A Monogalactosyldiacylglycerol Synthase Found in the Green Sulfur Bacterium Chlorobaculum tepidum Reveals Important Roles for Galactolipids in Photosynthesis
A Monogalactosyldiacylglycerol Synthase Found in the Green Sulfur Bacterium Chlorobaculum tepidum Reveals Important Roles for Galactolipids in Photosynthesis
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DOI：
10.1105/tpc.111.085357
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发表时间：
2011-07-01
期刊：
影响因子：
11.6
通讯作者：
Ohta, Hiroyuki
中科院分区：
文献类型：
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作者：
Masuda, Shinji;Harada, Jiro;Ohta, Hiroyuki
单半乳糖基甘油二酯（MGDG）是地球上最丰富的天然极性脂质，几乎在所有光合生物中都是保守的。在植物中，MGDG高度积累在叶绿体膜上，是类囊体膜的重要组成部分。然而，MGDG在光合作用中的确切功能尚未得到很好的理解。在这里，我们报告了一种新的MGDG合酶从绿色硫细菌Chlorobaculum tepidum。该酶MgdA使用UDP-Gal作为底物催化MGDG合成。编码MgdA的基因是这种细菌所必需的，只有杂合的mgdA突变体可以分离。一个mgdA敲低突变影响在体内组装的细菌叶绿素c聚集体，这表明参与的MGDG在建设的光捕获复合物称为叶绿体。这些结果表明，MGDG生物合成已独立建立在每个光合生物进行光合作用在不同的环境条件下。我们通过异源表达MgdA来补充拟南芥MGDG合酶突变体。补充植物表现出几乎正常水平的MGDG，虽然他们也有异常的形态表型，包括叶绿素含量降低，没有顶端优势的芽生长，非典型花发育，不育。这些观察结果提供了新的见解有关的重要性，调节MGDG合成在高等植物的生理。
Monogalactosyldiacylglycerol (MGDG), which is conserved in almost all photosynthetic organisms, is the most abundant natural polar lipid on Earth. In plants, MGDG is highly accumulated in the chloroplast membranes and is an important bulk constituent of thylakoid membranes. However, precise functions of MGDG in photosynthesis have not been well understood. Here, we report a novel MGDG synthase from the green sulfur bacterium Chlorobaculum tepidum. This enzyme, MgdA, catalyzes MGDG synthesis using UDP-Gal as a substrate. The gene encoding MgdA was essential for this bacterium; only heterozygous mgdA mutants could be isolated. An mgdA knockdown mutation affected in vivo assembly of bacteriochlorophyll c aggregates, suggesting the involvement of MGDG in the construction of the light-harvesting complex called chlorosome. These results indicate that MGDG biosynthesis has been independently established in each photosynthetic organism to perform photosynthesis under different environmental conditions. We complemented an Arabidopsis thaliana MGDG synthase mutant by heterologous expression of MgdA. The complemented plants showed almost normal levels of MGDG, although they also had abnormal morphological phenotypes, including reduced chlorophyll content, no apical dominance in shoot growth, atypical flower development, and infertility. These observations provide new insights regarding the importance of regulated MGDG synthesis in the physiology of higher plants.