Phage-Type RNA Polymerase RPOTmp Performs Gene-Specific Transcription in Mitochondria of Arabidopsis thaliana

Transcription of mitochondrial genes in animals, fungi, and plants relies on the activity of T3/T7 phage-type RNApolymerases. Two such enzymes, RPOTm and RPOTmp, are present in the mitochondria of eudicotyledonous plants;RPOTmp is additionally found in plastids. We have characterized the transcriptional role of the dual-targeted RNApolymerase in mitochondria of Arabidopsis thaliana. Examination of mitochondrial transcripts in rpoTmp mutants revealedmajor differences in transcript abundances between wild-type and rpoTmp plants. Decreased levels of specific transcriptswere correlated with reduced abundances of the respiratory chain complexes I and IV. Altered transcript levels in rpoTmpwere found to result from gene-specific transcriptional changes, establishing that RPOTmp functions in distinct transcriptionalprocesses within mitochondria. Decreased transcription of specific genes in rpoTmp was not associated withchanges in promoter utilization; therefore, RPOTmp function is not promoter specific but gene specific. This implies thatadditional gene-specific elements direct the transcription of a subset of mitochondrial genes by RPOTmp.