Hormonal regulation of a cysteine proteinase gene, EPB-1, in barley aleurone layers: cis- and trans-acting elements involved in the co-ordinated geneexpression regulated by gibberellins and abscisic acid

The synthesis of EPB, a cysteine proteinase responsible for the degradation of seed endosperm storage proteins in barley (Hordeum vulgare), is induced by gibberellins (GA) and repressed by abscisic acid (ABA). The EPB gene fa mily consists of two very similar members, EPB-1 and EPB-2, with the former being more highly induced by GA. We have functionally characterized the ci s-acting elements in the EPB-1 promoter and determined that a gibberellin r esponse element (GARE), a pyrimidine box and an upstream element are necess ary for GA induction. By comparison with the promoters of alpha-amylase gen es, which are also induced by GA, we suggest that GARE is coupled with the upstream element and the pyrimidine box to form a GA response complex. In a ddition, we have shown that the 3'-untranslated/untranscribed region of the EPB-1 gene is required for a low background expression in the absence of G A. Constitutive expression of a transcription factor, GAMyb, in the absence of GA leads to the transactivation of EPB-1 expression in a dosage depende nt manner with the highest level comparable to that in fully GA-induced tis sue. Go-expression of a truncated version of GAMyb containing only the DNA binding domain blocks the GA-induction of EPB-1, further supporting the rol e of GAMyb in the regulation of gene expression. Although ABA is very effec tive in blocking the GA induction of EPB-1, it has no effect on the GAMyb-m ediated expression of EPB-1. We suggest that ABA acts upstream of the forma tion of functional GAMyb which co-ordinates the hormonal regulation of a di verse group of genes in cereal aleurone layers, including those encoding EP B and a-amylases.