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Oxygenic photosynthesis without galactolipids

Glycolipid biosynthetic pathway elucidated 30 years after suggestion

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Graduate School of Arts and Sciences / College of Arts and Sciences
2014/09/30

Professor Naoki Sato at the University of Tokyo, in collaboration with Associate Professor Koichiro Awai at Shizuoka University and Professor Hiroyuki Ohta at the Tokyo Institute of Technology, has identified the complete pathway of glycolipid biosynthesis in cyanobacteria, and at the same time, demonstrated that galactolipids, which are always present in photosynthetic organisms, are not necessary for photosynthesis.

Comparison of galactolipid biosynthetic pathways in cyanobacteria, red algae, and green plants. The mgdE gene encodes the epimerase that catalyzes the conversion of glucolipids (GlcDG) to galactolipids (MGDG). Only cyanobacteria have this gene. In contrast, in red algae and green plants, MGDG is directly synthesized by transfer of galactose to diacylglycerol.

© 2014 Naoki Sato.
Comparison of galactolipid biosynthetic pathways in cyanobacteria, red algae, and green plants.
The mgdE gene encodes the epimerase that catalyzes the conversion of glucolipids (GlcDG) to galactolipids (MGDG). Only cyanobacteria have this gene. In contrast, in red algae and green plants, MGDG is directly synthesized by transfer of galactose to diacylglycerol.

Cyanobacteria are prokaryotes (single-celled organisms that lack membrane-bound organelles such as a nucleus) that perform oxygenic photosynthesis (a type of photosynthesis that produces oxygen), and are believed to be the origin of the chloroplasts found inside the cells of plants and algae. The initial reactions in the process of photosynthesis occur in the photosynthetic membranes that consist of galactolipids (containing one or two galactose moieties), which is therefore believed to be necessary for photosynthesis. Further, cyanobacteria synthesize glycolipids in the process of converting glucolipids to galactolipids.

In this research the group identified the gene mgdE that encodes the enzyme that converts glucolipid to galactolipid. By disrupting this gene, the group demonstrated that oxygenic photosynthesis is possible with a photosynthetic membrane consisting only of glucolipids, overturning the current understanding of the photosynthetic process. Professor Sato proposed the route for glycolipid synthesis in his doctoral thesis 30 years ago. With this discovery, the genes for all the enzymes in the route for glycolipid synthesis, first proposed by Professor Sato in his doctoral thesis 30 years ago, have been identified.

Paper

K. Awai, H. Ohta and N. Sato,
“Oxygenic photosynthesis without galactolipids”,
Proceedings of the National Academy of Sciences Online Edition: 2014/9/2 (Japan time), doi: 10.1073/pnas.1403708111.
Article link

Links

Graduate School of Arts and Sciences

Department of Life Sciences, Graduate School of Arts and Sciences (Japanese)

Sato Laboratory, Department of Life Sciences, Graduate School of Arts and Sciences

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