title: Activation of the programmed cell death pathway by inhibition of proteasome function in plants.
abstract: Proteasomes constitute the major machinery to degrade or process proteins by ATP/ubiquitin-mediated proteolysis. Recent findings suggest a pivotal role of the ubiquitin/proteasome pathway in the regulation of apoptosis in animal cells. Here we show that virus-induced gene silencing of two different subunits of the 26 S proteasome, the alpha 6 subunit of the 20 S proteasome and RPN9 subunit of 19 S regulatory complex, both activated the programmed cell death (PCD) program, accompanied by reduced proteasome activity and accumulation of polyubiquitinated proteins. These results demonstrate that disruption of proteasome function leads to PCD in plant cells. The affected cells showed morphological markers of PCD, including nuclear condensation and DNA fragmentation, accompanied by the 10-fold higher production of reactive oxygen species and increased ion leakage for 3-fold. Similar to apoptosis in animal system, mitochondrial membrane potential was decreased, cytochrome c released from mitochondria to cytosol, and caspase 9- and caspase 3-like proteolytic activities detected in the cells. Interestingly, this proteasome-mediated PCD stimulated the expression of only a subset of transcripts that are highly induced during pathogen-mediated hypersensitive response cell death, indicating that the two PCD pathways are differentially regulated. Taken together, these results provide the first direct evidence that proteasomes play a role in the regulatory program of PCD in plants. Controlled inhibition of proteasome activities may be involved in developmentally or environmentally activated plant cell death programs.
authors.affiliation: Laboratory of Plant Genomics, Korea Research Institute of Bioscience and Biotechnology, P. O. Box 115, Yusong, Taejon 305-600, Korea.
authors.forename: Moonil
authors.initials: M
authors.lastname: Kim
authors.forename: Joon-Woo
authors.initials: JW
authors.lastname: Ahn
authors.forename: Un-Ho
authors.initials: UH
authors.lastname: Jin
authors.forename: Doil
authors.initials: D
authors.lastname: Choi
authors.forename: Kyung-Hee
authors.initials: KH
authors.lastname: Paek
authors.forename: Hyun-Sook
authors.initials: HS
authors.lastname: Pai
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000502:physiology*; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D053938:DNA Fragmentation; D020868:Gene Silencing; D005822:Genetic Vectors; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials; D008928:Mitochondria / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D059828:Plant Cells; D010944:Plants / Q000201:enzymology*; D046988:Proteasome Endopeptidase Complex; D012333:RNA, Messenger / Q000032:analysis; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014026:Nicotiana / Q000201:enzymology / Q000821:virology; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D025801:Ubiquitin; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex