Structure and Blue - Light - Responsive Transcription of a Chloroplast psbD Promoter from Arabidopsis thaliana ’ Paul

We characterized the effects of light on psbD transcription and mRNA levels during chloroplast development in Arabidopsis thaliana. After 6 to 12 hours of illumination of dark-grown seedlings, two psbD mRNAs were detected and their 5’ ends were mapped to positions -550 and -190 bp upstream from the psbD translational start codon. Their kinetics of accumulation resembled the accumulation of chloroplast psbA and rbcL mRNAs but differed from the accumulation of the nuclear-encoded Lhcb and Chs mRNAs. A third psbD mRNA with its 5’ end at position -950 accumulated after illumination of >180 h. The 5‘ ends of this transcript were mapped to a nucleotide sequence that is highly conserved with functional sequences in the barley (Hordeum vulgare) blue-light-responsive promoter (BLRP). Transcription from the Arabidopsis psbD promoter was 3-fold higher in blue relative to red light, whereas red and blue light affected total chloroplast, rbcL, and 16s rDNA transcription similarly. This study shows that transcription of Arabidopsis psbD i s mediated by a BLRP and suggests that psbD genes in other land plants are regulated by a common blue-light-signaling pathway. lsolating the BLRP from Arabidopsis will allow molecular genetic studies aimed at identifying the pertinent photoreceptor and components of this phototransduction pathway.