Exocytosis, Endocytosis and Membrane Recycling in Plant Cells

Abstract In plants, cell growth is dependent on vacuole enlargement, cell wall deposition and plasma membrane extension. Secretion (exocytosis) and uptake (endocytosis) of materials are two vital processes for cell function and cell–cell communication. The fusion of secretory vesicles with the plasma membrane (PM) during exocytosis is essential for proper cell function because it delivers proteins and lipids to the PM as well as proteins and polysaccharides to the cell wall. Basically, secretory proteins can be transported to the PM through the Golgi apparatus (conventional protein secretion) or bypassing the Golgi (unconventional protein secretion) via vesicle‐mediated pathways. In mature, nongrowing cells, the anterograde flow of materials is balanced by endocytosis, which retrieves excess membrane and recycles PM receptors and transporters. Clathrin‐mediated endocytosis (CME) and membrane microdomain‐associated endocytosis (MME) are the major well‐characterised routes. The balance of exocytosis and endocytosis is tightly regulated, which is crucial to both plant development and signalling processes. Key Concepts Conventional protein secretion (CPS) is the trafficking route for secretory proteins that are transported through the endoplasmic reticulum (ER), Golgi apparatus and (plasma membrane) PM via secretory vesicles. Unconventional protein secretion (UPS) is the process by which proteins are secreted by‐passing the Golgi apparatus. Endocytosis in plants shares conserved features with those in animals but also possesses some evolutionarily unique components. Clathrin‐mediated endocytosis (CME) and membrane microdomain‐associated endocytosis (MME) have been recognised to mediate the internalisation of cargo proteins. The balance of exocytosis and endocytosis regulates proteins and lipids in the PM and mediates signalling transduction and plant adaptation to an ever‐changing environment.