Plant and Cell Physiology Advance Access published online on April 23, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn065
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Functional characterization of Arabidopsis Calreticulin1a: a key alleviator of endoplasmic reticulum stress
1 Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-22100 Lund, Sweden
2 Department of Cell and Organism Biology, Biology Building, Lund University, Sölvegatan 35, SE-223 62 Lund, Sweden
3 Max-Planck-Institute of Molecular Plant Physiology, Am Muehlenberg 1, DE-14476 Potsdam, Germany
4 Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G2H7, Canada
5 Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, SE-90187, Umeå, Sweden
*Corresponding author: Dr. Staffan Persson. Max-Planck-Institute for Molecular Plant Physiology, Am Muehlenberg 1, DE-14476 Potsdam, Germany. Phone: +49-331-567-8149, Fax: +49-331-567-898149, Email: persson{at}mpimp-golm.mpg.de
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Abstract |
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The chaperone calreticulin plays important roles in a variety of processes in the endoplasmic reticulum of animal cells, such as Ca2+ signaling and protein folding. Although the functions of calreticulin are well characterized in animals only indirect evidences are available for plants. To increase our understanding of plant calreticulins we introduced one of the Arabidopsis isoforms, AtCRT1a, into calreticulin deficient (crt-/-) mouse embryonic fibroblasts. As a result of calreticulin deficiency the mouse crt-/- fibroblasts have decreased levels of Ca2+ in the endoplasmic reticulum and impaired protein folding abilities. Expression of the AtCRT1a in mouse crt-/- fibroblasts rescued these phenotypes, that is AtCRT1a restored the Ca2+-holding capacity and chaperone functions in the endoplasmic reticulum of the mouse crt-/- fibroblasts, demonstrating that the animal sorting machinery also was functional for a plant protein, and that basic calreticulin functions are conserved across the Kingdoms. Expression analyses using a GUS- AtCRT1a promoter construct revealed high expression of CRT1a in root tips, floral tissues and in association with vascular bundles. To assess the impact of AtCRT1a in planta, we generated Atcrt1a mutant plants. The Atcrt1a mutants exhibited increased sensitivity to the drug tunicamycin, an inducer of unfolded protein response. We therefore conclude that AtCRT1a is an alleviator of the tunicamycin-induced unfolded protein response, and propose that the use of the mouse crt-/- fibroblasts as a calreticulin expression system may prove useful to assess functionalities of calreticulins from different species.
(Received January 23, 2008; Accepted April 15, 2008)
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