Intercellular communication is critical for multicellularity. It coordinates the activities within individual cells to support the function of an organism as a whole. Plants have developed remarkable cellular machines –the plasmodesmata (PD) pores- which interconnect every single cell within the plant body, establishing direct membrane and cytoplasmic continuity, a situation unique to plants. PD’s are indispensable for plant life. They control the flux of molecules between cells and are decisive for development, environmental adaptation and defense against viruses for example. However, how PD’s integrate signalling to coordinate responses at a multicellular level remains unclear.

A striking feature of PD organisation, setting them apart from animal cell junctions, is a strand of endoplasmic reticulum (ER) running through the pore, tethered extremely tight (~10nm) to the plasma membrane (PM) by unidentified “spokes”. To date, the function of ER-PM contacts at PD remains a complete enigma. We propose here a pioneer project based on very recent data, to explore the function of organelle tethering for intercellular signalling by three interconnected workpackages that will feed each other to build up a cohesive program research by 1) Identifying the mechanisms of membrane-tethering at the atomic/molecular level by combining biophysical assays and molecular dynamics modelling; 2) Elucidating the dynamics and architecture of ER-PM contact sites at PD using cutting edge electron tomography (ET) and cryo-electron microscopy (cryo-EM); 3) Uncovering the function of ER-PM apposition for plant intercellular communication using plant genetics and cell biology.

This CDR project funded by FRS-FNRS is carried out in tight collaboration with the Team of Dr Emmanuelle Bayer, recently granted by an ERC funding (Laboratoire de Biogénèse Membranaire, University of Bordeaux, France). Jules Petit, a PhD student is involved in this project.