Journal Article

Lipid Transport Mediated by Arabidopsis TGD Proteins is Unidirectional from the Endoplasmic Reticulum to the Plastid

Changcheng Xu, Eric R. Moellering, Bagyalakshmi Muthan, Jilian Fan and Christoph Benning

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 6, pages 1019-1028
Published in print June 2010 | ISSN: 0032-0781
Published online April 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq053
Lipid Transport Mediated by Arabidopsis TGD Proteins is Unidirectional from the Endoplasmic Reticulum to the Plastid

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The transfer of lipids between the endoplasmic reticulum (ER) and the plastid in Arabidopsis involves the TRIGALACTOSYLDIACYLGLYCEROL (TGD) proteins. Lipid exchange is thought to be bidirectional based on the presence of specific lipid molecular species in Arabidopsis mutants impaired in the desaturation of fatty acids of membrane lipids in the ER and plastid. However, it was unclear whether TGD proteins were required for lipid trafficking in both directions. This question was addressed through the analysis of double mutants of tgd1-1 or tgd4-3 in genetic mutant backgrounds leading to a defect in lipid fatty acid desaturation either in the ER (fad2) or the plastid (fad6). The fad6 tgd1-1 and fad6 tgd4-3 double mutants showed drastic reductions in the relative levels of polyunsaturated fatty acids and of galactolipids. The growth of these plants and the development of photosynthetic membrane systems were severely compromised, suggesting a disruption in the import of polyunsaturated fatty acid-containing lipid species from the ER. Furthermore, a forward-genetic screen in the tgd1-2 dgd1 mutant background led to the isolation of a new fad6-2 allele with a marked reduction in the amount of digalactosyldiacylglycerol. In contrast, the introduction of fad2, affecting fatty acid desaturation of lipids in the ER, into the two tgd mutant backgrounds did not further decrease the level of fatty acid desaturation in lipids of extraplastidic membranes. These results suggest that the role of TGD proteins is limited to plastid lipid import, but does not extend to lipid export from the plastid to extraplastidic membranes.

Keywords: Fatty acid desaturase; Galactolipid; Lipid transport; TGD protein

Journal Article.  5309 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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