Proposed mechanism for regulation of H₂ O₂ -induced programmed cell death in plants by binding of cytochrome c to 14-3-3 proteins

Programmed cell death (PCD) is crucial for development and homeostasis of all multicellular organisms. In human cells, the double role of extra-mitochondrial cytochrome c in triggering apoptosis and inhibiting survival pathways is well reported. In plants, however, the specific role of cytochrome c upon release from the mitochondria remains in part veiled yet death stimuli do trigger cytochrome c translocation as well. Here, we identify an Arabidopsis thaliana 14-3-3ι isoform as a cytosolic cytochrome c target and inhibitor of caspase-like activity. This finding establishes the 14-3-3ι protein as a relevant factor at the onset of plant H₂ O₂ -induced PCD. The in vivo and in vitro studies herein reported reveal that the interaction between cytochrome c and 14-3-3ι exhibits noticeable similarities with the complex formed by their human orthologues. Further analysis of the heterologous complexes between human and plant cytochrome c with plant 14-3-3ι and human 14-3-3ε isoforms corroborated common features. These results suggest that cytochrome c blocks p14-3-3ι so as to inhibit caspase-like proteases, which in turn promote cell death upon H₂ O₂ treatment. Besides establishing common biochemical features between human and plant PCD, this work sheds light onto the signaling networks of plant cell death.