Proposed mechanism for regulation of H2O2‐induced programmed cell death in plants by binding of cytochrome c to 14‐3‐3 proteins

SUMMARY 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 H2O2‐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 H2O2 treatment. Besides establishing common biochemical features between human and plant PCD, this work sheds light onto the signaling networks of plant cell death. Significance Statement Common features of the cytochrome c‐dependent pathways leading to programmed cell death in plants and humans are herein revealed. In response to oxidative stress, cytochrome c is released from mitochondria to the cytoplasm to hamper the iota isoform of the 14‐3‐3 protein family, thereby decreasing the inhibition of caspase‐like activity and likely contributing to promote cell death in plants.