Abstract:

Triacylglycerol hydrolysis (lipolysis) plays a pivotal role in the life cycle of many plants by providing the carbon skeletons and energy that drive postgerminative growth. Despite the physiological importance of this process, the molecular mechanism is unknown. Here, a genetic screen has been used to identify Arabidopsis thaliana mutants that exhibit a postgerminative growth arrest phenotype, which can be rescued by providing sugar. Seventeen sugar-dependent (sdp) mutants were isolated, and six represent new loci. Triacylglycerol hydrolase assays showed that sdp1, sdp2, and sdp3 seedlings are deficient specifically in the lipase activity that is associated with purified oil bodies. Map-based cloning of SDP1 revealed that it encodes a protein with a patatin-like acyl-hydrolase domain. SDP1 shares this domain with yeast triacylglycerol lipase 3 and human adipose triglyceride lipase. In vitro assays confirmed that recombinant SDP1 hydrolyzes triacylglycerols and diacylglycerols but not monoacylglycerols, phospholipids, galactolipids, or cholesterol esters. SDP1 is expressed predominantly in developing seeds, and a SDP1-green fluorescent protein fusion was shown to associate with the oil body surface in vivo. These data shed light on the mechanism of lipolysis in plants and establish that a central component is evolutionarily conserved among eukaryotes.

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SUGAR-DEPENDENT1 Encodes a Patatin Domain Triacylglycerol Lipase That Initiates Storage Oil Breakdown in Germinating Arabidopsis Seeds<a href="#fn1" rid="fn1" class=" fn">[W]</a>

Peter Eastmond

Department of Biology, Centre for Novel Agricultural Products, University of York, York YO10 5YW, United Kingdom

^{To whom correspondence should be addressed. E-mail}ku.ca.kroy@4ejp; fax 44-01904-328762.

Received 2005 Dec 21; Revised 2005 Dec 21; Accepted 2006 Jan 18.

Abstract

Triacylglycerol hydrolysis (lipolysis) plays a pivotal role in the life cycle of many plants by providing the carbon skeletons and energy that drive postgerminative growth. Despite the physiological importance of this process, the molecular mechanism is unknown. Here, a genetic screen has been used to identify Arabidopsis thaliana mutants that exhibit a postgerminative growth arrest phenotype, which can be rescued by providing sugar. Seventeen sugar-dependent (sdp) mutants were isolated, and six represent new loci. Triacylglycerol hydrolase assays showed that sdp1, sdp2, and sdp3 seedlings are deficient specifically in the lipase activity that is associated with purified oil bodies. Map-based cloning of SDP1 revealed that it encodes a protein with a patatin-like acyl-hydrolase domain. SDP1 shares this domain with yeast triacylglycerol lipase 3 and human adipose triglyceride lipase. In vitro assays confirmed that recombinant SDP1 hydrolyzes triacylglycerols and diacylglycerols but not monoacylglycerols, phospholipids, galactolipids, or cholesterol esters. SDP1 is expressed predominantly in developing seeds, and a SDP1–green fluorescent protein fusion was shown to associate with the oil body surface in vivo. These data shed light on the mechanism of lipolysis in plants and establish that a central component is evolutionarily conserved among eukaryotes.

Abstract

The values are the mean ± se of measurements from four separate incubations. The final concentration used was equivalent to 10 mM for all substrates, with the exception of oleoyl-CoA and p-nitrophenyl palmitate, which were 100 μM. Inhibitors were incubated with rSDP1 for 15 min before the substrate was added. ND, not detected; E₆₀₀, diethyl-p-nitrophenyl phosphate; DFP, diisopropyl fluorophosphate; BEL, [E]-6-[bromoethylene]-3-[1-naphthalenyl]-2H-tetrahydropyran-2-one.

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Acknowledgments

I thank Lynda Sainty for her invaluable technical assistance. I also thank Karen Chance and Meg Stark from the University of York Biology Department Technology Facility for their assistance with sample preparation and analysis using confocal and electron microscopy. This work was funded by the Biotechnology and Biological Sciences Research Council via a David Phillips Research Fellowship (87/JF/16985) awarded to P.J.E.

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: Peter J. Eastmond (ku.ca.kroy@4ejp).

^{Online version contains Web-only data.}

Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.105.040543.

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: Peter J. Eastmond (ku.ca.kroy@4ejp).Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.105.040543.

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<em>SUGAR-DEPENDENT1</em> Encodes a Patatin Domain Triacylglycerol Lipase That Initiates Storage Oil Breakdown in Germinating <em>Arabidopsis</em> Seeds<sup><a href="#fn1" rid="fn1" class=" fn">[W]</a></sup>

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