Interaction of a gibberellin-induced factor with the upstream region of an alpha-amylase gene in rice aleurone tissue.

The interaction between the DNA sequences of an alpha-amylase (EC 3.2.1.1) gene and a tissue-specific factor induced in rice (Oryza sativa L.) aleurone tissue by gibberellin was studied. DNA mobility-shift during electrophoresis indicated that a 500-base-pair sequence (HS500) of a rice alpha-amylase genomic clone (OSamy-a) specifically interacted with a factor from gibberellin-induced rice aleurone tissue. The amount of complex formed between the HS500 DNA fragment and the gibberellin-induced factor increased in proportion to increasing amounts of aleurone extract and decreased with the addition of unlabeled HS500 DNA fragment. A specific segment of the HS500 fragment was protected from exonuclease III digestion by protein(s) in the aleurone extract, revealing the approximate position of the protein-DNA interaction. In the protected region, there is a direct repeat that overlaps with a potential stem-loop structure. Protein in extracts from leaves, roots, or deembryonated seeds incubated without gibberellin A3 did not bind to the HS500 DNA fragment. However, the binding factor was induced in deembryonated seeds when exogenous gibberellin A3 was added during seed imbibition. This suggests that activation of alpha-amylase synthesis by gibberellin may be mediated by the formation of a factor that interacts with a specific sequence of the alpha-amylase gene.