Alfalfa Infection By an Incompatible Colletotrichum Induces Formation of Paramural Bodies and EV Secretion

We used serial block face SEM to compare subcellular changes in alfalfa cotyledons during infection by Colletotrichum destructivum (compatible) C. higginsianum (incompatible). Three-dimensional reconstruction revealed that alfalfa epidermal cells infected with C. destructivum undergo massive cytological changes, while incompatible species infection resulted in frequent formation of precursors of papilla-like structures. Incompatible interaction formed multivesicular body-like structures not seen in compatible interactions. These often fused with the host plasma membrane, forming paramural bodies that appeared to be releasing extracellular vesicles (EVs). Isolation of EVs from alfalfa leaves showed significantly more vesicles secretion from incompatible interaction compared to compatible infection.