Negative Regulation in the Expression of a Sugar-Inducible Gene in Arabidopsis thaliana (A Recessive Mutation Causing Enhanced Expression of a Gene for β-Amylase)

Abstract Expression of a β-amylase gene of Arabidopsis thaliana (ATβ-Amy)is regulated by sugars. We identified a mutant, hba1, in which the level of expression of ATβ-Amy in leaves of plants that had been grown in a medium with 2% sucrose was significantly higher than that in wild-type plants. Higher than wild-type levels of β-amylase in hba1 plants depended on the presence of 1 to 2% sucrose or 1% glucose in the medium, whereas leaves of mutant plants grown with higher levels of sugars had β-amylase activities similar to those in leaves of wild-type plants. The hba1 phenotype was recessive and did not affect levels of sugars and starch in leaves. It is proposed that expression of ATβ-Amy is regulated by a combination of both positive and negative factors, dependent on the level of sugars, and that HBA1 might function to maintain low-level expression of ATβ-Amy until the level of sugars reaches some high level. Results of crosses of hba1 plants with transgenic plants that harbored an ATβ-Amy:GUS transgene with 1587 bp of the 5[prime]-upstream region suggested that HBA1 affects expression of ATβ-Amy in trans. The hba1 plants also had growth defects and elevated levels of anthocyanin in their petioles. However, sugar-regulated changes in levels of several mRNAs other than β-amylase mRNA were unaffected in hba1 plants, suggesting that only a subset of sugar-regulated genes is under the control of HBA1.