Expression of genes coding for sporamin and beta -amylase, the two most abu
ndant proteins in storage roots of sweet potato, is coordinately inducible
in atypical vegetative tissues by sugars. A sweet potato gene for beta -amy
lase (beta -Amy) with introns as well as a beta -Amy::GUS fusion gene compo
sed of the beta -Amy promoter and the GUS coding sequence, both showed suga
r-inducible expression in leaves of transgenic tobacco which occurred via a
hexokinase-independent pathway. Analyses using various 5'-terminal and int
ernal deletions of the beta -Amy promoter indicated that truncated promoter
s of beta -Amy containing a sequence between -901 and -820, relative to the
transcription start site, and the basic promoter region can confer sugar-i
nducible 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 eleme
nt in the truncated beta -Amy promoter abolished the sugar-inducible expres
sion, the results suggesting that the TGGACGG element plays an important ro
le in the coordinate induction of expression of genes for beta -amylase and
sporamin by sugars.