Tree Research Could Lead to New Fuel Sources

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Scientists sequence the genome of a tree related to the poplar. Researchers think the finding could be a new milestone in the push for biofuels. Plant geneticist Gerald Tuskan discusses plans for using the newly discovered genetic information.


Up next this hour, an international team of scientists is reporting that they have sequenced the genome of the poplar tree. Now I know what you're thinking. Okay, that's exciting if I'm a tree farmer.

The consequences really could be staggering. It could one day mean a better source of paper and wood, of course, but also a place to store the excess carbon we generate from burning fossil fuels. Perhaps most importantly the trees could be a much better source of ethanol that the much-touted corn plant. Scientists say that by decoding the genome, they're able to figure out how to more efficiently change the wood cellulose into ethanol.

Joining me now to talk about the project is the lead researcher. Gerald Tuskan is a plant geneticist at the Environmental Sciences Division at Oak Ridge National Laboratory in Oak Ridge, Tennessee. Welcome to SCIENCE FRIDAY, Dr. Tuskan.

Dr. GERALD TUSKAN (Oak Ridge National Laboratory): It's great to be here.

FLATOW: This is so exciting that it made the cover of Science magazine.

Dr. TUSKAN: It did, yes. We were very honored to have the cover in this issue.

FLATOW: Why do you think it deserves the cover?

Dr. TUSKAN: Well, poplar black cottonwood is the first tree genome to be sequenced and annotated and assembled and as such, we've gotten a window into the evolution and function of genes unique to woody plants and perennial lifestyles. Arabidopsis and rice had their genomes sequenced and annotated and released publicly several years ago, but these are (unintelligible) annual plants. And for the first time we get to look into evolutionary history and function of genes related to large perennial woody organisms.

FLATOW: And possible use them as a source of ethanol. We're going to get into all of these. We have to go to a break Dr. Tuskan, but stay with us.

Dr. TUSKAN: Will do.

FLATOW: Everybody can stay with us. We'll be talking more about the sequencing of the gene for the first tree - the poplar tree - with Gerry Tuskan of the Oak Ridge National Laboratory. Stay with us. We'll be right back - take your questions. Don't go away.

(Soundbite of music)

FLATOW: You're listening to TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow. We're talking this hour with Gerald Tuskan, plant geneticist in the Environmental Sciences Division at the Oak Ridge National Laboratories in Oak Ridge, Tennessee. Our number, 1-800-989-8255. Dr. Tuskan is talking about his project, the first of its kind, to sequence a genome of a tree. We've had a couple of weedy kind of perennial plants but now we've got a tree sequence, and the fact that it's a poplar tree is very important because, Dr. Tuskan, that might help us solve our energy crisis, correct?

Dr. TUSKAN: That's right. Poplar is one of the model candidate species for dedicated energy crop development here in the U.S. It's a very fast growing plant and the biomass, or the cell wall, of poplar is uniquely suited for ethanol conversion, and so we're very excited about the opportunity to accelerate the domestication of poplar for the application to biofuels.

FLATOW: Could you bioengineer the plant to make it better suited for making ethanol?

Dr. TUSKAN: Most certainly. Poplar, whether it's here in the U.S. or in Asia or in Europe, really represent undomesticated wild organisms that because of evolutionary history have chemistries that are well suited for biochemical conversion to ethanol. But there's a lot that we could do to increase the efficiency of conversion or the cost efficiency of actually producing the biomass.

So we're looking at modifying the plant cell wall to increase the amount of cellulose that's deposited in the cell wall and we're also looking at increasing the harvestable yield off a given acre of land.

FLATOW: We haven't gotten to the point where you can successfully create ethanol out of trees and woody plants like that yet, have we?

Dr. TUSKAN: Well, we have in the lab and we have pilot scale conversion projects that have demonstrated that poplar in particular is one of the best feed stocks for the production of ethanol. The issue right now is to reduce the cost of that ethanol per gallon to make it more competitive with gasoline and increase the yield of ethanol per ton of biomass. And so we've demonstrated that it is feasible, that you do get high yielding high amounts of ethanol coming from lignocellulosic feed stocks, but we need to increase the yield of ethanol and reduce the price of that ethanol.

FLATOW: What makes it a better feed stock than, let's say, corn for making ethanol?

Dr. TUSKAN: Yeah, the current corn ethanol industry is based on starch produced mainly in the kernel and so there's a limit in how much starch you can produce per unit area of land. Alternatively, crops like hybrid poplar or switch grass are grown for energy and it's the lignocellulosic component of the cell wall.

So the productivity per unit of land is higher, because we use the sugar that's captured through photosynthesis into glucose and then is ultimately fixed into the cell wall in the form of cellulose and hemicellulose, so the amount of convertible sugar per unit area is higher with these lignocellulosic feed stocks.

FLATOW: Can you make it easier by genetically modifying the plant to get more energy out of it and to also make it easier in the laboratory to convert it into ethanol or into - or in the factory - to convert it into ethanol?

Dr. TUSKAN: Most certainly. The plant cell wall contains three major components - lignant, which is a polyphenolic compound, cellulose and hemicellulose, and cellulose and hemicellulose are carbohydrates and can be fermented into ethanol. The lignant, on the other hand, is like the glue that holds the whole thing together. And inherently poplar has about 30 percent lignant, and we believe we can reduce that effectively to less than 20 percent and not affect plant growth, but increase the amount of cellulose per dry weight and increase the deconstruction of the cell wall by having less lignant present in the modified cell wall.

FLATOW: And unlike corn, this plant will grow virtually anywhere, won't it?

Dr. TUSKAN: It has a very, very wide range of adaptability. It occurs naturally from the Arctic Circle in Alaska down to Baja, California as Populus trichocarpa, Black Cottonwood, but there are relatives of Populus that are adapted to almost the entire North American continent and, in fact, all of Europe and all of Asia.

There are large poplar planting programs going on right now in China. It's the largest planting effort in history and it's known as the Green Wall of China, and I can't tell you the number of acres, but it's a tremendous amount of poplar planting. It's all over the world, and so it's well adapted to many, many different sites. It's being deployed as hybrids of alternate species depending on what part of the world you're in.

FLATOW: One interesting aspect of this research that caught my attention was that the poplar trees can also be used for carbon sequestration. Tell us about what you can do with that and what that means.

Dr. TUSKAN: What we were able to discover once we sequenced and annotated the genome was that the biochemical pathway for cell wall biosynthesis above ground is different or independent of the biochemical pathway for cell wall biosynthesis below ground. So if we want to maximize the amount of ethanol per unit of area of land above ground we would favor cellulose and hemicellulose.

Below ground, if we want to increase the sequestration potential of the plant, we would favor lignant. So we believe that we can independently change the chemistry above and below ground and get biofuels from harvested portions above ground, and at the same time sequester carbon in long-term pools, such as lignant, in root systems below ground.

FLATOW: So when the plant breathes in carbon dioxide, it would be stored more efficiently in the root system?

Dr. TUSKAN: That's correct. For carbon sequestration you'd like that carbon, the CO2 that comes in to the plant through photosynthesis, to ultimately be stored in the form of lignant below ground.

FLATOW: So it's like two different plants you have going.

Dr. TUSKAN: It is like two different plants. It's one organism, one genotype, but we will upregulate cellulose biosynthesis above ground and then favor lignant biosynthesis below ground. And we didn't know that that was possible until we had sequenced the genome and annotated the biochemical pathways above and below ground and came to realize that there are independent genes that control the expression of cell walls above and below ground.

FLATOW: It sounds, Dr. Tuskan, just too good to be true.

Dr. TUSKAN: Well, it's true enough in the lab. We're in the process of trying to validate it in field conditions and continue to explore the improvement of cell walls above and below ground. So we'll see. I think in five years we'll have validated field trials. And if the validation holds up, I think in ten years we'll see domesticated poplar plantations producing energy out on the landscape.

FLATOW: That's great. We'll have to look forward to it. Thank you for taking time to talk with us.

Dr. TUSKAN: You're welcome. Thank you very much.

FLATOW: Good luck to you. Gerald Tuskan, a plant geneticist in the Environmental Sciences Division at Oak Ridge National Laboratory in Oak Ridge, Tennessee.

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