1. A monogalactosyldiacylglycerol synthase found in the green sulfur bacterium Chlorobaculum tepidum reveals important roles for galactolipids in photosynthesis.
- Author
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Masuda S, Harada J, Yokono M, Yuzawa Y, Shimojima M, Murofushi K, Tanaka H, Masuda H, Murakawa M, Haraguchi T, Kondo M, Nishimura M, Yuasa H, Noguchi M, Oh-Oka H, Tanaka A, Tamiaki H, and Ohta H
- Subjects
- Amino Acid Sequence, Arabidopsis anatomy & histology, Arabidopsis enzymology, Arabidopsis genetics, Arabidopsis metabolism, Arabidopsis Proteins genetics, Arabidopsis Proteins metabolism, Bacterial Proteins classification, Bacterial Proteins genetics, Chlorobi chemistry, Chlorobi genetics, Chloroplasts metabolism, Chloroplasts ultrastructure, Galactosyltransferases classification, Galactosyltransferases genetics, Gene Knockdown Techniques, Genetic Complementation Test, Molecular Sequence Data, Phenotype, Phylogeny, Plants, Genetically Modified, Sequence Alignment, Bacterial Proteins metabolism, Chlorobi enzymology, Chlorobi physiology, Galactolipids biosynthesis, Galactosyltransferases metabolism, Photosynthesis physiology
- Abstract
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.
- Published
- 2011
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