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Phage-Type RNA Polymerase RPOTmp Performs Gene-Specific Transcription in Mitochondria of Arabidopsis thaliana^[W],[OA]

^a Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley 6009 WA, Australia
^b Institut für Biologie/Genetik, Humboldt-Universität zu Berlin, 10115 Berlin, Germany
^c Centre for Computational Systems Biology, University of Western Australia, Crawley 6009 WA, Australia

¹ Address correspondence to kristina{at}cyllene.uwa.edu.au.

Transcription of mitochondrial genes in animals, fungi, and plants relies on the activity of T3/T7 phage-type RNA polymerases. 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 RNA polymerase in mitochondria of Arabidopsis thaliana. Examination of mitochondrial transcripts in rpoTmp mutants revealed major differences in transcript abundances between wild-type and rpoTmp plants. Decreased levels of specific transcripts were correlated with reduced abundances of the respiratory chain complexes I and IV. Altered transcript levels in rpoTmp were found to result from gene-specific transcriptional changes, establishing that RPOTmp functions in distinct transcriptional processes within mitochondria. Decreased transcription of specific genes in rpoTmp was not associated with changes in promoter utilization; therefore, RPOTmp function is not promoter specific but gene specific. This implies that additional gene-specific elements direct the transcription of a subset of mitochondrial genes by RPOTmp.