Expression of a higher-plant chloroplast psbD promoter in a cyanobacterium(Synechococcus sp strain PCC7942) reveals a conserved cis-element, designated PGT, that differentially interacts with sequence-specific binding factors during leaf development

The chloroplast psbD gene, which encodes the D2 subunit of photosystem II, is regulated by a blue light-responsive promoter (BLRP). We tested the abil ity of different regions of the barley (Hordeum vulagare) BLRP to drive tra nscription of the lacZ reporter gene in genomic transformants of Synechococ cus sp. strain PCC7942. The barley BLRP was transcribed in Synechococcus fr om the same initiation sites that are used in plant chloroplasts in vivo. A region of the BLRP, residing between -83 and -112 bp upstream from the tra nscription initiation sites, functioned as a negative element in Synechococ cus. Nucleotide sequences within this region are conserved among the psbD g enes of several monocots and dicots, and with the nuclear negative regulato ry element GT. Thus this new cis-element was designated Plastid GT, PGT. Pr oteins from chloroplasts of barley and Arabidopsis thaliana interacted with PGT in a sequence-specific and developmental-dependent manner. The DNA-pro tein complexes from Arabidopsis chloroplasts are composed of 60- and 38-kDa polypeptides. We postulate that GT and PGT have evolved in the nucleus and chloroplast, respectively, from a common ancestral regulatory element.