Arabidopsis stromal 70-kDa heat shock proteins are essential for chloroplast development
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70 kDa heat shock proteins (Hsp70s) act as molecular chaperones involved in essential cellular processes such as protein folding and protein transport across membranes. They also play a role in the cell’s response to a wide range of stress conditions. The Arabidopsis family of Hsp70s homologues includes two highly conserved proteins, cpHsc70-1 and cpHsc70-2 which are both imported into chloroplasts (Su and Li in Plant Physiol 146:1231–1241, 2008). Here, we demonstrate that YFP-fusion proteins of both cpHsc70-1 and cpHsc70-2 are predominantly stromal, though low levels were detected in the thylakoid membrane. Both genes are ubiquitously expressed at high levels in both seedlings and adult plants. We further show that both cpHsc70-1 and cpHsc70-2 harbour ATPase activity which is essential for Hsp70 chaperone activity. A previously described T-DNA insertion line for cpHsc70-1 (ΔcpHsc70-1) has variegated cotyledons, malformed leaves, growth retardation, impaired root growth and sensitivity to heat shock treatment. In addition, under stress conditions, this mutant also exhibits unusual sepals, and malformed flowers and sucrose concentrations as low as 1% significantly impair growth. cpHsc70-1/cpHsc70-2 double-mutants are lethal. However, we demonstrate through co-suppression and artificial microRNA (amiRNA) approaches that transgenic plants with severely reduced levels of both genes have a white and stunted phenotype. Interestingly, chloroplasts in these plants have an unusual morphology and contain few or no thylakoid membranes. Our data show that cpHsc70-1 and cpHsc70-2 are essential ATPases, have overlapping roles and are required for normal plastid structure.
KeywordsArtificial microRNA ATPase Chloroplast Hsp70 Photosynthesis Stroma Thylakoid
Yellow fluorescent protein
70 kDa heat shock proteins
Vesicle inducing protein in plastids 1
We thank Natalie Allcock and Stefan Hyman for the electron microscopy, NASC for providing the seeds for the T-DNA insertion lines, Plant systems Biology at VIB-Ghent University for providing the vector pB7YWG2 and Mark Curtis at the University of Zurich for the pMDC vectors. We also thank Poul Eric Jensen (University of Copenhagen, Denmark) for providing PsaF and PsaD antibodies. This work was financed by a grant from The Norwegian Research Council (178071) to Simon Geir Møller.
- Peltier JB, Cai Y, Sun Q, Zabrouskov V, Giacomelli L, Rudella A, Ytterberg AJ, Rutschow H, van Wijk KJ (2006) The oligomeric stromal proteome of Arabidopsis thaliana chloroplasts. Mol Cell Proteomics 5:114–133Google Scholar
- Seigneurin-Berny D, Salvi D, Joyard J, Rolland N (2008) Purification of intact chloroplasts from Arabidopsis and spinach leaves by isopycnic centrifugation. Curr Protoc Cell Biol Chapter 3:Unit 3.30Google Scholar
- Zybailov B, Rutschow H, Friso G, Rudella A, Emanuelsson O, Sun Q, van Wijk KJ (2008) Sorting signals, N-terminal modifications and abundance of the chloroplast proteome. PLoS One 3:e1994Google Scholar
- Zybailov B, Friso G, Kim J, Rudella A, Rodríguez VR, Asakura Y, Sun Q, van Wijk KJ (2009b) Large scale comparative proteomics of a chloroplast Clp protease mutant reveals folding stress, altered protein homeostasis, and feedback regulation of metabolism. Mol Cell Proteomics 8:1789–1810CrossRefPubMedGoogle Scholar