As every year, we received many great projects, reflecting the excellence and creativity of the SPS LabEx research teams. These 3 new projects, added to those selected during the past years, increase to 16 the number of projects funded through this call.

Here are the 2016 laureates:

EpiRepair: “Relationship between DNA repair and small RNA-induced epigenetic silencing” (post-doc supervised by Hervé Vaucheret, IJPB)
RNA interference (RNAi) is an epigenetic defense mechanism activated when RNA quality control (RQC) processes are deficient or saturated by an excess of aberrant RNAs. Whereas RQC destroys only aberrant RNAs in cells where they are produced, RNAi destroys both functional and aberrant RNAs in a systemic manner, due to the involvement of mobile small RNAs, which makes it more dangerous than RQC. How are aberrant RNAs produced and why the propensity to undergo RNAi varies from gene to gene remain to be understood. We reasoned that the answers to these two questions could have to do with the frequency at which DNA breaks and DNA repair occur at a given locus. In this project, we will determine if DNA damages induced by genotoxic agents or CRISPR-mediated DNA breaks provoke the production of aberrant RNAs that trigger RNAi. We will also explore if mutations in the DNA repair machinery favor or prevent the production of aberrant RNAs. Finally, we will define to which extent CRISPR-mediated homologous recombination reduces RNAi risk compared with classical transformation. We anticipate that this project will shed light on the nature and origin of the RNA molecules that activate RNAi. An expected outcome of this project is also to design transgenes or CRISPR substrates that are not prone to RNAi.

MITRA: “Functional characterization of the Mitochondrial Translation apparatus in higher plants” (post-doc supervised by Hakim Mireau, IJPB)
Mitochondria are the site of aerobic respiration but they also specify cytoplasmic male sterility in plants. These organelles have retained a genome of limited coding capacity and whose expression relies almost entirely on nuclear-encoded protein factors. Over the last years, the discovery of Pentatricopeptide Repeat (PPR) proteins has allowed to make significant progresses in understanding some aspects of gene expression in plant mitochondria but mitochondrial translation, the last level of mRNA expression that is also the least prone to easy molecular analyses, has remained largely unexplored. It is nevertheless clear that, despite of its prokaryotic origin, mitochondrial translation machineries differ from their bacterial counterparts in many mechanical aspects. This project aims at better understanding the molecular functioning of the mitochondrial translation apparatus and takes large advantage of the ribosome profiling technology that gives a faithful measure on the translational level of mRNAs and on the positions occupied by translating ribosomes at the nucleotide level. We will first make a general description of key mechanical aspects of the mitochondrial translation apparatus and better understand its role in the phenotypic plasticity of plants. We will then characterize two PPR proteins specifically involved in the control of mitochondrial translation. One facilitates the translation of an essential mitochondrial transcript in Arabidopsis thaliana and the second corresponds to a restorer of fertility gene that inhibits specifically the translation of its cognate CMS-inducing transcript in Brassica napus.

SWEELEM: “Impact on the xylem development of sugar transport modification in a model plant species” (PhD supervised by Rozenn Le Hir, IJPB)
During the development of the floral stem, the xylem tissue (fibers and vessels) requires important amount of sugars in order to sustain the formation of the secondary cell wall. However, the mechanisms by which sugars are transported to their site of use are far from being understood. In this project, we aim at deciphering the role of sugar transporters from the SWEET family in the formation of the vascular system in the model species Arabidopsis thaliana. Based on previous results obtained in the group, we will assess the role of these transporters by a genetic approach and the characterization of mutant lines impaired in the expression of four members of the family. We will focus our study on the analysis of the xylem development in the floral stem in long-day growth conditions. We also showed that the sweet11sweet12 double mutant line is more tolerant to freezing conditions, most probably because of an accumulation of sugar. Thus, the effect of multiple mutations in SWEET genes will be further evaluated in abiotic stress conditions, such as cold or drought stress, which are known to impact the sugar metabolism. Moreover, in order to better characterize the function of the SWEET proteins, their affinity for the cell wall polysaccharides precursors will be assessed by a biochemistry approach. The results obtained during this PhD should allow to better understand the role of the SWEET proteins during the xylem development and the formation of its secondary cell wall.

SWEELEM will be the final PhD project attributed via this call. Indeed, only postdoc projects will be funded in 2017, which will be the last edition of the SPS Research Open Call.