A Monogalactosyldiacylglycerol Synthase Found in the Green Sulfur Bacterium Chlorobaculum tepidum Reveals Important Roles for Galactolipids in Photosynthesis

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 function...

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Published in:	The Plant cell Vol. 23; no. 7; pp. 2644 - 2658
Main Authors:	Masuda, Shinji, Harada, Jiro, Yokono, Makio, Yuzawa, Yuichi, Shimojima, Mie, Murofushi, Kazuhiro, Tanaka, Hironori, Masuda, Hanako, Murakawa, Masato, Haraguchi, Tsuyoshi, Kondo, Maki, Nishimura, Mikio, Yuasa, Hideya, Noguchi, Masato, Oh-oka, Hirozo, Tanaka, Ayumi, Tamiaki, Hitoshi, Ohta, Hiroyuki
Format:	Journal Article
Language:	English
Published:	United States American Society of Plant Biologists 01-07-2011
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 Bacterial Proteins - metabolism Biosynthesis Chlorobi Chlorobi - chemistry Chlorobi - enzymology Chlorobi - genetics Chlorobi - physiology Chloroplasts Chloroplasts - metabolism Chloroplasts - ultrastructure Environmental conditions Enzymes Galactolipids Galactolipids - biosynthesis Galactosyltransferases - classification Galactosyltransferases - genetics Galactosyltransferases - metabolism Gene Knockdown Techniques Genetic Complementation Test Infertility Lipids Molecular Sequence Data Phenotype Photosynthesis Photosynthesis - physiology Phylogeny Plant cells Plants Plants, Genetically Modified Polymerase chain reaction Sequence Alignment Sulfur
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Summary:	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 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.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 The author responsible for distribution of materials integral to the findings presented in this article in according with the policy described in the Instructions for Authors (www.plantcell.org) is: Shinji Masuda (shmasuda@bio.titech.ac.jp). www.plantcell.org/cgi/doi/10.1105/tpc.111.085357 Online version contains Web-only data.
ISSN:	1040-4651 1532-298X
DOI:	10.1105/tpc.111.085357