IDENTIFICATION OF A LIGHT-RESPONSIVE REGION OF THE NUCLEAR GENE ENCODING THE B-SUBUNIT OF CHLOROPLAST GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE FROM ARABIDOPSIS-THALIANA

We report here the identification of a cis-acting region involved in l ight regulation of the nuclear gene (GapB) encoding the B subunit of c hloroplast glyceraldehyde 3-phosphate dehydrogenase from Arabidopsis t haliana. Our results show that a 664-bp GapB promoter fragment is suff icient to confer light induction and organ-specific expression of the Escherichia coli B-glucuronidase reporter gene (Gus) in transgenic tob acco (Nicotiana tabacum) plants. Deletion analysis indicates that the -261 to -173 upstream region of the GapB gene is essential for light i nduction. This region contains four direct repeats with the consensus sequence 5'-ATGAA(A/G)A-3' (Gap boxes). Deletion of all four repeats a bolishes light induction completely. In addition, we have linked a 109 -bp (-263 to -152) GapB upstream fragment containing the four direct r epeats in two orientations to the -92 to +6 upstream sequence of the c auliflower mosaic virus 35S basal promoter. The resulting chimeric pro moters are able to center light induction and to enhance leaf-specific expression of the Gus reporter gene in transgenic tobacco plants. Bas ed on these results we conclude that Cap boxes are essential for light regulation and organ-specific expression of the GapB gene in A. thali ana. Using gel mobility shift assays we have also identified a nuclear factor from tobacco that interacts with GapA and GapB DNA fragments c ontaining these Cap boxes. Competition assays indicate that Cap boxes are the binding sites for this factor. Although this binding activity is present in nuclear extracts from leaves and roots of light-grown or dark-treated tobacco plants, the activity is less abundant in nuclear extracts prepared from leaves of dark-treated plants or from roots of greenhouse-grown plants. In addition, our data show that this binding factor is distinct from the GT-1 factor, which binds to Box II and Bo x III within the light-responsive element of the RbcS-3A gene of pea.