The Arabidopsis peptide kiss of death is an inducer of programmed cell death

Programmed cell death (PCD) has a key role in defence and development of all multicellular organisms. In plants, there is a large gap in our knowledge of the molecular machinery involved at the various stages of PCD, especially the early steps. Here, we identify kiss of death (KOD) encoding a 25-amino-acid peptide that activates a PCD pathway in Arabidopsis thaliana. Two mutant alleles of KOD exhibited a reduced PCD of the suspensor, a single file of cells that support embryo development, and a reduced PCD of root hairs after a 551C heat shock. KOD expression was found to be inducible by biotic and abiotic stresses. Furthermore, KOD expression was sufficient to cause death in leaves or seedlings and to activate caspaselike activities. In addition, KOD-induced PCD required light in leaves and was repressed by the PCD-suppressor genes AtBax inhibitor 1 and p35. KOD expression resulted in depolarization of the mitochondrial membrane, placing KOD above mitochondria dysfunction, an early step in plant PCD. A KODHGFP fusion, however, localized in the cytosol of cells and not mitochondria.