Identification of Dof proteins with implication in the gibberellin-regulated expression of a peptidase gene following the germination of rice grains

Type III carboxypeptidase (CPD3) is one of the hydrolytic enzymes whose exp ression is up-regulated by gibberellins (GA) in the aleurones. of germinate d cereal grains. A number of pyrimidine boxes and a sequence resembling the gibberellic acid response element (GARE) are observed in the region upstre am of the transcription initiation site of the CPD3 gene, showing a charact eristic of cereal GA-responsive genes. Transient gene expression assays in germinated rice aleurone demonstrated that the CPD3 promoter was able to co nfer hormonally responses on the expression of the reporter gene. By southw estern screening, several cDNAs encoding the Dof class proteins were isolat ed from a rice aleurone library. Each mRNA accumulation for five novel memb ers of Dof proteins (OsDof1-5) occurs with a different time course and in a tissue-specific manner following the germination of grains. Of these, the expression of the OsDof3 gene is abundant in aleurones where it precedes th at of the CPD3 gene, implying that this is an early response gene of GA. Th e OsDof3 protein, expressed in Escherichia coli, selectively bound AAAG mot ifs of the pyrimidine boxes through the DNA-binding activity of its Dof dom ain. Co-expression experiments in aleurones suggested that the OsDof3 prote in should play a regulatory role in the expression of the CPD3 gene under t he control of CIA. (C) 2001 Elsevier Science B.V. All rights reserved.