Characterization of the Light-Responsive Promoter of Rice Chloroplast psbD-C Operon and the Sequence-Specific DNA Binding Factor

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Abstract
The transcription of rice plastid psbD-psbC genes encoding photosystem II reaction center protein D2 and chlorophyll α-binding protein CP43 is closely regulated by light. To elucidate the sequence requirement for the light-responsive promoter of psbD-psbC operon, transcriptional analysis of the rice promoter was performed with deleted mutants and site-directed mutants in vitro. Deletion of –546˜– 100 upstream sequences resulted in 4- to 5- fold decrease in the transcription rate. Further deletion of –99˜–40 conserved region of repeated sequences resulted in 2-fold decrease in the transcription rate. The core light-responsive promoter requires “–10” element but not “–35” element for accurate initiation of basal transcription. No downstream promoter element was found in the +4˜+111 region. The competitive gel-retardation experiments revealed the presence of DNA-binding protein in the rice chloroplasts, which interacts specifically with the –60˜–37 repeated sequences. Southwestern blot analysis further demonstrated that the binding factor is composed of 36-kDa polypeptide(s).

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