A Cytosolic Acyltransferase Contributes to Triacylglycerol Synthesis in Sucrose-Rescued Arabidopsis Seed Oil Catabolism Mutants
A Cytosolic Acyltransferase Contributes to Triacylglycerol Synthesis in Sucrose-Rescued Arabidopsis Seed Oil Catabolism Mutants
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DOI：
10.1104/pp.112.201541
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发表时间：
2012-09-01
期刊：
影响因子：
7.4
通讯作者：
Graham, Ian A.
中科院分区：
文献类型：
--
作者：
Luisa Hernandez, M.;Whitehead, Lynne;Graham, Ian A.
三酰甘油（TAG）水平和油体在蔗糖（Suc）拯救的拟南芥（Arabidopsis thaliana）幼苗中持续存在，破坏了种子油分解代谢。本研究旨在确定当下游分解代谢被破坏时，TAG水平是否作为代谢惰性池持续存在，或者是否存在其他机制，如脂肪酸（FA）再循环进入TAG。我们发现，与干燥种子相比，这种获救的幼苗中的TAG组成发生了显著变化，其中18:2和18:3积累。然而，在幼苗中，20:1 FA不能有效地再循环成TAG，而是分解成膜脂部分和二酰基甘油。在脂解突变体糖依赖性突变体1和β -氧化双突变体acx1acx2（酰基辅酶A氧化酶）中，生长在Suc上的幼苗中TAG水平实际上增加了。我们进行了转录组学研究，发现酰基转移酶基因DIACYLGLYCEROL ACYLTRANSFERASE3 （DGAT3）上调，与花生（arachhis hypogaea）细胞质酰基转移酶同源。这种酰基转移酶的酰基辅酶A底物在油分解后脂解受阻的突变体中积累。benthamiana中的瞬时表达证实参与了TAG的合成以及对18:3和18:2 FAs的特异性。对过氧化物酶体atp结合盒转运体突变体过氧化物酶体ABC转运体1的双突变分析表明，DGAT3参与了在Suc上生长的突变苗中18:3分裂为TAG的过程。将DGAT3蛋白与绿色荧光蛋白融合，确认其定位于N. benthamiana的细胞质。这项工作已经证明，当种子油分解在一个涉及可溶性细胞质酰基转移酶的过程中被阻断时，18:2和18:3脂肪酸被积极地再循环成TAG。
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 dependent1and the beta-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.