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First tree joins genome club

September 14, 2006 By David Brill This article courtesy of Nature News.

Poplar sequence could help to turn trees into better fuels.

The first tree genome has been published. Armed with this information about the black cottonwood poplar (Populus trichocarpa), researchers hope they will be able to make the tree a better source of renewable energy.

"The ideal biofuels plant is very different from any currently available," says Toby Bradshaw, an expert on plant evolution at the University of Washington in Seattle. Now, he says, we have the ability to manipulate the biochemical pathways in a tree to produce a better fuel. "I think there's tremendous potential there."

The result, published in Science1, comes from a large international research team, funded mainly by the US Department of Energy (DoE). They chose the poplar because of its rapid growth rate and potential for use as a biofuel. Plus, it was expected to have a relatively small genome.

We have the genomes of everything from bacteria to humans (see 'Genome parade'), but this is only the third plant genome. The first two were Arabidopsis, a small flowering plant popular in plant biology, and rice, whose genome is being used to help produce tougher crops with larger yields.

The DoE announced in January plans to sequence the soybean (Glycine max), a major source of biodiesel. Different groups are looking at sequencing the eucalyptus and peach trees among others.

Better biomass

Biofuel production is not yet economically viable. Large amounts of land are needed for relatively low yields of ethanol fuel, which is squeezed from the plants' cellulose. The genome should help target efforts to improve this, says Gerald Tuskan of Oak Ridge National Laboratory, Tennessee, lead author of the report.

Researchers are aiming to use genetic techniques to make poplars grow fatter and with a smaller canopy, for example, so that more trees can be grown more quickly in a small space. And they would like to make the plants contain a higher proportion of cellulose to lignin. This makes them easier to convert into sugars and ethanol.

Results aren't expected immediately, however. "To have a completely domesticated organism producing biomass for ethanol, I think we're looking at 15 years," says Tuskan. "But we can make rapid incremental gains in the next 3 to 5 years."

China is already planting groves of genetically modified poplars that have been made to be resistant to insects. They aim to use poplars to stop growing deserts from encroaching on agricultural areas.

The sequencing effort identified more than 45,000 putative protein-coding genes in the Populus genome. The human genome, by comparison, is currently thought to contain about 20,000 genes.

The researchers compared the poplar genetic code to that of Arabidopsis, which shares a common ancestry with Populus. The researchers found that after their evolutionary paths diverged, the poplar duplicated its entire genome. This probably freed up the line to evolve, they say.

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  1. Tuskan G., et al. Science, 313. 1596 - 1604 (2006).


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