A rice bZIP protein, designated OSBZ8, is rapidly induced by abscisic acid

A cDNA that encoded a bZIP protein, designated OSBZ8, was isolated from a rice embryo cDNA library by use of degenerate oligonucleotide probes that corresponded to the amino acid sequences conserved among the basic regions of plant G-box-binding factor-type bZIP proteins (GBF). OSBZ8 was shown to have structural features typical of the GBF-type bZIP proteins and to bind to G-box and G-box-like sequences that include ABA-responsive elements (ABREs) which have been functionally identified 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 imbibed mature rice embryos, of young plant tissues and of suspension-cultured cells. The accumulation of OSBZ8 mRNA in response to ABA preceded that of Osem and Rab16A mRNAs and was not inhibited by an inhibitor of protein synthesis, cycloheximide. By contrast, the induction of Osem 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 rice.