Transient Gene Expression as a Tool to Monitor and Manipulate the Levels of Acidic Phospholipids in Plant Cells.

Anionic phospholipids represent only minor fraction of cell membranes lipids but they are critically important for many membrane-related processes, including membrane identity, charge, shape, the generation of second messengers, and the recruitment of peripheral proteins. The main anionic phospholipids of the plasma membrane are phosphoinositides phosphatidylinositol 4-phosphate (PI4P), phosphatidylinositol 4,5-bisphosphate (PI4,5P2), phosphatidylserine (PS), and phosphatidic acid (PA). Recent insights in the understanding of the nature of protein-phospholipid interactions enabled the design of genetically encoded fluorescent molecular probes that can interact with various phospholipids in a specific manner allowing their imaging in live cells. Here, we describe the use of transiently transformed plant cells to study phospholipid-dependent membrane recruitment.

A Combinatorial Lipid Code Shapes the Electrostatic Landscape of Plant Endomembranes.

Membrane surface charge is critical for the transient, yet specific recruitment of proteins with polybasic regions to certain organelles. In eukaryotes, the plasma membrane (PM) is the most electronegative compartment of the cell, which specifies its identity. As such, membrane electrostatics is a central parameter in signaling, intracellular trafficking, and polarity. Here, we explore which are the lipids that control membrane electrostatics using plants as a model. We show that phosphatidylinositol-4-phosphate (PI4P), phosphatidic acidic (PA), and phosphatidylserine (PS) are separately required to generate the electrostatic signature of the plant PM. In addition, we reveal the existence of an electrostatic territory that is organized as a gradient along the endocytic pathway and is controlled by PS/PI4P combination. Altogether, we propose that combinatorial lipid composition of the cytosolic leaflet of organelles not only defines the electrostatic territory but also distinguishes different functional compartments within this territory by specifying their varying surface charges.

Precision targeting by phosphoinositides: how PIs direct endomembrane trafficking in plants.

Each phosphoinositide (PI, also known as phosphatidylinositol phosphate, polyphosphoinositide, PtdInsP or PIP) species is partitioned in the endomembrane system and thereby contributes to the identity of membrane compartments. However, membranes are in constant flux within this system, which raises the questions of how the spatiotemporal pattern of phosphoinositides is established and maintained within the cell. Here, we review the general mechanisms by which phosphoinositides and membrane trafficking feedbacks on each other to regulate cellular patterning. We then use the specific examples of polarized trafficking, endosomal sorting and vacuolar biogenesis to illustrate these general concepts.