Abstract:

We tested the hypothesis that peroxisomal citrate synthase (CSY) is required for carbon transfer from peroxisomes to mitochondria during respiration of triacylglycerol in Arabidopsis thaliana seedlings. Two genes encoding peroxisomal CSY are expressed in Arabidopsis seedlings, and seeds from plants with both CSY genes disrupted were dormant and did not metabolize triacylglycerol. Germination was achieved by removing the seed coat and supplying sucrose, but the seedlings still did not use triacylglycerol. The mutant seedlings were resistant to 2,4-dichlorophenoxybutyric acid, indicating a block in peroxisomal beta-oxidation, and were unable to develop further after transfer to soil. The mutant phenotype was complemented with a cDNA encoding CSY with either its native peroxisomal targeting sequence (PTS2) or a heterologous PTS1 sequence from pumpkin (Cucurbita pepo) malate synthase. These results suggest that peroxisomal CSY in Arabidopsis is not only a key enzyme of the glyoxylate cycle but also catalyzes an essential step in the respiration of fatty acids. We conclude that citrate is exported from the peroxisome during fatty acid respiration, whereas in yeast, acetylcarnitine is exported.

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Arabidopsis Peroxisomal Citrate Synthase Is Required for Fatty Acid Respiration and Seed Germination<sup><a href="#fn3" rid="fn3" class=" fn">W⃞</a></sup>

Itsara Pracharoenwattana

Johanna Cornah

Steven Smith

Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JH, United Kingdom

^{Current address: Department of Biology, University of York, PO Box 373, York YO10 5YW, UK.}

^{Current address: School of Biomedical and Chemical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.}

^{To whom correspondence should be addressed. E-mail}ua.ude.awu.enellyc@htimss; fax 61-8-6488-4404.

Received 2005 Feb 16; Revised 2005 Apr 7; Accepted 2005 Apr 7.

Abstract

We tested the hypothesis that peroxisomal citrate synthase (CSY) is required for carbon transfer from peroxisomes to mitochondria during respiration of triacylglycerol in Arabidopsis thaliana seedlings. Two genes encoding peroxisomal CSY are expressed in Arabidopsis seedlings, and seeds from plants with both CSY genes disrupted were dormant and did not metabolize triacylglycerol. Germination was achieved by removing the seed coat and supplying sucrose, but the seedlings still did not use triacylglycerol. The mutant seedlings were resistant to 2,4-dichlorophenoxybutyric acid, indicating a block in peroxisomal β-oxidation, and were unable to develop further after transfer to soil. The mutant phenotype was complemented with a cDNA encoding CSY with either its native peroxisomal targeting sequence (PTS2) or a heterologous PTS1 sequence from pumpkin (Cucurbita pepo) malate synthase. These results suggest that peroxisomal CSY in Arabidopsis is not only a key enzyme of the glyoxylate cycle but also catalyzes an essential step in the respiration of fatty acids. We conclude that citrate is exported from the peroxisome during fatty acid respiration, whereas in yeast, acetylcarnitine is exported.

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Acknowledgments

We thank Carlo van Roermund (University of Amsterdam, Amsterdam, The Netherlands), Dick Trelease (Arizona State University, Tempe, AZ), and Ian Graham (University of York, York, UK) for critically reading the manuscript. We also thank Imogen Sparkes (Oxford Brookes University, Oxford, UK) for verifying peroxisomal targeting of mRFP, Robert Smith (University of Edinburgh, Edinburgh, UK) for gas chromatography–mass spectrometry analysis, Graham Wright (University of Edinburgh) for confocal microscopy, John Findlay (University of Edinburgh) for electron microscopy, and Yi Li (University of York, York, UK) for advice on phylogenetic analysis. We gratefully acknowledge financial support from the Thai Government Development and Promotion of Science and Technology Talents Project PhD studentship awarded to I.P., the Leverhulme Trust (research fellowship awarded to S.M.S.), and the Biotechnology and Biological Sciences Research Council (Research Grant P13859 awarded to S.M.S.).

Acknowledgments

Notes

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.plantcell.org) is: Steven M. Smith (ua.ude.awu.enellyc@htimss).

^{Online version contains Web-only data.}

Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.105.031856.

Notes

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.plantcell.org) is: Steven M. Smith (ua.ude.awu.enellyc@htimss).Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.105.031856.

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