Programmed cell death in C. elegans, mammals and plants

Programmed cell death (PCD) is the regulated removal of cells within an organism and plays a fundamental role in growth and development in nearly all eukaryotes. In animals, the model organism Caenorhabditis elegans (C. elegans) has aided in elucidating many of the pathways involved in the cell death process. Various analogous PCD processes can also be found within mammalian PCD systems, including vertebrate limb development. Plants and animals also appear to share hallmarks of PCD, both on the cellular and molecular level. Cellular events visualized during plant PCD resemble those seen in animals including: nuclear condensation, DNA fragmentation, cytoplasmic condensation, and plasma membrane shrinkage. Recently the molecular mechanisms involved in plant PCD have begun to be elucidated. Although few regulatory proteins have been identified as conserved across all eukaryotes, molecular features such as the participation of caspase-like proteases, Bcl-2-like family members and mitochondrial proteins appear to be conserved between plant and animal systems. Transgenic expression of mammalian and C. elegans pro- and anti-apoptotic genes in plants has been observed to dramatically influence the regulatory pathways of plant PCD. Although these genes often show little to no sequence similarity they can frequently act as functional substitutes for one another, thus suggesting that action may be more important than sequence resemblance. Here we present a summary of these findings, focusing on the similarities, between mammals, C. elegans, and plants. An emphasis will be placed on the mitochondria and its role in the cell death pathway within each organism. Through the comparison of these systems on both a cellular and molecular level we can begin to better understand PCD in plant systems, and perhaps shed light on the pathways, which are controlling the process. This manuscript adds to the field of PCD in plant systems by profiling apoptotic factors, to scale on a protein level, and also by filling in gaps detailing plant apoptotic factors not yet amalgamated within the literature.