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Poplar genes being studied

June 4, 2003

pictureTrees have genes, just like humans and animals, and researchers at Oak Ridge National Laboratory are particularly interested in the genetic makeup of poplars (including various species of cottonwood and aspen).

ORNL scientists are working with colleagues at several research institutions to identify and manipulate the genes that affect the processing of carbon. They hope to enhance the ability of trees, either through hybrid breeding or genetic engineering, to store carbon for long periods of time in the underground root system and surrounding soils.

This effort at so-called carbon sequestration could be one of the options in the future to reduce the amount of carbon dioxide in the atmosphere. The level of CO2 has grown from about 280 parts per million to 365 ppm over the past 100 years.

Many scientists believe carbon dioxide and other "greenhouse gases'' may be contributing to global climate change.

"There's interest from a lot of agencies, including the Department of Energy, to look at technologies to slow or halt the rise in CO2 concentrations in the atmosphere,'' said Stan Wullschleger, a senior researcher in ORNL's environmental sciences division.

Some of those technologies may take decades to develop, but planting trees to store carbon is something that could be adopted fairly soon if the processes are well understood.

"We'll need to understand the genetic and molecular mechanisms that control carbon uptake and movement," said Wullschleger, a plant physiologist.

DOE is funding a three-year, $5.1 million research project to look at the possibility of using poplars to sequester carbon. ORNL is collaborating with the University of Florida, Oregon State University, University of Minnesota, the National Renewable Energy Laboratory and the U.S. Forest Service.

The poplar (scientific name Populus) is the first tree genome to be sequenced, and the genetic mapping is almost complete. But, as with the human genome, locating the genes is just a small part of understanding them.

"Having the sequence of all the genes is like having a phone book and trying to figure out how a city works,'' said Steve DiFazio, a molecular ecologist who's working on the project. "It gives you information, but you have to go in and query each one of those little points and figure out what they do. That's what this project is about. It's about getting a start on figuring out what the genes do that are associated with allocating carbon.''

Poplars have only about one-fifth the number of genes in humans, but identifying them and evaluating their functions are difficult tasks.

Scientists perform a range of experiments to determine the function of genes. They sometimes insert bits of DNA to knock out a specific gene and evaluate the effects of its absence.

DiFazio said he and others are developing a technology that will let scientists look at the "expression'' of thousands of genes simultaneously.

For the poplar project, researchers developed a "family" of 2,000 cottonwood seedlings, crossing a single female tree with a male to start. Such a base for genetic studies couldn't be done in humans and rarely is done with mice, but it's a big plus for researchers.

"Using that, we can very finely map the structure of the genome, and then we can look at traits like production of particular chemicals in the roots,'' DiFazio said. "Then we can figure out what markers are associated with those traits and get the actual gene that causes the production of those chemicals.''

Scientists are targeting genes that control hormone production in the trees because they know from decades of physiological studies that particular hormones control root development.

Once gene functions are identified and understood, scientists may be able to manipulate them to boost their capabilities. They are especially interesting in terrestrial systems that store certain forms of carbon - such as lignin - that are resistant to bacteria. Bacteria in soils typically work to break down carbon compounds and release the material back to the atmosphere as part of the natural cycle.

The ORNL team isn't doing the genetic engineering. Specialists at Oregon State are working that end of the project.

"They're probably the world leaders in transforming trees,'' DiFazio said.

Researchers are studying poplars for several reasons, but particularly because of their high growth rate and wide adaptation in North America, according to Tim Tschaplinski, another member of the research team.

The higher growth rate, via photosynthesis, boosts the potential for processing and storing carbon.

Tschaplinski said researchers also are looking at hydrid poplars that are drought resistant, which also would boost the potential for carbon storage.

Even if the research is successful, scientists acknowledge that using trees to sequester would just be a part of any solution to reduce carbon dioxide in the atmosphere. Also, to be of benefit, the tree plantings would need to be on a grand scale.

"We're talking about millions of acres,'' Wullschleger said. "We would hope to ultimately have a system where you could plant poplars for bio-energy sources (for production of ethanol and other fuels) that would displace fossil fuels and not result in any net increase in atmospheric CO2 concentrations. Then, the secondary benefit would be enhanced carbon sequestration.''

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