Role of a dual-targeted organellar RNA polymerase in controlling organelle function
Project Leader// Prof. Dr. Kristina Kühn
Graduate// Sarlita Dwiani
Institute of Biology
The discovery that the nucleus-encoded RNA polymerase RPOTmp is dually targeted to both mitochondria and plastids raised the question whether this enzyme may serve to co- ordinate metabolic functions in the two organelles. Answering this question will require to i) comprehensively determine transcriptional tasks of RPOTmp in mitochondria and plastids and ii) investigate how this enzyme’s activity and subcellular targeting are controlled. Our preliminary work has addressed the first of these points for plastids by performing a plastid genome- wide analysis of the promoters used and genes transcribed by RPOTmp. For this, we have adapted differential RNA sequencing (dRNA-Seq) and nascent transcript sequencing protocols for their application to plastids. Research planned in this project will extend this work to mitochondria: Next generation sequencing-based approaches will be employed to determine promoters used and genes transcribed by RPOTmp in mitochondria. Altogether, this work will lay open the potential of RPOTmp to modulate the expression of genes for photosynthesis and respiration. It will be complemented with investigations of the partitioning of RPOTmp between mitochondria and plastids. Using fusions with fluorescent reporter proteins, the accumulation of RPOTmp in either organelle under normal conditions and in response to specific mitochondrial or chloroplast stresses will be monitored using confocal laser scanning microscopy. This work will show if RPOTmp partitioning between mitochondria and plastids is regulated at the level of organellar import. Finally, we will scrutinise prior observations of stimulated mitochondrial transcription and overall stimulated mitochondrial biogenesis in plants that are impaired in mitochondrial energy conversion. We will investigate how the expression and activities of RPOTmp and of the mitochondrial-only RNA polymerase RPOTm respond to mitochondrial perturbations. This work will reveal how RPOTmp and RPOTm contribute to adjusting mitochondrial function according to the needs of the cell.