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GENETICS & APPLIED ECOLOGY
DNA: Code of the Wild
The Topic In-Depth: The Science of Forestry Genetics
by Sally Lehrman
March 2002
Inspired by the sequencing of the human genome, forest researchers would like to outline every gene of the pine and the poplar.
They are using molecular biology to pinpoint the instructions inside cells that contribute to wood that is strong and paper that is easy to pulp.
They are hunting down genes that could make trees resistant to pathogens, and testing whether they can use a gene gun to shoot foreign DNA through cell walls and still induce a healthy tree to grow.
Here is a sampling of major forestry biotechnology efforts in the United States:
Restoring the American Chestnut
Some forestry projects aim to use genetic engineering to clean up problems created by humans. One coalition is working to revive the American chestnut, a heritage tree once ubiquitous in Appalachian forests but now nearly gone except for scattered shrubs.
The culprit in this case is a fungus accidentally introduced into the United States a little more than a century ago by a Long Island nurseryman.
"It's a restoration project. It's kind of like going and cleaning up a toxic waste site," says William Powell, professor at the State University of New York College of Environmental Science and Forestry. "We want to go and clean up."
Powell, a molecular biologist, and his colleagues, Charles Maynard and Danny Fernando, aim to add one, two, maybe three genes that would enhance the chestnut's resistance to the fungus. They would then plant these engineered trees in orchards and parts of the Appalachian forest.
His group is testing its ability to add genes known to protect other plants by placing them on gold particles and shooting them into tree cells. As an alternate strategy for gene delivery, they may use bacteria to carry them in.
The work is funded primarily by New York State and the American Chestnut Foundation, whose members range from scientists to dairy farmers. Despite increasing attention to the potential risks of transgenics - such as overpowering the forest with "super trees" or harming beneficial organisms - the project has heard few complaints.
"Our research has taken a bit long because we've addressed their concerns," Powell says, explaining that foundation members have taken an active interest in the repercussions of developing transgenic chestnuts. "But it's a nice feedback loop."
For instance, when a Long Island dentist foundation member fretted about hurting insects that might chew on the chestnut leaves, the team of scientists altered the gene to make sure it would only be active in plant parts the bugs don't eat. The researchers also plan to check how soil organisms, as well as insects that feed off other parts of the tree, might be affected.
Powell isn't worried that the engineered trees will mix with wild relatives: the natural plants rarely grow old enough to flower.
Cleaning Toxic Sites
Researchers at the University of Georgia are testing the value of genetic engineering techniques in another type of restoration project: using trees to become environmental clean-up tools.
Clayton Rugh, working with Scott Merkle and Richard Meagher, has inserted a bacterial gene into cottonwood and a type of magnolia called yellow poplar. The alteration gives the trees an ability to convert mercury to a non-toxic form and grow despite high levels of the heavy metal. Rugh has continued his efforts at Michigan State University, where he is looking for ways to detoxify a wider range of pollutants using green ash, poplar, grasses and woody shrubs.
Flower Control
Steven Strauss, a geneticist at Oregon State University, hopes to give a boost to such genetic engineering projects by developing molecular switches that would control plant flowering.
If he is able to build a poplar that doesn't sexually reproduce, for example, ecologists and foresters could worry less about experimental trees out-crossing with their wild relatives and becoming weed-like "super trees."
"Flower control would be a big risk reduction factor," Strauss says.
Strauss' team has been working with six genes that trigger general stem tissue to make the structural and metabolic changes that produce a flower.
The group started by taking a close look at genes already identified in Arabidopsis, a small plant in the mustard family whose genome has been fully sequenced. Then they searched for comparable genes in the poplar tree, modified them and watched what happened. Now, working with poplars that won't cross with nearby tree species, the team is preparing to grow the plants in a one-acre plot outdoors.
The Pine Genome
North Carolina State University's Ron Sederoff is part of a team of scientists from five universities who apply the same techniques to trees as molecular biologists use on the human genome to map, sequence and understand gene expression. The National Science Foundation-sponsored project has identified 10,000 active pine genes and now is studying how and when the DNA does its work.
Sederoff is analyzing the pine genome in hopes of developing a faster-growing loblolly pine with a shorter, thicker stem and high-quality wood properties. His aim is to learn how to grow more trees on less land, making it possible to set aside natural forests from logging almost entirely.
"We want pine trees to be domesticated plants instead of wild plants, to grow trees like you would a crop," he says. "We should leave the forests alone."
One day about a decade ago, a high school student interning in Sederoff's lab found a natural alteration in a single gene that dramatically changed the composition of lignin. Lignin helps give wood its strength and must be extracted when making paper. Sederoff's team plans to use the discovery, which makes lignin easier to remove, to engineer ] trees that require fewer toxic chemicals to process into paper.
Tree Breeding
Despite the many advances in genetics, many foresters have decided to stick with traditional breeding practices for now, instead of directly changing genes - at least until ecologists can fully examine the impact of altered trees.
Wood chemist Hou-Min Chang, also at North Carolina State, is using genetic technology to take a close look at trees already created over three generations in a breeding program that began in 1956. He is working on tools that will enable foresters to take less than a teaspoonful of wood from a core sample of a young tree, then analyze traits such as lignin content, cellulose, and fiber length and coarseness. When molecular biologists find what they want, they can check for genes that seem to be associated with the best wood, paper or box wood quality.
Eventually, this information should contribute to more effective breeding programs to tailor short-rotation loblolly plantations toward a particular end product, he says - although the group plans to stop short of directly inserting or removing specific genes.
Chang, like many of his colleagues, wants to give ecologists a chance to understand the potential impact of transgenic trees before venturing to create them. Furthermore, he'd rather not trigger public anxiety over harming the natural forest.
"We are only looking at what Mother Nature has given us," Chang says. "We just don't feel the public is ready for genetic engineering. We want to implement it quickly and we don't want any social problems."
Additional original articles on genetics and applied ecology:
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