Sugar-responsible elements in the promoter of a gene for β-amylase of sweet potato

Expression of genes coding for sporamin and β-amylase, the two most abundant proteins in storage roots of sweet potato, is coordinately inducible in atypical vegetative tissues by sugars. A sweet potato gene for β-amylase (β-Amy) with introns as well as a β-Amy::GUS fusion gene composed of the β-Amy promoter and the GUS coding sequence, both showed sugar-inducible expression in leaves of transgenic tobacco which occurred via a hexokinase-independent pathway. Analyses using various 5′-terminal and internal deletions of the β-Amy promoter indicated that truncated promoters of β-Amy containing a sequence between −901 and −820, relative to the transcription start site, and the basic promoter region can confer sugar-inducible expression. This 82 bp region contained the TGGACGG sequence that plays an essential role in the sugar-inducible expression of the truncated promoter of the sporamin gene. Deletion or base substitutions of this element in the truncated β-Amy promoter abolished the sugar-inducible expression, the results suggesting that the TGGACGG element plays an important role in the coordinate induction of expression of genes for β-amylase and sporamin by sugars.