DO PLANT CASPASES EXIST?
From a physiological perspective, any plant cell death-related protease could be named “plant caspase,” but this would not be in line with the definition used in animal research. Caspase nomenclature is based on the existence of Cys proteases with an absolute requirement for Asp at the P1 position and neither a specific function in cell metabolic processes (apoptosis) nor the presence of a specific tertiary structure (caspase-hemoglobinase fold) is required for classifying a protein as a caspase. Therefore, the question whether plant caspases exist relies on the existence in plants of Cys endoproteases that cleave adjacent an Asp residue. The available evidence strongly suggests that true caspase-like proteolytic activity is present in plants and, moreover, that this activity does play a pivotal role in plant PCD suggesting an evolutionary relationship. This view is based on the following observations: (a) the existence of cell death-related plant proteases that recognize and process s
