Plants

Discovery of new metabolic pathways to synthesize seed oils | RIKEN

April 4, 2022

Riken

-Possible metabolic modification technology for biofuel production-

An international collaborative research team led by Tomoki Nakamura, head of the Plant Lipid Research Group at the Center for Sustainable Resource Science at the RIKEN, discovered the triacylglycerol (TAG), the main component of seed oil.[1]A new anabolic pathway was discovered.

The result of this study is biodiesel.[2]Metabolic engineering for large-scale production of raw materials, such as[3]expected to contribute.

TAG is synthesized from phosphatidylcholine (PC), the predominant phosphatide constituting cell membranes, but it is unclear how the second predominant phosphatidylethanolamine (PE) is converted to TAG.

This time, the international collaborative research team focused on the presence of enzymes that directly convert PE into PC in yeast and human liver, and on the model plant Arabidopsis thaliana.[4]PLMT, an enzyme that works the same way[5]I found it. Overproduction of PLMT in plants increases the TAG content of seeds to up to 20% per dry weight. On the other hand, overproduction of PLMT was also found to inhibit the growth of leaves, etc., suggesting that this metabolic pathway may be specialized for the synthesis of seed TAG. These results suggest that PLMT is involved in the synthesis of seed TAGs by converting PE to PC.

This study is based on scientific journals”Journal of Experimental BotanyIt was released in an online version (April 1).

background

Triacylglycerols (TAGs), the main constituent of seed oils, are important not only for plant growth and development, but also for biofuels such as biodiesel.[2]It is used as a raw material in various industries.

As the seed grows, TAG is synthesized from the phospholipids that make up the cell membrane. So far, the metabolic mechanism for the conversion of the most predominant phosphatidylcholine (PC) to TAG has been well studied, but how the second predominant phosphatidylethanolamine (PE) is converted is unclear. Label.

Research Methods and Results

The international collaborative research team first focused on the fact that yeast and human liver have enzymes that convert PE into PC, and used the model plant Arabidopsis thaliana to demonstrate that a similar reaction occurs in plants.

Next, when plants overproduced PLMT, the enzyme that catalyzes this reaction, the TAG content of the seeds increased up to about 20%/dry weight. On the other hand, overproduction of PLMT was found to inhibit leaf growth, etc., suggesting that this metabolic pathway may be a specialized mechanism for seed TAG synthesis.

From these results, it is clear that seeds can efficiently synthesize TAG by converting PE to PC using PLMT (see figure below).

Previously known TAG synthesis roadmap (left) and newly discovered roadmap

Diagram of previously known TAG synthesis routes (left) and newly discovered routes

The primary phospholipid, phosphatidylcholine (PC), is converted to TAG in one or two-step reactions via the intermediate diacylglycerol (DAG). On the other hand, it is unclear how the second major phosphatide, phosphatidylethanolamine (PE), is converted to TAG (left). It was revealed that PE was once converted to PC and then supplied to TAG synthesis via a new pathway catalyzed by the enzyme PLMT (right).

future expectations

This time, the metabolic pathway that converts PE to TAG has been elucidated. This will create a new method for metabolic engineering to convert phospholipids into TAGs more efficiently and is expected to be used in the development of production technologies such as biofuels.

The research results are the 17 “Sustainable Development Goals (SDGs)” formulated by the United Nations in 2016.[6]Among them, contribute to “2. Zero Hunger”, “3. Health and well-being for all”, “13. Concrete measures to combat climate change” and “15. Protect rich land”.

Supplementary Instructions

  • 1.Triacylglycerol (TAG)
    Also known as triglycerides. It is a lipid compound bound by three long-chain fatty acid ester bonds on the glycerol backbone. It is the main component of seed oil and is also abundant in oil droplets of animal cells. Although it has no polarity and is therefore not a component of biofilms, it has also received attention as a feedstock for biofuels due to its role as an energy storage substance.
  • 2.biodiesel, biofuel
    Fuels made from biological resources derived from animals and plants are called biofuels, and those suitable for use as diesel engine fuels are called biodiesel. TAG is rich in fatty acid methyl esters and is a feedstock for biodiesel.
  • 3.metabolic engineering
    A technique for producing useful compounds by arbitrarily altering the metabolic flux of an organism through genetic recombination techniques. It can be said that it is one of the ultimate “manufacturing” to give full play to biological capabilities.
  • 4.Arabidopsis
    Cruciferous annual plant. Because of its small genome size, short generation, easy cultivation, and easy gene transfer, it is used as a model organism for seed plant research.
  • 5.Enzyme PLMT
    The official name is phospholipid n– Methyltransferase. Generic term for enzymes with the activity of adding methyl groups to phosphatidyl ethanolamine (PE) and its methylated derivatives. When PE is methylated 3 times, phosphatidylcholine (PC) is produced.
  • 6.Sustainable Development Goals (SDGs)
    International goals for the period 2016 to 2030 are set out in the 2030 Agenda for Sustainable Development, adopted at the United Nations summit in September 2015. Composed of 17 goals and 169 goals, the realization of a sustainable world is a common thing, not only developing countries, but also developed countries themselves are working hard, and Japan is also actively working on it. (Reprinted from the website of the Ministry of Foreign Affairs with some modifications).

International Collaborative Research Team

RIKEN Sustainable Resource Science Center Plant Lipid Research Team
Captain Nakamura Yuki
(Researcher/Professor, Institute of Plant and Microbiology, National Chung Hsing University, Professor, Biotechnology Center, National Chung Hsing University)

Department of Bioengineering, Graduate School, National Chung Hsing University (Taiwan)
Doctor of Science, Taiwan International Graduate Program
(Institute of Plant and Microbiology, Academia Sinica (Taiwan))

research support

This research was supported by the “Rising Star Award (Winner: Tomoki Nakamura)” of the Academy of Science and Technology (Taiwan).

Base paper information

  • Yue-Rong Tan and Yuki Nakamura, “The Importance of Phospholipids in Arabidopsis n-The role of methyltransferase (PLMT) in glycerolipid metabolism and plant growth”, Journal of Experimental Botany10.1093/jxb/erac049

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Plant Lipids Research Group, RIKEN Center for Sustainable Resource Science
Captain Nakamura Yuki

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