ANALYSIS OF THE GIBBERELLIN-RESPONSIVE PROMOTER OF A CATHEPSIN B-LIKE GENE FROM WHEAT

A wheat gene (A121) encoding a protein with sequence similarity to mammalian cathepsin B is regulated by gibberellic acid (GA) in aleurone layers of germinating grains. To analyse the mechanism of A121 regulation, its promoter was fused to the beta-glucuronidase reporter gene (GUS) and introduced by micro-projectile bombardment into aleurone layers of oat. With 2.3 kb of promoter sequence, the GUS expression was enhanced by GA treatment. This effect was reversed by abscisic acid (ABA). This result showed for A121, like the alpha-amylase genes, that the regulation by GA and ABA was at the level of transcription. The GA responsiveness of the promoter was retained with as little as 276 bp of promoter sequence. Sequence comparison with a GA responsive promoter of an alpha-amylase gene identified the conserved element GCAACGGCAACGATGG which is required intact for full expression of both promoters. However, there was no identifiable similarity in the cathepsin-like promoter with the GA-responsive element of alpha-amylase promoters with the consensus sequence TAACAAA, suggesting that GA affects more than one mechanism of transcriptional control.