Autophagy mechanism and alternative pathways for autophagosomes in plants. (a) Following an upstream stimulus, such as starvation, double membrane vesicles, autophagosomes, appear and engulf portions of cytosol, long-lived proteins, and organelles such as mitochondria. Autophagosomes eventually fuse with lysosomes, endosomes, or vacuole. Autophagosomes are degraded together with their cargo and the building blocks are pumped back into the cytosol for reuse. (b) Autophagosomes may fuse directly with the vacuole (observed in A. thaliana) (c) or, may first fuse with “lysosome-like structure” or endosomes to form “autolysosome-like structures” and then, eventually may fuse with the vacuole (observed in tobacco plant).
