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First published online March 10, 2006; 10.1104/pp.105.073841 Plant Physiology 141:47-60 (2006) © 2006 American Society of Plant Biologists Identification and Characterization of a Stress-Inducible and a Constitutive Small Heat-Shock Protein Targeted to the Matrix of Plant Peroxisomes1,[W]Albrecht-von-Haller-Institute for Plant Sciences, Department of Plant Biochemistry, Georg-August-University Goettingen, D–37077 Goettingen, Germany (C.M., L.B., S.R.); Department of Chemistry, Technical University Munich, D–85747 Garching, Germany (M.H.); and Max-Planck-Institute of Experimental Medicine, Proteomics Group, D–37075 Goettingen, Germany (O.J.)
Small heat-shock proteins (sHsps) are widespread molecular chaperones for which a peroxisomal localization has not yet been reported. The Arabidopsis (Arabidopsis thaliana) genome encodes two sHsps with putative peroxisomal targeting signals type 1 or 2 (PTS1 or PTS2). As demonstrated by double-labeling experiments using full-length fusion proteins with enhanced yellow fluorescent protein and deletion constructs lacking the putative targeting domains, AtHsp15.7 (At5g37670) and AtAcd31.2 (At1g06460) are targeted to the peroxisome matrix by a functional PTS1 (SKL>) and a functional PTS2 (RLx5HF), respectively. The peroxisomal localization of AtAcd31.2 was further confirmed by isolation of leaf peroxisomes from Arabidopsis by two successive sucrose density gradients, protein separation by one- and two-dimensional gel electrophoresis, and mass spectrometric protein identification. When AtHsp15.7 and AtAcd31.2 were heterologously expressed in yeast (Saccharomyces cerevisiae) and directed to the cytosol by deletion of the PTSs, both sHsps were able to complement the morphological phenotype of yeast mutants deficient in the cytosolic homologs ScHsp42 or ScHsp26. According to expression studies by reverse transcription-PCR, AtAcd31.2 is constitutively expressed, whereas AtHsp15.7 is hardly expressed under normal conditions but strongly induced by heat and oxidative stress, the latter of which was triggered by the catalase inhibitor 3-aminotriazole or the herbicide methyl viologen applied by watering of whole plants or infiltration of rosette leaves. Thus, plants are exceptional among eukaryotes in employing sHsps in the peroxisome matrix to prevent unspecific aggregation of partially denatured proteins under both physiological and stress conditions.
1 This work was supported by the Deutsche Forschungsgemeinschaft (grant no. RE1304/2 to S.R.), by Fonds der Chemischen Industrie (to M.H.), and by the government of Lower Saxony (a Dorothea-Erxleben stipend to S.R.). 2 Present address: Department of Plant Pathology, Faculty of Agriculture, Shizuoka University, Shizuoka 422–8529, Japan. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Sigrun Reumann (sreuman{at}gwdg.de). [W] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.073841. * Corresponding author; e-mail sreuman{at}gwdg.de; fax 49–551–395749. Received November 5, 2005; returned for revision February 12, 2006; accepted February 16, 2006. This article has been cited by other articles:
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