Developmental stage-specific multi-subunit plastid RNA polymerases (PEP) in wheat

Most photosystem I and II plastid genes are transcribed by a plastid encode d Escherichia coil-like RNA polymerase (PEP). In this study, we show that b oth promoter selectivity and light-dependency of PEP change dramatically du ring development in wheat leaves. In the leaf tip, psbA and psbD promoter a ctivities are light induced, whilst psbC, psbE and 16S rRNA promoters do no t function efficiently irrespective of light conditions. In contrast to the leaf tip, in the basal portion all PEP promoters studied function in the d ark as well as the light, except for psbD. Using in vitro transcription, we found that PEP in the illuminated leaf tip can initiate transcription from the -35 destructed psbA promoter, but the -35 element is essential for tra nscription in the basal portion. There is an extended -10 element in the ps bA promoter, recognized by the PEP in the illuminated leaf tip or purified sigma(70)-type Escherichia coil RNA polymerase but not by the PEP in the le af base. These results suggest that during wheat leaf development, PEP in t he leaf base that is functional for most PEP promoters even in the dark is replaced by the light-dependent PEP selectively transcribing the psbA and p sbD promoters.