| Summary: | Caspases are key regulators of apoptosis in animals. This correlation has driven plant researchers for decades to look for caspases regulating PCD in plants. These studies revealed caspase-like activities, caspase-related proteases and other Cys proteases regulating PCD in plants, but no caspases, and no conserved death pathway as in apoptosis. Here, we critically review the evidence for Cys proteases implicated in cell death in plants. We discuss the role of papain-like Cys proteases, vacuolar processing enzymes and metacaspases in PCD during development of tracheary elements, seed coat, suspensor, tapetum and during the hypersensitive response. There are several convincing cases where these Cys proteases are required for PCD, but this requirement seems often not conserved across different plant species and there are also cases where Cys proteases contribute to PCD without being essential, or have other roles than regulating PCD. These data illustrate the need for caution generalizing the role of Cys proteases regulating PCD in plants, and calls for studies on other PCD regulators and other roles of plant Cys proteases.
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