Final Report Summary - APPL (Anionic PhosPhoLipids in plant receptor kinase signaling)
Many signaling proteins permanently or transiently localize to specific organelles for function. It is well established that certain lipids act as biochemical landmarks to specify compartment identity. However, they also influence membrane biophysical properties, which emerge as important features in specifying cellular territories. Such parameters include the membrane inner surface potential, which varies according to the lipid composition of each organelle. In particular, anionic phospholipids, which are minor lipids in biological membranes, are critical to establish membrane electrostatic properties as well as defining docking platforms on the surface of cellular compartments. Using plants as a research model, we are tackling the following questions:
i) Where are anionic phospholipids localized in the cell and by which mechanisms?
ii) What are the functions of these anionic phospholipids in controlling membrane identity and organization?
iii) How anionic phospholipids contribute to receptor signalling to regulate plant development?
We found that the plant plasma membrane (PM) and the cell plate of dividing cells have a unique electrostatic signature controlled by phosphatidylinositol-4-phosphate (PI4P) (Simon, Platre et al., 2016 Nature Plants). Our results further revealed that, contrarily to other eukaryotes, PI4P massively accumulates at the PM, establishing it as a critical hallmark of this membrane in plants. Membrane surface charges control the PM localization and function of the polar auxin transport regulator PINOID, as well as proteins from the BRI1 KINASE INHIBITOR1 (BKI1)/MEMBRANE ASSOCIATED KINASE REGULATORs (MAKRs) family, which are involved in brassinosteroid and receptor-like kinase signaling. We anticipate that this PI4P-driven physical membrane property will control the localization and function of many proteins involved in development, reproduction, immunity and nutrition. We also showed that each plasma membrane-derived compartments have a distinct electrostatic signature, set up by a combinatorial code of anionic phospholipids, including PI4P, phosphatidylserine (PS) and phosphatidic acid (Platre et al., 2018 Dev Cell). This ‘‘electrostatic code’’ may represent a fundamental patterning principle of the endomembrane system and be a key determinant in protein targeting. Finally, using super-resolution microscopy, we showed that PS forms nanoplatforms of about 50nm at the plasma membrane (Platre et al., 2019 Science). These domains are involved in the lateral segregation of signaling proteins (such as Rho GTPases) upon their activation. Using a PS-deficient mutant, we demonstrated that PS-dependent partitioning of Rho GTPases at the plasma membrane is essential to downstream signaling.
i) Where are anionic phospholipids localized in the cell and by which mechanisms?
ii) What are the functions of these anionic phospholipids in controlling membrane identity and organization?
iii) How anionic phospholipids contribute to receptor signalling to regulate plant development?
We found that the plant plasma membrane (PM) and the cell plate of dividing cells have a unique electrostatic signature controlled by phosphatidylinositol-4-phosphate (PI4P) (Simon, Platre et al., 2016 Nature Plants). Our results further revealed that, contrarily to other eukaryotes, PI4P massively accumulates at the PM, establishing it as a critical hallmark of this membrane in plants. Membrane surface charges control the PM localization and function of the polar auxin transport regulator PINOID, as well as proteins from the BRI1 KINASE INHIBITOR1 (BKI1)/MEMBRANE ASSOCIATED KINASE REGULATORs (MAKRs) family, which are involved in brassinosteroid and receptor-like kinase signaling. We anticipate that this PI4P-driven physical membrane property will control the localization and function of many proteins involved in development, reproduction, immunity and nutrition. We also showed that each plasma membrane-derived compartments have a distinct electrostatic signature, set up by a combinatorial code of anionic phospholipids, including PI4P, phosphatidylserine (PS) and phosphatidic acid (Platre et al., 2018 Dev Cell). This ‘‘electrostatic code’’ may represent a fundamental patterning principle of the endomembrane system and be a key determinant in protein targeting. Finally, using super-resolution microscopy, we showed that PS forms nanoplatforms of about 50nm at the plasma membrane (Platre et al., 2019 Science). These domains are involved in the lateral segregation of signaling proteins (such as Rho GTPases) upon their activation. Using a PS-deficient mutant, we demonstrated that PS-dependent partitioning of Rho GTPases at the plasma membrane is essential to downstream signaling.