Sequences upstream of the YRTA core region are essential for transcription of the tobacco atpB NEP promoter in chloroplasts in vivo

Abstract

Transcription of the plastid atpB gene is accomplished by plastid-encoded (PEP) and nuclear-encoded (NEP) RNA polymerases. In contrast to NEP promoters of many other plastid genes, the tobacco atpB NEP promoter exhibits robust activity in chloroplasts in vivo. Previously, in vitro transcription assays using extracts from non-photosynthetic cells identified two elements required for full atpB NEP promoter activity, a core sequence and an upstream GAA box. Of these, only the core sequence containing the motif YRTA is conserved in the majority of NEP promoters. We used plastid transformation to examine the requirements for atpB NEP promoter activity in chloroplasts. Our results demonstrate that sequences upstream of the core element are essential for promoter activity in vivo, and that transcription of the NEP promoter in chloroplasts is not dependent on activity from an overlapping PEP promoter.