A RICE BZIP PROTEIN, DESIGNATED OSBZ8, IS RAPIDLY INDUCED BY ABSCISIC-ACID

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.