Research project: Role of OMP24 in the regulation of mitochondria-chloroplasts MCSs and lipid trafficking in response to phosphate starvation in Arabidopsis thaliana
Supervisor: Dr. Morgane Michaud
Lab: LPCV (Cell & Plant Physiology Laboratory), LIPID team
Year: 2021-2022

Abiotic stresses such as cold, high light, and nutrient starvation induce lipid remodeling in plants as acclimation response. Phosphate (Pi) starvation drives a huge alteration of membrane composition since about 1/3 of the cellular Pi is used to synthetize phospholipids. Lipid trafficking and membrane biogenesis are complex processes that takes place throughout vesicular and non-vesicular transport. Knowing how membrane biogenesis works and how it is regulated would help to increase stress resistance in crops and therefore their production rate. Lipid trafficking between mitochondria and chloroplasts is essentially mediated only by non-vesicular transport at membrane contact sites (MCSs). MCSs are dynamic structures that keep two organelles’ membranes in a proximity between 10-30 nm without fusion of the membranes, facilitating the exchange of lipids which are thought to be channeled through an apolar microenvironment. In certain MCSs that form at mitochondria-chloroplast interface, have been identified the Mitochondria Transmembrane Lipoprotein (MTL) supercomplex which is involved in the regulation of lipid trafficking during phosphate starvation. The MTL complex counts about 200 proteins, most of them being located in mitochondrial membranes. Interestingly, an uncharacterized protein of the chloroplast envelope, Outer Membrane Protein24 (OMP24), was also identified in the MTL complex, suggesting it could play a role in chloroplast-mitochondria communication during Pi starvation. During my thesis, I have mainly used biochemical approaches to shade some light about the role of OMP24 in the formation of mitochondria-chloroplast MCSs and in the regulation of lipid trafficking in Pi starvation. Results suggest that OMP24 is a Pi-responsive gene that plays an important role by tethering the two organelle’s membranes probably interacting with mitochondrial proteins that remain to be confirmed. Moreover, overexpression of OMP24 alters the general and mitochondrial lipid homeostasis and remodeling in Pi deficiency. These results highlight the importance of this protein in plant lipid homeostasis and open important perspectives in the understanding of the mechanisms involved in chloroplast-mitochondria communication during Pi starvation.

Matteo will pursue a PhD with Prof. Roman Ulm at UNIGE Université de Genève.