Apoptotic cell death in animals is regulated by cysteine proteinases called caspases. Recently, vacuolar processing enzyme (VPE) was identified as a plant caspase. VPE deficiency prevents cell death during hypersensitive response and cell death of limited cell layers at the early stage of embryogenesis. Because plants do not have macrophages, dying cells must degrade their materials by themselves. VPE plays an essential role in the regulation of the lytic system of plants during the processes of defense and development. VPE is localized in the vacuoles, unlike animal caspases, which are localized in the cytosol. Thus, plants might have evolved a regulated cellular suicide strategy that, unlike animal apoptosis, is mediated by VPE and the vacuoles.
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We thank Kenji Yamada for his valuable comments and discussion. Research in the authors’ laboratory was supported by the CREST project of the Japan Science and Technology Corporation, and grants-in-aid for scientific research (12138205 and 16085203) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.