Abstract
The chloroplast genome is transcribed by plastid-encoded (PEP) and nucleus-encoded (NEP) RNA polymerases. PEP is a cyanobacterial-type, multisubunit enzyme whose activity is regulated by sigma-like transcription initiation factors that are nucleus-encoded. In general, chloroplast photosynthesis-related genes are transcribed by a PEP enzyme and non-photosynthesis genes are transcribed by NEP enzymes. Is this scenario true to lower plants, like mosses? We have recently demonstrated the loss of rpoA gene from the moss Physcomitrella patens chloroplast genome, and we have isolated and characterized the nuclear rpoA gene encoding a subunit of PEP enzyme. The nuclear encoded RpoA protein was observed in the chloroplasts of moss protonemata cells. This indicates that chloroplast PEP enzyme is encoded separately by chloroplast and nuclear genomes in the moss. These data provide new insights into the regulation and evolution of chloroplast transcription.
