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BIOENERGETICS AND PHOTOSYNTHESIS

Reduction of Plastid-Localized Carbonic Anhydrase Activity Results in Reduced Arabidopsis Seedling Survivorship^1,[W],[OA]

Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2

Carbonic anhydrase (CA; EC 4.2.1.1) catalyzes the interconversion of CO₂ and HCO₃^– and is a major protein constituent of the C₃ higher plant chloroplast where it is presumed to play a role in photosynthetic carbon assimilation. In this study, we have used both RNA antisense and gene knockout lines to specifically reduce the activity of the chloroplast βCA1 polypeptide (At3g01500) in the model plant Arabidopsis (Arabidopsis thaliana). Although able to germinate, seedling establishment of transgenic plants is significantly reduced relative to wild-type plants when grown at ambient levels of CO₂. Growth at elevated (1,500 µL L^–1) CO₂ or on plates supplemented with sucrose restores seedling establishment rates to wild-type levels. Seed from wild-type and transgenic plants exhibited no significant differences in seed protein, lipid content, or reserve mobilization during seedling growth. βCA1-deficient seedlings do, however, exhibit reduced capacity for light-dependent ¹⁴CO₂ assimilation prior to the development of true leaves. The small number of surviving seedlings able to grow and develop are phenotypically similar to wild-type plants, even when subsequently grown at subambient levels of CO₂. Microarray analysis of mature leaves of βCA1-deficient plants shows some differences in transcript abundance, particularly with genes involved in ethylene signaling and response. The data suggest that reduced levels of seedling establishment by βCA1-deficient plants could be the result of poor cotyledon photosynthetic performance at the onset of phototrophic growth and prior to the development of true leaves.

² These authors contributed equally to the article.

³ Present address: Department of Biology, University of North Carolina, Chapel Hill, NC 27599.

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: John R. Coleman (coleman{at}csb.utoronto.ca).

^[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.108.118661

^* Corresponding author; e-mail coleman{at}csb.utoronto.ca.

Received March 5, 2008; accepted April 4, 2008; published April 23, 2008.

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