The function of plant metacaspases, identified by limited sequence homology to the animal caspases that control cell death, has remained elusive. Coll et al. have now elucidated the actions of two metacaspases in the small plant Arabidopsis. One metacaspase, AtMC1, promoted cell death, and the other, AtMC2, acted antagonistically to stall cell death. The results help to elucidate the mechanisms by which plants control cell survival during development and defend against pathogen attack.