Figure 2.

Schematic representation of putative secretion pathways of pro-peptides and pro-enzymes.

Some precursors follow the conventional protein secretion pathway: the pro-enzyme/peptides are translocated into the ER, transported to the Golgi, and subsequently secreted into the extracellular space after fusion of the secretory vesicles with the plasma membrane. Other precursors can bypass the Golgi and follow the unconventional protein secretion pathway (left panel) to reach the apoplast. Exocyst-positive organelles (EXPOs) and multivesicular bodies (MVBs) appear to be particularly involved in this transport. Some precursors can be released in the apoplast after cell damage. Red, green, and blue arrows represent conventional protein secretion, unconventional protein secretion, and damage-induced protein release, respectively. Dashed arrows indicate paths that lack direct evidence. Blue dots represent peptide or protease precursors.