The GCN4 motif in a rice glutelin gene is essential for endosperm-specific gene expression and is activated by Opaque-2 in transgenic rice plants.
The GCN4 motif is conserved in a number of seed storage protein genes, and promoter fragments containing this motif have been shown to be involved in controlling seed-specific expression of the genes studied. All genes encoding the rice seed storage protein glutelin contain the GCN4 motif at similar sites in their 5' flanking regions. Using a stable homologous transgenic system, we have analysed the promoter of the rice glutelin gene GluB-1 and demonstrated that the GCN4 motif functions as an essential cis-element for endosperm-specific gene expression. Moreover, a 21 bp GluB-1 promoter fragment spanning the GCN4 motif, as a multimer, directed GUS gene expression in endosperm of transgenic rice plants, when fused directly to the core promoter (-46) of CaMV 35S. In transiently transfected rice protoplasts, over a hundred-fold transactivation was observed from the 21 bp sequence by the bZIP type transcriptional activator Opaque-2 (O2) co-expressed under a CaMV 35S promoter. The transactivation was also evident in transgenic plants containing both O2 and the 21 bp sequence/GUS fusion. The O2-mediated activation requires binding of O2 to an intact GCN4 motif. Our results suggest that a bZIP protein functionally similar to O2 may exist in rice and participate in controlling the endosperm-specific expression of GluB-1 through the GCN4 motif.
Department of Biotechnology, National Institute of Agrobiological Resources, Ibaraki, Japan.
C Y
CY
Wu
A
A
Suzuki
H
H
Washida
F
F
Takaiwa
D019677:Artificial Gene Fusion; D001483:Base Sequence; D017124:Conserved Sequence; D018744:DNA, Plant / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D017930:Genes, Reporter; D005966:Glucuronidase / Q000235:genetics; D005983:Glutens / Q000235:genetics*; D006651:Histocytochemistry; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation
D018744:DNA, Plant; D004268:DNA-Binding Proteins; D010940:Plant Proteins; D014157:Transcription Factors; C067402:opaque-2 protein, Zea mays; D005983:Glutens; D005966:Glucuronidase