The spinach AtpC and AtpD genes contain elements for light-regulated, plastid-dependent and organ-specific expression in the vicinity of the transcription start sites

Run-on assays with isolated nuclei demonstrate that the transcription rates of AtpC and AtpD (gene products: the CF1 subunits gamma and delta of the chloroplast ATP synthase) are comparable in spinach seedlings. However, chimeric GUS gene fusions with 5'-flanking regions of the AtpC gene direct an approximately 10-fold lower GUS level in transgenic tobacco compared with equivalent fragments from the AtpD gene. Both promoters contain sequences in the vicinity of the respective TATA boxes, which are sufficient to direct light-regulated, plastid-dependent and organ-specific expression of the GUS gene. In contrast, the upstream regions of both promoters differ: the higher GUS level directed by the AtpD promoter is caused by enhancer-like elements located upstream of the region involved in the regulated expression, while nucleotides upstream of -73 in the AtpC promoter contribute relatively little to the promoter activity. 5'-Deletion analyses and site-directed mutagenesis studies indicated that the -73/-48 bp AtpC region contains cis-elements crucial for this regulated expression. If five nucleotides within this region (-59/-55) are exchanged, the GUS gene is constitutively expressed and the activity in etiolated seedlings, in seedlings with photobleached plastids and in roots increases to the level detectable in green cotyledons. It is concluded that signal transduction pathways from different regulators converge prior to gene regulation and that these five nucleotides are part of a cis-element which functions as a repressor in darkness, in tissues with impaired plastids and in roots.