Structural organization and differential expression of rice alpha-amylase genes

Rice alpha-amylases are encoded by a multigene family that has previously been classified into 5 hybridization groups. DNA sequence and Southern blot analysis identified three genes (RAmy1A, RAmy1B and RAmy1C) in Group 1 with DNA sequence identity of at least 90%. Hybridization Group 2 is represented by only one gene, RAmy3D, which is identical to a previously characterized cDNA, pOS137. RAmy3D is physically linked to the sole representative of Group 5, RAmy3E. The identity between these two genes is 81.4% in the coding region but less than 50% in the 5' and 3' flanking regions. Northern blot analysis and RNA-PCR were used to detect the expression of alpha-amylase genes in various tissues. Alpha-amylase mRNA was abundant in germinating seeds and callus. Some genes were also expressed at much lower levels in roots, young leaves and immature seeds. RAmy1A and RAmy3E were expressed in all tissues while RAmy3D was expressed in all tissues except the immature seeds. RAmy1B was weakly expressed only in callus. RAmy1A transcript was most abundant in the germinating seeds, while RAmy3D and RAmy3E transcripts were most abundant in callus and immature seeds, respectively.