Regulation of α-amylase-encoding gene expression in germinating seeds and cultured cells of rice

Abstract

Four α-amylase-encoding cDNA (α Amy-C) clones were isolated from a cDNA library derived from poly(A) +RNA of gibberellic acid (GA 3)-treated rice aleurone layers. Nucleotide sequence analysis indicates that the four cDNAs were derived from different α Amy genes. Expression of the individual α Amy gene in germinating seeds and cultured suspension cells of rice was studied using gene-specific probes. In germinating seeds, expression of the α Amy genes is positively regulated by GA 3 in a temporally coordinated but quantitatively distinct manner. In cultured suspension cells, in contrast, expression of the α Amy genes is negatively and differentially regulated by sugars present in the medium. In addition, one strong and one weak carbohydrate-starvation-responsive α Amy genes have been identified. Interactions between the promoter region (HS501) of a rice α Amy gene and GA3-inducible DNA binding proteins in rice aleurone cells were also studied. A DNA mobility-shift assay showed that the aleurone proteins interact with two specific DNA fragments within HS501. One fragment is located between nt −131 to −170 and contains two imperfect directly repeated pyrimidine elements and a putative GA 3-response element. The other fragment is located between nt −92 to −130 that contains a putative enhancer sequence. The interactions between aleurone proteins and these two fragments are sequence-specific and GA-responsive.