Agenda de l'ENS de Lyon

Role of phosphatidylinositol-4-phosphate in the formation and function of membrane contact sites in Arabidopsis thaliana

ven 08 déc 2023



Soutenance de thèse de monsieur DUBOIS Gwennogan. Sous la direction de monsieur JAILLAIS Yvon

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Description générale

During my thesis, I explored the function of an anionic lipid, phosphatidylinositol 4-phosphate (PI4P), in Arabidopsis thaliana. I focused on the function of SUPPRESSOR OF ACTIN7 (SAC7), a PI4P phosphatase. I found that SAC7 plays a pivotal role in regulating tissue-specific PI4P levels in root. I showed that SAC7 localizes in the cortical endoplasmic reticulum (ER), in close proximity with the plasma membrane (PM). ER/PM contact sites are maintained thanks to the action of tethering proteins that are embedded in the ER and contact the PM through lipid binding. I showed that in plants, PI4P plays a critical role in the establishment of ER/PM contacts via its interaction with two families of tethering proteins, the SYNAPTOTAGMINs (SYT) and MULTIPLE C2 DOMAINS PROTEIN (MCTPs). In a first study, I showed that SAC7 controls the density and dynamics of SYT1-mediated ER/PM contacts. Furthermore, through its tissue-specific expression, SAC7 contributes to shape very different ER morphologies in the different cell types of the root epidermis. In a second study, I discovered SAC7's involvement in plasmodesmata biology. Plasmodesmata are membrane lined channels that are unconventional ER/PM contact sites. These structures create cytoplasmic sleeves between neighboring cells, enabling cell-to-cell diffusion of developmental regulators. I found that SAC7 regulates MCTP stabilization at plasmodesmata, likely affecting ER/PM tethering in these structures. As such, SAC7 affects cytosolic diffusion in a tissue specific manner. Together, my work and a companion study from the Bayer lab, propose that the strength of MCTP/PI4P interaction controls the ER/PM apposition in plasmodesmata and thus the opening or closing of the cytoplasmic sleeve. This mode of regulation is independent of the well-known plasmodesmata regulator callose and provides a new paradigm involving membrane contact sites in the regulation of intercellular communication.


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