A VPE family supporting various vacuolar functions in plants

Vacuolar processing enzyme (VPE) is a cysteine protease that has substrate specificity toward Asn and Asp residues, and found in various eukaryotic organisms including higher plants and mammals. Plant VPEs are separated into three subfamilies: seed‐type, vegetative‐type and uncharacterized‐type. VPE was originally identified as a protease responsible for the maturation of seed storage proteins, and recent research has shown that it is a key protease responsible for the maturation of various vacuolar proteins not only in maturating cotyledons, but also in vegetative tissues. Thus, the VPE‐mediated processing system is important for various vacuolar functions in the plant. Vegetative‐type VPEs are expressed during senescence or pathogen‐induced hypersensitive response. A VPE‐deficiency abolished programmed cell death during hypersensitive response in tobacco leaves after TMV infection. This suggests that vegetative‐type VPEs are involved in vacuolar‐organized programmed cell death.