Ultraviolet-C Overexposure Induces Programmed Cell Death in Arabidopsis, Which Is Mediated by Caspase-like Activities and Which Can Be Suppressed by Caspase Inhibitors, p35 and Defender against Apoptotic Death

International audience; Plants, animals, and several branches of unicellular eukaryotes use programmed cell death (PCD) for defense or developmental mechanisms. This argues for a common ancestral apoptotic system in eukaryotes. However, at the molecular level, very few regulatory proteins or protein domains have been identified as conserved across all eukaryotic PCD forms. A very important goal is to determine which molecular components may be used in the execution of PCD in plants, which have been conserved during evolution, and which are plant-specific. Using Arabidopsis thaliana, we have shown that UV radiation can induce apoptosis-like changes at the cellular level and that a UV experimental system is relevant to the study of PCD in plants. We report here that UV induction of PCD required light and that a protease cleaving the caspase substrate Asp-Glu-Val-Asp (DEVDase activity) was induced within 30 min and peaked at 1 h. This DEVDase appears to be related to animal caspases at the biochemical level, being insensitive to broad-range cysteine protease inhibitors. In addition, caspase-1 and caspase-3 inhibitors and the pan-caspase inhibitor p35 were able to suppress DNA fragmentation and cell death. These results suggest that a YVADase activity and an inducible DEVDase activity possibly mediate DNA fragmentation during plant PCD induced by UV overexposure. We also report that At-DAD1 and At-DAD2, the two A. thaliana homologs of Defender against Apoptotic Death-1, could suppress the onset of DNA fragmentation in A. thaliana, supporting an involvement of the endoplasmic reticulum in this form of the plant PCD pathway.