THE PROMOTER OF THE ARABIDOPSIS-THALIANA PLASTOCYANIN GENE CONTAINS AFAR UPSTREAM ENHANCER-LIKE ELEMENT INVOLVED IN CHLOROPLAST-DEPENDENT EXPRESSION

Plastocyanin is part of the photosynthetic electron transport chain in the chloroplast and is encoded in the nucleus. Expression of the Arab idopsis thaliana plastocyanin gene is organ specific: high mRNA levels are observed in young green parts of the plant. Furthermore, expressi on is dependent on the presence of light and functional chloroplasts. When grown in the presence of norflurazon under white light conditions , resulting in the photo-oxidative destruction of the chloroplast, pla stocyanin mRNA levels are strongly reduced. A -1579 to -9 promoter fra gment confers light-regulated and chloroplast-dependent expression to the beta-glucuronidase reporter gene in transgenic tobacco plants. Thi s suggests that regulation takes place at the level of transcription. A plastocyanin promoter deletion series ranging from -1579 to -121 whi ch was also tested in tobacco, revealed the presence of a strong posit ive regulating element (PRE) in the -1579 to -705 region. Deletion of this part of the promoter resulted in a almost-equal-to 100-fold reduc tion of GUS expression as measured in mature leaves. Surprisingly, thi s enhancer-like element was capable of stimulating transcription from a position downstream of its reporter. Moreover, it could also activat e a truncated CaMV 35S promoter. Dejetion of this element coincides wi th the loss of chloroplast-dependency of reporter gene expression, as judged by norflurazon treatment of transgenic seedlings. So, the activ ity of the PRE itself might depend on the presence of functional chlor oplasts.