Philippe Giegé

The biological questions that have interested me since the beginning of my research career have mainly concerned gene expression and its specificities in plant mitochondria, a fascinating compartment of eukaryote cells, that uniquely combines prokaryote-like processes with features that appeared during eukaryote evolution. During my PhD, in the laboratory of Axel Brennicke in Berlin and Ulm, I was able to perform the first gene expression analysis at the whole transcriptome level of a plant mitochondria, i.e. by determining the full extent of RNA editing activity. As a post-doctoral researcher, in Oxford, with C.J. Leaver, I broadened the scope of this research by focusing on the coordination of gene expression between mitochondria and the nucleus in Arabidopsis. This led to my recruitment at CNRS in 2003. Since 2008, I have established my research team in Strasbourg and resumed the study of mitochondrial gene expression by becoming a specialist of pentatricopeptide repeat (PPR) proteins, some of the major players in post-transcriptional processes recently discovered at this time, which are 80 times more abundant in plants than in animals. The study of these proteins has been the main object of research carried out in my team in the past ten years. In particular, a major contribution has been to identify PPR proteins involved in RNase P activity, consisting in the 5’ maturation of tRNAs. These proteins that we called PRORP for "proteinaceous RNase P" are localized in both organelles and the nucleus and perform the endonucleolytic activity defining RNase P. We have determined that these proteins have completely replaced ribonucleoproteins (RNP) for RNase P activity in plants. Biophysical studies of PRORP / tRNA complexes suggest that PRORP proteins are structural mimics of RNP RNase P. This work answered the long-standing question on the nature of RNase P enzymes in plants and was a change of paradigm because it was previously accepted that RNase P activity would be universally carried by catalytic RNAs vestiges of the putative prebiotic RNA world. More recently, my team has focused on mitochondrial translation, revealing that the plant mitochondrial ribosome is unique both in terms of structure and of protein content, with numerous PPR proteins occurring as core ribosomal proteins.