Scientists Shed Light On A Piece Of Photosynthesis

MSU scientists have isolated a gene responsible for making an abundant yet enigmatic piece of a plant's makeup. The discovery, reported in this week's edition of Science magazine, opens the gates to a more complete understanding of energy conversion in plants.

The gene that Christoph Benning, assistant professor of biochemistry, and postdoctoral fellow Peter D?rmann isolated controls the biosynthesis of galactolipids in plants - a substance that is abundant in all plant life.

"These lipids are the most abundant on earth," Benning said. "Everything that is green that we eat every day is filled with these. We eat a lot of them."

The lipids are the material that surrounds the plant's chloroplast. They form a complex matrix in which the plant, through photosynthesis, converts sunlight and water into energy and oxygen. But while lipids make up a significant part of the energy operation, it's the flashier parts of chloroplasts - the green chlorophyll and proteins - that have received most of the scientific attention.

That, Benning said, is largely because these lipids have been tough to study. While the lipids are abundant, the protein that produces the lipids is less so. It has resisted reproduction in the lab for years.

Benning and D?rmann started with a mutant variety of Arabidopsis - a weed, a small plant in the mustard family used worldwide as a model organism for basic and applied research in plant biology. This mutant is unable to make the galactolipid they studied. The result: The plant was small and pale for lack of photosynthesis.

They began the painstaking process of isolating and mapping the genetic sequence of the gene that produces the protein. Why they succeeded in generating enough genetic material to work with: They inserted the gene in E. coli bacteria, enabling the gene to produce the protein and reconstruct the biosynthetic pathway for the lipid outside of the plant world.

"The protein is in low abundance, so you just can't study it in the plant," Benning said. "But the galactolipids definitely are a part of the photosynthesis machinery - you can see that by looking at the mutant that cannot make the lipid.

"They've been ignored because they're hard to attack in a complex way, but we've opened the door enough to attack the problem and find out how important they really are."

The U.S. Department of Energy funded the research.

One possible benefit of learning about the role of the gene is developing herbicides which would prey on a plant's ability to conduct photosynthesis, Benning said.

The Science article comes on the heels of another last week by researchers in the MSU-Department of Energy Plant Research Laboratory. University Distinguished Professor Kenneth Keegstra, director of the plant lab, his associate Robyn Perrin and University Distinguished Professor Natasha Raikhel, who announced in the June 18 edition of Science that they have cloned one of the genes that creates part of a plant's cell wall.

Michigan State is a leader in The Arabidopsis Functional Genomics Consortium, a National Science Foundation-funded collaboration among several U.S. academic institutions working together to utilize and develop state-of-the-art technologies in Arabidopsis genomics.