Figure 3.

The proposed models for the biogenesis and secretion of extracellular vesicles in plant cells and in Gram-negative bacteria. (A) In plant cells, the trans-Golgi network plays a similar function as the early endosome in mammalian cells. (B) In Gram-negative bacteria, the outer membrane is an asymmetrical bilayer membranous structure with lipopolysaccharide in the outer leaflet and phospholipids in the inner leaflet. The phospholipid layer possesses different molecular packing manners and triggers the budding of the outer membrane (① and ②). Finally, the budding of the outer membrane is enclosed and released as outer-membrane vesicles (③).