A cDNA that encoded a bZIP protein, designated OSBZ8, was isolated fro
m a rice embryo cDNA library by use of degenerate oligonucleotide prob
es that corresponded to the amino acid sequences conserved among the b
asic regions of plant G-box-binding factor-type bZIP proteins (GBF). O
SBZ8 was shown to have structural features typical of the GBF-type bZI
P proteins and to bind to G-box and G-box-like sequences that include
ABA-responsive elements (ABREs) which have been functionally identifie
d in the promoters of ABA-inducible genes, such as Em, Osem and Rab16.
The accumulation of OSBZ8 mRNA was induced by treatment with ABA of i
mbibed mature rice embryos, of young plant tissues and of suspension-c
ultured cells. The accumulation of OSBZ8 mRNA in response to ABA prece
ded that of Osem and Rab16A mRNAs and was not inhibited by an inhibito
r of protein synthesis, cycloheximide. By contrast, the induction of O
sem and Rab16A was partially inhibited and almost completely inhibited
, respectively, by cycloheximide. These results strongly suggest that
OSBZ8 might be involved in the regulation of transcription by ABA in r
ice.