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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Arabidopsis Stromal 70-kD Heat Shock Proteins Are Essential for Plant Development and Important for Thermotolerance of Germinating Seeds^{1,[C],[W],[OA]}

Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan

The 70-kD heat shock proteins (Hsp70s) have been shown to be important for protein folding, protein translocation, and stress responses in almost all organisms and in almost all subcellular compartments. However, the function of plastid stromal Hsp70s in higher plants is still uncertain. Genomic surveys have revealed that there are two putative stromal Hsp70s in Arabidopsis thaliana, denoted cpHsc70-1 (At4g24280) and cpHsc70-2 (At5g49910). In this study, we show that cpHsc70-1 and cpHsc70-2 could indeed be imported into the chloroplast stroma. Their corresponding T-DNA insertion knockout mutants were isolated and designated as cphsc70-1 and cphsc70-2. No visible phenotype was observed in the cphsc70-2 mutant under normal growth conditions. In contrast, cphsc70-1 mutant plants exhibited variegated cotyledons, malformed leaves, growth retardation, and impaired root growth, even though the protein level of cpHsc70-2 was up-regulated in the cphsc70-1 mutant. After heat shock treatment of germinating seeds, root growth from cphsc70-1 seeds was further impaired, indicating that cpHsc70-1 is important for thermotolerance of germinating seeds. No cphsc70-1 cphsc70-2 double mutant could be obtained, suggesting that the cphsc70 double knockout was lethal. Genotype analyses of F₁ seedlings from various crosses indicated that double-knockout mutation was lethal to the female gametes and reduced the transmission efficiency of the male gametes. These results indicate that cpHsc70s are essential for plant development and the two cpHsc70s most likely have redundant but also distinct functions.

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: Hsou-min Li (mbhmli{at}gate.sinica.edu.tw).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.114496

^* Corresponding author; e-mail mbhmli{at}gate.sinica.edu.tw.

Received December 4, 2007; accepted January 6, 2008; published January 11, 2008.