Journal Article

A Cytosolic Acyltransferase Contributes to Triacylglycerol Synthesis in Sucrose-Rescued Arabidopsis Seed Oil Catabolism Mutants

Kozhevnikova, Ekaterina, Larson, Tony R., He, Zhesi, Gilday, Alison, Whitehead, Lynne, Gazda, Valeria, Graham, Ian A., Hernández, M. Luisa, Vaistij, Fabián E.

2012

Overview

Triacylglycerol (TAG) levels and oil bodies persist in sucrose (Suc)-rescued Arabidopsis (Arabidopsis thaliana) seedlings disrupted in seed oil catabolism. This study set out to establish if TAG levels persist as a metabolically inert pool when downstream catabolism is disrupted, or if other mechanisms, such as fatty acid (FA) recycling into TAG are operating. We show that TAG composition changes significantly in Suc-rescued seedlings compared with that found in dry seeds, with 18:2 and 18:3 accumulating. However, 20:1 FA is not efficiently recycled back into TAG in young seedlings, instead partitioning into the membrane lipid fraction and diacylglycerol. In the lipolysis mutant sugar dependent1 and the β-oxidation double mutant acx1acx2 (for acyl-Coenzyme A oxidase), levels of TAG actually increased in seedlings growing on Suc. We performed a transcriptomic study and identified up-regulation of an acyltransferase gene, DIACYLGLYCEROL ACYLTRANSFERASE3 (DGAT3), with homology to a peanut (Arachis hypogaea) cytosolic acyltransferase. The acyl-Coenzyme A substrate for this acyltransferase accumulates in mutants that are blocked in oil breakdown postlipolysis. Transient expression in Nicotiana benthamiana confirmed involvement in TAG synthesis and specificity toward 18:3 and 18:2 FAs. Double-mutant analysis with the peroxisomal ATP-binding cassette transporter mutant peroxisomal ABC transporter1 indicated involvement of DGAT3 in the partitioning of 18:3 into TAG in mutant seedlings growing on Suc. Fusion of the DGAT3 protein with green fluorescent protein confirmed localization to the cytosol of N. benthamiana. This work has demonstrated active recycling of 18:2 and 18:3 FAs into TAG when seed oil breakdown is blocked in a process involving a soluble cytosolic acyltransferase.

• Publisher: American Society of Plant Biologists
• Subject: ABC transporters / Agrobacterium tumefaciens - genetics / Agrobacterium tumefaciens - metabolism / Amino Acid Sequence / Arabidopsis - enzymology / Arabidopsis - genetics / Arabidopsis Proteins - genetics / Arabidopsis Proteins - metabolism / Arabidopsis thaliana / Arachis - enzymology / Arachis - genetics / Arachis hypogaea / beta oxidation / BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES / Biological and medical sciences / cytosol / Cytosol - enzymology / Diacylglycerol O-Acyltransferase - genetics / Diacylglycerol O-Acyltransferase - metabolism / diacylglycerols / Diglycerides / Fatty acids / Fatty Acids - metabolism / Fundamental and applied biological sciences. Psychology / Gene Expression Profiling - methods / gene expression regulation / Gene Expression Regulation, Plant / Genes / Genes, Plant / Germination / green fluorescent protein / Lipid bodies / Lipid Metabolism / Lipids / lipolysis / mutants / Nicotiana - genetics / Nicotiana - metabolism / Nicotiana benthamiana / peanuts / Peroxisomes / Peroxisomes - enzymology / Plant Oils - metabolism / Plant physiology and development / Plants / seed oils / Seedlings / Seedlings - metabolism / Seeds / Seeds - genetics / Seeds - metabolism / Sequence Homology, Amino Acid / sucrose / Sucrose - metabolism / transcriptomics / triacylglycerols / Triglycerides / Triglycerides - biosynthesis