Non-vesicular glycerolipids transport in plant cells

International audienceIn Eukaryotic cells, organelles are delineated by one or several membranes that are composed of a specific assembly of lipids and proteins ensuring the identity of each cell compartment and regulating their biogenesis and function. Lipids regulate many aspects of cell biology including vesicular trafficking, protein targeting, programmed cell death or signaling. They also play key roles in response to stress, which is particularly important for organisms such as plants that constantly cope with a multitude of environmental variations. Membranes are mainly composed of glycerolipids, sterols and sphingolipids. Lipid precursors are primarily synthesized in plastids and in the endoplasmic reticulum. Then, they have to be specifically directed to other cell compartments where they can be modified and transported to other organelles to regulate membrane biogenesis and function. Thus, lipid transfer is a key process involved in the maintenance of membrane homeostasis, in particular in stress conditions. Lipid exchanges between organelles can rely on vesicular or non-vesicular transport. Whereas vesicular transport concerns mainly organelles connected to the endomembrane system, such as the Golgi, vacuoles or the plasma membrane, non-vesicular lipid trafficking concerns virtually all organelles. This lipid transfer mechanism is thought to occur at membrane contact sites, corresponding to specific cell structures formed by the close apposition of two membranes at a distance <= 30nm. In this chapter, we will summarize our current knowledge about the mechanisms involved in non-vesicular lipid transport in plant cells, with a particular focus on glycerolipids, the main components of organelle membranes