Organellar gene expression

Team OGE / Etienne Delannoy

Our main focus is to understand the regulation of gene expression in organelles.

In parallel, the OGE team develops functional genomics tools available for the plant community.

Understanding plant organellar functions and regulations, which are at the core of the plant metabolism, is a major challenge towards improving crops with better yields and a better adaptability to a fluctuating environment. The organelles, plastids and mitochondria, are the main places of energy metabolism of eukaryotic cells, but they also play a key role in many metabolic pathways. Throughout evolution and after the ancestral events of endosymbiosis at their origins, organelles have lost much of their original genomes by the transfer of genetic material to the nucleus. As a consequence, the organelle metabolism requires many proteins encoded by the nucleus and targeted to the organelles. However, they have retained small genomes encoding key proteins and RNAs necessary for their biology creating a requirement for coordinate regulation of nuclear and organellar gene expression. A wide range of organellar transcriptional and post-transcriptional processes including DNA replication, RNA transcription, RNA processing, RNA editing, RNA splicing and translation rely on nuclear encoded proteins. Among these nuclear factors, the large family of pentatricopeptide repeat proteins (PPR), which is currently the main object of study of the team, is a key component of the regulation of these two organellar genomes. These nuclear encoded proteins are almost exclusively targeted to mitochondria and/or chloroplasts where they bind to specific RNAs and are involved in all steps of gene expression from transcription to translation.

Roles for PPR proteins in organellar gene expression: from transcription (1) to translation (5). (2) RNA cleavage, (3) splicing, (4) editing. “]

The team was involved in the discovery of the PPR family in 2000, in the genomic characterization of the family in Arabidopsis, rice and Physcomitrella and in several genetic and functional characterizations of members of the Arabidopsis family. We are now focusing on the study of organellar gene expression in a dynamic context i.e. during development or stress conditions through 3 main projects:

RNA editing and regulation of photosynthesis complexes during development and stresses.

Organelles at the core of plant responses to pathogens.

Organelles and early development - function of organellar genome expression factors.

The OGE team has been also involved in an international project of Arabidopsis Interactome Mapping coordinated by Pr Joseph Ecker (Salk Institute, San Diego) and Pr Marc Vidal (DFCI, Boston). This plant protein interactome network map was generated using the improved Y2H assay developed at DFCI for C. elegans, human and yeast proteins. The first data set from this project was published in 2011 (AIM, 2011) where a proteome-wide binary protein-protein interaction map containing about 6200 high quality interactions between about 2700 proteins was described.