Characterization of cis-Acting Elements in Light Regulation of the Nuclear Gene Encoding the A Subunit of Chloroplast

We have characterized cis-acting elements involved in light regulation of the nuclear gene (GapA) encoding the A subunit of chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in Arabidopsis thaliana. Our results show that a 1.1-kb promoter fragment of the GapA gene is sufficient to confer light inducibility and organ specificity in transgenic Nicotiana tabacum (tobacco) plants, using the 0-glucuronidase gene of Escherichia coli as the reporter gene. Deletion analysis indicates that the-359 to- 110 bp region of the GapA gene is necessary for light responsiveness. Within this region there are three copies of a decamer repeat (termed the Gap box) having the consensus sequence 5'-CAAATGAA(AIG)A-3', which has not been charac-terized in the promoter regions of other light-regulated genes. A deletion (to-247) producing loss of one copy of these elements from the GapA promoter reduces light induction by two- to threefold compared with a promoter deletion (to-359) with all three Gap boxes present, while deletion of all three Gap boxes (to-110) abolishes light induction completely. Gel mobility shift experiments using tobacco nuclei as the source of nuclear proteins show that GapA promoter fragments that contain these repeats bind strongly to a factor in the nuclear extract and that binding can be abolished by synthetic competitors consisting only of a monomer or dimer of the Gap box. Furthermore, a trimer, dimer, and monomer of the Gap box show binding activity and, like the authentic GapA promoter-derived probes, show binding activities that are correlated with Gap box cop