Programmed Cell Death in Plants: Apoptotic but Not Quite

Abstract

Plants have evolved distinct pathways and strategies from those of animals to cope with environmental stresses as well as microbial invaders. This is in part due to the sessile nature of plants as well as their particular mode of cellular organization and architecture. Whereas apoptosis in animals is a common mechanism for the clearance of unwanted cells by neighboring cells or circulating macrophages, the presence of a rigid cell wall in plants precludes this cellular cleansing strategy, and instead other mechanisms more akin to autophagic cell death would be required to remove undesirable cells. In spite of the apparent importance of programmed cell death (PCD) in plants, a molecular description of the key executioners and their control pathways remains elusive. Nevertheless, some of the common cytological changes that have been observed between plant PCD and animal apoptosis suggest that the underlying strategies for dismantling eukaryotic cells may have evolved before the divergence of these two kingdoms. Recent studies on the involvement of various proteases and the highly conserved Bax inhibitor-1 protein in control of plant PCD are consistent with this notion, and their further study should reveal novel insights on the cell death engine in plants.