy2 mRNA in developing grain and in aleurone tissue indicated that the differences in isozyme expression are due to the patterns of mRNA accumulation. In aleurone tissue the α-Amy1 transcripts accumulate in parallel with other genes which are regulated by gibberellic acid, while the accumulation of α-Amy2 genes is sustained for 36 h longer.