Programmed cell death, mitochondria and the plant hypersensitive response

Abstract

The plant response to attempted infection by microbial pathogens is often accompanied by rapid cell death in and around the initial infection site, a reaction known as the hypersensitive response. This response is associated with restricted pathogen growth and represents a form of programmed cell death (PCD). Recent pharmacological and molecular studies have provided functional evidence for the conservation of some of the basic regulatory mechanisms underlying the response to pathogens and the activation of PCD in animal and plant systems. In animals, the mitochondrion integrates diverse cellular stress signals and initiates the death execution pathway, and studies indicate a similar involvement for mitochondria in regulating PCD in plants. But many of the cell-death regulators that have been characterized in humans, worms and flies are absent from the Arabidopsis genome, indicating that plants probably use other regulators to control this process.

Autophagic Components Contribute to Hypersensitive Cell Death in Arabidopsis

“…The best described form of PCD in animals is apoptosis, but plants apparently lack apoptotic regulatory genes including cysteine proteases called caspases (Lam et al, 2001). Nonetheless, caspase-like activities have been detected during HR and diseaserelated cell death which could be assigned to different types of proteases (Woltering, 2004;Vercammen et al, 2007).…”

Caspases: an ancient cellular sword of Damocles

“…For example, paracaspases from humans, zebrafish and C. elegans are predicted to contain death domains (DD), a homotypic protein-protein interaction module found in many molecules involved in metazoan apoptosis, 9 and some metacaspase genes in Arabidopsis appear to contain an Nterminal Zn-Pro domain, a motif also found in LSD-1, a protein known to be involved in PCD in plants. 13 The functional characterization of the metacaspases and paracaspases is still in its early stages and at present it is not clear even whether some or all of these proteins possess protease activity. For example, the human paracaspase did not cause apoptosis or undergo autoprocessing (a hallmark of caspase activation) when transfected in human cells, even when artificially oligomerized.…”

“…A similar pathway in plants, termed the hypersensitive response, may also employ caspase-like proteins for an innate immune function. 13 Therefore, it is possible that the nonapoptotic, immune functions of caspaselike enzymes are at least as evolutionarily ancient as their apoptosis-associated activities. Further investigations of the nonapoptotic functions of ced-3 will prove interesting and may shed light on this possibility.…”

Defense induced by a bis-aryl methanone compound leads to resistance in potato against Phytophthora infestans

“…Another feature of disease resistance in many plants is the rapid collapse and death of challenged cells in the HR, a form of programmed cell death (PCD) in plants (Dangl et al 1996;Lam et al 2001). Hypersensitive cell death depends on O 2 H 2 O 2 involvement is also reported in many types of PCD induced by abiotic stress.…”