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(American Journal of Botany. 2008;95:1049-1062.) doi: 10.3732/ajb.2007404 © 2008 Botanical Society of America, Inc.

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KDEL-tailed cysteine endopeptidases involved in programmed cell death, intercalation of new cells, and dismantling of extensin scaffolds¹

² Technische Universität München, Lehrstuhl für Botanik, Biologikum-Weihenstephan, Am Hochanger 4, D-85350 Freising, Germany ³ Ohio University, Department of Chemistry and Biochemistry, Athens, Ohio 45701 USA ⁴ Max-Plank-Institut für Biochemie, Am Klopferspitz, D-82152 Martinsried, Germany

ABSTRACT

KDEL-tailed cysteine endopeptidases are a group of papain-type peptidases found in senescing tissue undergoing programmed cell death (PCD). Their genes have so far been cloned and analyzed in 12 angiosperms. They are synthesized as proenzymes with a C-terminal KDEL endoplasmatic reticulum retention signal, which is removed with the prosequence to activate enzyme activity. We previously identified three genes for KDEL-tailed cysteine endopeptidases (AtCEP1, AtCEP2, AtCEP3) in Arabidopsis thaliana. Transgenic plants of A. thaliana expressing β-glucuronidase (GUS) under the control of the promoters for the three genes were produced and analyzed histochemically. GUS activity was promoter- and tissue-specific GUS activity during seedling, flower, and root development, especially in tissues that collapse during final stages of PCD, and in the course of lateral root formation. KDEL-tailed cysteine endopeptidases are unique in being able to digest the extensins that form the basic scaffold for cell wall formation. The broad substrate specificity is due to the structure of the active site cleft of the KDEL-tailed cysteine endopeptidase that accepts a wide variety of amino acids, including proline and glycosylated hydroxyproline of the hydroxyproline rich glycoproteins of the cell wall.

Key Words: Arabidopsis thaliana • Brassicaceae • cell wall degradation • development in generative and vegetative tissues • Euphorbiaceae • β-glucuronidase (GUS) • KDEL-tailed cysteine endopeptidases • programmed cell death • ricinosome • Ricinus communis

Received for publication 10 December 2007. Accepted for publication 10 June 2008.

FOOTNOTES

¹ The authors thank H. Cochran (Washington State University, USA) for artwork, J. S. Greenwood (University of Guelph, Canada) for valuable discussions, and D. Simpson (Denmark) for critically reading the manuscript. This work was supported by the Deutsche Forschungsgemeinschaft (Gi154/11-5).

⁵ Present address: Max-Plank-Institut für Entwicklungsbiologie, Spemannstr. 37-39, D-72076 Tübingen, Germany

⁶ Author for correspondence (e-mail: christine.gietl{at}wzw.tum.de)

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