Digalactosyldiacylglycerol (DGDG), One of the Unique Plant-specific Glycolipids is a Key for Forming a Tiny “Jungle Gym” in an Organelle Etioplast During Growth in the Dark

LastUpDate： August 06, 2018

Main point of research

Our research group performed a study on digalactosyldiacylglycerol (DGDG) revealing an essential role of this glycolipid in forming prolamellar bodies during seedling and etioplast-development period in the dark.
A glycolipid DGDG was found to play an important role for etioplasts developing prolamellar body, which is a regular lattice membrane structure that looks like a tiny jungle gym.
Clarifying the detailed role of DGDG in the development and function of etioplast will contribute to elucidate complex systems of plant growth with photosynthesis.

Authors

Sho Fujii, graduate student, Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo
Hajime Wada, Professor, Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo
Koichi Kobayashi, Associate Professor, Faculty of Liberal Arts and Sciences, Osaka Prefecture University

Overview of research

Etioplast-development

When angiosperm seeds germinate in the dark, they develop etiolated seedlings with non-green cotyledons. The dark-grown seedlings do not contain chloroplasts or green photosynthetic organelles in cotyledon cells. Instead, yellowish chloroplast precursors called etioplasts(*1) are developed. When cotyledon cells are exposed to light, etioplasts quickly transform into green chloroplasts and start photosynthesis.
Inside etioplasts, named prolamellar body, a regular lattice membrane structure that looks like a tiny jungle gym, is structured. Plant-specific glycolipids(*2) are the major constituent elements of prolamellar bodies, but their roles in the formation and function of prolamellar bodies remained unknown.

Sho Fujii, Graduate student, Graduate School of Arts and Sciences, The University of Tokyo, Dr. Koichi Kobayashi, Faculty of Liberal Arts and Sciences, Osaka Prefecture University, corresponding author, Prof. Tatsuru Masuda, Prof. Hajime Wada, Graduate School of Arts and Sciences, The University of Tokyo and Prof. Noriko Nagata, Faculty of Science, Japan Women’s University performed a study on digalactosyldiacylglycerol (DGDG), a unique glycolipids abundant in prolamellar bodies, to elucidate how plants form prolamellar bodies and exert their functions in the dark.
The research group examined an Arabidopsis(*3) mutant of which ability to produce DGDG was largely decreased, and found that loss of DGDG strongly disturbed the jungle gym structure of prolamellar bodies. This finding confirmed an essential role of this glycolipid in forming such unique structure. They also revealed that DGDG was required for the biosynthesis of pigments being accumulated as precursor to chlorophyll(*4) in prolamellar bodies.

While these lipids and pigments are essential for developing the thylakoid membrane(*5), the site of light-dependent photosynthetic reactions, the jungle gym structure of prolamellar bodies formed by glycolipids would help dark-grown plants to establish photosynthetic growth soon after exposure to light. These findings shed light on the unique role of DGDG in dark-to-light adaptation of plants and contribute to elucidate complex systems of plant growth with photosynthesis.

The research findings were published in an online journal of Plant Physiology.

Article Title: Digalactosyldiacylglycerol is essential for organization of the membrane structure in etioplasts

Glossaries

*1 Etioplast

Etioplasts are organelles containing prolamellar bodies which are membrane aggregations arranged in pattern of a tiny jungle gym. They are found in angiosperms grown in the dark. They are transformed into chloroplasts soon after exposure to light.

*2 Glycolipid

Glycolipids are lipids with sugars in their polar head groups. In plants and algae, there are three major glyceroglycolipids accounting for 90% of the chloroplast membrane lipid.

*3 Arabidopsis thaliana

Arabidopsis thaliana is an annual plant of Brassicaceae family. It was the first plant to have its genome sequenced, and its mutant collections, transgenic lines, research findings and data are available globally at various research institutes.

*4 Chlorophyll

Chlorophyll is green pigments found in the chloroplasts of algae and plants. It is an essential element for photosynthesis. The major function of chlorophyll is to absorb light energy for photosynthetic reactions.

*5 Thylakoid membrane

Thylakoid membrane is membrane structure with disk-shaped sacks inside chloroplasts. It is the site of the primary photosynthetic reactions. The lipid bilayer of the membrane mainly consists of glycolipids which allow chlorophyll and protein to accumulate.