Classification and characterization of the rice ?-amylase multigene family

Abstract

To establish the size and organization of the rice α-amylase multigene family, we have isolated 30 α-amylase clones from three independent genomic libraries. Partial characterization of these clones indicates that they fall into 5 hybridization groups containing a total of 10 genes. Two clones belonging to the Group 3 hybridization class have more than one gene per cloned fragment. The nucleotide sequence of one clone from Group 1, λOSg2, was determined and compared to other known cereal α-amylase sequences revealing that λOSg2 is the genomic analog of the rice cDNA clone, pOS103. The rice α-amylase genes in Group 1 are analogous to the α-Amy1 genes in barley and wheat. λOSg2 contains sequence motifs common to most actively transcribed genes in plants. Two consensus sequences, TAACA _G ^A A and TATCCAT, were found in the 5′ flanking regions of α-amylase genes of rice, barley and wheat. The former sequence may be specific to α-amylase gene while the latter sequence may be related to a ‘CATC’ box found in many plant genes. Another sequence called the pyrimidine box ( _T ^C CTTTT _T ^C ) was found in the α-amylase genes as well as other genes regulated by gibberellic acid (GA). Comparisons based on amino acid sequence alignment revealed that the multigene families in rice, barley and wheat shared a common ancestor which contained three introns. Some of the descendants of the progenitor α-amylase gene appear to have lost the middle intron while others maintain all three introns.