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

Expression of genes coding for sporamin and beta -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 beta -amylase (beta -Amy) with introns as well as a beta -Amy::GUS fusion gene composed of the beta -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 beta -Amy promoter indicated that truncated promoters of beta -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 beta -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 beta -amylase and sporamin by sugars.