Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA.
Plant Physiol. 2010 Apr;152(4):1951-9. doi: 10.1104/pp.110.153262. Epub 2010 Feb 24.
Galactoglycerolipids are major constituents of photosynthetic membranes in chloroplasts. At least three parallel sets of enzymes are involved in their biosynthesis that must be coordinated in response to changing growth conditions. A potential candidate for a protein affecting the activity of different galactoglycerolipid pathways is the recently described digalactosyldiacylglycerol1 (dgd1) SUPPRESSOR1 (DGS1) protein of Arabidopsis (Arabidopsis thaliana) localized in the mitochondrial outer membrane. It was discovered based on a specific gain-of-function point mutation allele, dgs1-1, that causes a partial restoration of chloroplast galactoglycerolipid deficiency in the dgd1 mutant, which is defective in the lipid galactosyltransferase, DGD1. The dgs1-1 allele causes the accumulation of hydrogen peroxide that leads to an activation of an alternative, DGD1-independent galactoglycerolipid biosynthesis pathway in chloroplasts. Analysis presented here shows that the DGS1 protein is a component of a large protein complex, which explains the previously observed dominant negative phenotype following the expression of the dgs1-1 allele. The dgs1-1 allele causes the loss of mitochondrial alternative oxidase (AOX) protein that might be related to the accumulation of hydrogen peroxide in the dgs1-1 mutant background. This effect was posttranscriptional because mRNA levels for the major form of AOX were not affected in dgs1-1 mutant seedlings. Unlike dgs1-1, a loss-of-function allele, dgs1-2, had no effect on plant growth, AOX, and lipid composition to the extent tested, leaving the quest for a possible molecular function of DGS1 open. Apparently, the DGS1 wild-type protein does not directly affect lipid metabolism in mitochondria or chloroplasts.
半乳糖甘油酯是叶绿体光合作用膜的主要成分。至少有三组平行的酶参与它们的生物合成，这些酶必须协调以响应不断变化的生长条件。一种可能影响不同半乳糖甘油酯途径活性的蛋白质候选物是最近在拟南芥（Arabidopsis thaliana）中描述的二半乳糖基二酰基甘油 1（dgd1）的抑制剂 1（DGS1）蛋白，该蛋白定位于线粒体的外膜。它是基于一个特定的功能获得点突变等位基因 dgs1-1 发现的，该等位基因导致 dgd1 突变体中叶绿体半乳糖甘油酯缺陷的部分恢复，dgd1 突变体在脂质半乳糖基转移酶 DGD1 中存在缺陷。dgs1-1 等位基因导致过氧化氢的积累，从而导致叶绿体中二半乳糖甘油酯生物合成途径的替代、DGD1 独立途径的激活。本文的分析表明，DGS1 蛋白是一个大蛋白复合物的组成部分，这解释了之前观察到的在表达 dgs1-1 等位基因后表现出的显性负表型。dgs1-1 等位基因导致线粒体替代氧化酶（AOX）蛋白的丢失，这可能与 dgs1-1 突变体背景中过氧化氢的积累有关。这种效应是转录后发生的，因为 dgs1-1 突变体幼苗中主要形式的 AOX 的 mRNA 水平没有受到影响。与 dgs1-1 不同，一种功能丧失等位基因 dgs1-2 对植物生长、AOX 和脂质组成的影响在测试范围内没有影响，这使得对 DGS1 可能的分子功能的探索仍然开放。显然，DGS1 野生型蛋白不会直接影响线粒体或叶绿体中的脂质代谢。
