Scientists discover new plant protein - important applications in energy crops

Scientists at Michigan State University have identified a new protein necessary for chloroplast development, which might lead to a whole new class of energy crops. The discovery allows researchers to design crops that grow oil in their leaves, stems or roots, instead of only in their seeds. The first lab trials with such engineered crops are already under way: a type of cold-tolerant root-crop (rutabaga) has been modified to become 'oily', growing biomass with the consistency of an avocado, full of easily extractable oil.

Chloroplasts, which are specialized compartments in plant cells, convert sunlight, carbon dioxide and water into sugars and oxygen ("fuel" for the plant) during photosynthesis. The newly discovered protein, trigalactosyldiacylglycerol 4, or TGD4, offers insight into how the process works.

Nobody knew how this mechanism worked before we described this protein. This protein directly affects photosynthesis and how plants create biomass (stems, leaves and stalks) and oils. - Christoph Benning, MSU professor of biochemistry and molecular biology

Professor Benning, the lead scientist working on the new protein, is a member of the Great Lakes Bioenergy Research Center, a partnership between MSU and the University of Wisconsin-Madison funded by the U.S. Department of Energy to conduct basic research aimed at solving some of the most complex problems in converting natural materials to energy.

The research, published in the August 2008 issue of journal The Plant Cell, shows how TGD4 is essential for the plant to make chloroplasts. Plants that don't have the protein die before they can develop beyond the embryonic stage.

Understanding how TGD4 works may allow scientists to create plants that would be used exclusively to produce biofuels, possibly making the process more cost-effective. Most plants that are used to produce oils – corn, soybeans and canola, for example – accumulate the oil in their seeds.

But the scientists found that if the TGD4 protein is malfunctioning, the plant then accumulates oil in its leaves. If the plant is storing oil in its leaves, there could be more oil per plant, which could make production of biofuels such as biodiesel more efficient:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: biodiesel :: vegetable oil :: chloroplast :: lipids :: biochemistry ::

Other members of the MSU research team are: Changcheng Xu, research assistant professor of biochemistry and molecular biology; Jilian Fan, research technician; and Adam Cornish, biochemistry undergraduate student at the time of the research and current graduate student. The research was funded by the Energy Department and the National Science Foundation. Professor Benning's research also is supported by the Michigan Agricultural Experiment Station.

Applying the knowledge
Professor Benning's team has started a project with genetically modified rutabagas, which should become squishy and oily. The scientists have inserted a gene called "wrinkled1" into the rutabagas that regulates the conversion of carbohydrates into oil.

The hope is that the gene will make the rutabagas produce oil rather than starch inside their bulbous roots, turning these cold-resistant root vegetables into a viable biofuel crop for Michigan. It will be at least six months before the scientists know whether the change works.

Plant oils are among the best potential sources of biofuel. They're rich in energy, easy to extract and convert. But they're inefficient in other ways. Most oilseed crops have relatively low yields per acre, and the seeds can be harvested only at certain times.

Benning hopes to produce better biofuel crops by developing plants that produce not only more oil, but oil that's more readily available.

We think we need to make oil in not just the seeds. If we could make it in the green tissues, like the leaves, stems or even underground tissues like roots or tubers, then we think we can make a lot more per land area. - Professor Christoph Benning

The newly discovered TGD4 protein helps the scientists in their research, as it plays a role in moving lipids, a group of organic compounds that includes fats and oils, around inside plant cells.

Lipids are the building blocks of the membranes surrounding and inside of chloroplasts, compartments inside the cell where plants convert solar energy into chemical energy - food, basically - during photosynthesis.

In this particular aspect of all of life - lipid synthesis of membranes - this is one of the biggest remaining questions. [Understanding the biochemical pathways that play a role in it] has implications for many, many aspects of practical plant biology, from increasing plant productivity to finding ways to generate new and useful products in plants. - John Browse, a professor of biochemistry and molecular plant sciences at Washington State University.

Benning and his colleagues hit on a promising side result, while researching the new protein. While plants will die without the TGD4 protein, a defective version of the protein will cause them to put lipids in the wrong places, causing plants to accumulate oil not only in their seeds, but in their leaves as well.

With current biofuel crops, corn and canola for example, "we have a very small portion of the biomass that goes to the seeds, and all the other stuff basically dries up, and nothing much happens with it". If plants could be made that produce oil throughout, "we could use that vegetative tissue, all that biomass that is going into making a plant", Benning said.

Schematic: chloroplast structure.

Picture: rutabaga, a cold-tolerant root crop.

References:
Changcheng Xu, Jilian Fan, Adam J. Cornish, and Christoph Benning, "Lipid Trafficking between the Endoplasmic Reticulum and the Plastid in Arabidopsis Requires the Extraplastidic TGD4 Protein", Plant Cell Advance Online Publication, Published on August 8, 2008; DOI: 10.1105/tpc.108.061176

MSU News: MSU’s discovery of plant protein holds promise for biofuel production - August 14, 2008.

Lansing State Journal: MSU biofuel research rooted in rutabagas - August 19, 2008.

Michigan State University: biofuel and bioenergy research.

Great Lakes Bioenergy Research Center.