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J. Biol. Chem., Vol. 283, Issue 2, 774-783, January 11, 2008

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Metacaspase-8 Modulates Programmed Cell Death Induced by Ultraviolet Light and H₂O₂ in Arabidopsis^*

Rui He¹, Georgina E. Drury², Vitalie I. Rotari, Anna Gordon, Martin Willer, Tabasum Farzaneh, Ernst J. Woltering, and Patrick Gallois³

From the Faculty of Life Sciences, University of Manchester, 3.614 Stopford Building, Oxford Road, Manchester M13 9PT, United Kingdom and the Agrotechnology and Food Sciences Group, Wageningen University and Research Centre, 6700 AA Wageningen, The Netherlands

Programmed cell death (PCD) is a genetically controlled cell death that is regulated during development and activated in response to environmental stresses or pathogen infection. The degree of conservation of PCD across kingdoms and phylum is not yet clear; however, whereas caspases are proteases that act as key components of animal apoptosis, plants have no orthologous caspase sequences in their genomes. The discovery of plant and fungi metacaspases as proteases most closely related to animal caspases led to the hypothesis that metacaspases are the functional homologues of animal caspases in these organisms. Arabidopsis thaliana has nine metacaspase genes, and so far it is unknown which members of the family if any are involved in the regulation of PCD. We show here that metacaspase-8 (AtMC8) is a member of the gene family strongly up-regulated by oxidative stresses caused by UVC, H₂O₂, or methyl viologen. This up-regulation was dependent of RCD1, a mediator of the oxidative stress response. Recombinant metacaspase-8 cleaved after arginine, had a pH optimum of 8, and complemented the H₂O₂ no-death phenotype of a yeast metacaspase knock-out. Overexpressing AtMC8 up-regulated PCD induced by UVC or H₂O₂, and knocking out AtMC8 reduced cell death triggered by UVC and H₂O₂ in protoplasts. Knock-out seeds and seedlings had an increased tolerance to the herbicide methyl viologen. We suggest that metacaspase-8 is part of an evolutionary conserved PCD pathway activated by oxidative stress.

Received for publication, May 21, 2007 , and in revised form, November 12, 2007.

^* This work was supported in part by a Biotechnology and Biological Sciences Research Council, Swindon, United Kingdom, research grant. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Present address: College of Chinese Materia Medica, Guangzhou University of Chinese Medicine, Guangzhou, 510405, China.

² Recipient of a Biotechnology and Biological Sciences Research Council studentship.

³ To whom correspondence should be addressed. Tel.: 44-161-275-3922; Fax:44-161-275-3938; E-mail: patrick.gallois{at}manchester.ac.uk.

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