Selective Activation of the psb A and psb D Promoters in Matured Wheat Chloroplasts

Chloroplast genes of higher plants are transcribed by at least two types of plastid RNA polymerases, eubacterial RNA polymerase of which core subunits (α, β, β′ and β″)are encoded by the plastid genome (plastid-encoded RNA polymerase; PEP) and phage type nuclear encoded RNA polymerases (NEP). PEP promoters are reminiscent of the E. coli σ70 promoters with -35 and -10 consensus elements that are spaced 17–19 bases apart. Photosynthesis genes have been shown to be transcribed by PEP[1]. Transcription from most of PEP promoters increases during chloroplast development and declines after chloroplast maturation[2]. Exceptions are the promoters for the psbA and psbD genes encoding PSII reaction center proteins (D1 and D2, respectively) which turn over rapidly in a light-dependent manner[3]. Transcriptions of both genes were maintained highly active in the developed wheat chloroplasts under illumination[4], suggesting presence of gene specific mechanism to activate these promoters.