Caspase-like protease involvement in the control of plant cell death

Cell death as a highly regulated process has now been recognized to be an i mportant, if not essential, pathway that is ubiquitous in all multicellular eukaryotes. In addition to playing key roles in the morphogenesis and scul pting of the organs to give rise to highly specialized forms and shapes, ce ll death also participates in the programmed creation of specialized cell t ypes for essential functions such as the selection of B cells in the immune system of mammals and the formation of tracheids in the xylem of vascular plants. Studies of apoptosis, the most well-characterized form of animal pr ogrammed cell death, have culminated in the identification of a central tri partite death switch the enzymatic component of which is a conserved family of cysteine proteases called caspases. Studies in invertebrates and other animal models suggest that caspases are conserved regulators of apoptotic c ell death in all metazoans. In plant systems, the identities of the main ex ecutioners that orchestrate cell death remain elusive. Recent evidence from inhibitor studies and biochemical approaches suggests that caspase-like pr oteases may also be involved in cell death control in higher plants. Furthe rmore, the mitochondrion and reactive oxygen species may well constitute a common pathway for cell death activation in both animal and plant cells. Cl oning of plant caspase-like proteases and elucidation of the mechanisms thr ough which mitochondria may regulate cell death in both systems should shed light on the evolution of cell death control in eukaryotes and may help to identify essential components that are highly conserved in eukaryotes.