Genetically Engineering Trees That Self-Destruct

Poplar TreesScientists are now working with plant genomes to create trees that literally dissolve themselves into cellulose.

The research, designed to reduce the high costs of converting wood into cellulose, focuses on several novel and exceedingly strange methods to turn trees into autodigesters that literally ferment their own mass into biofuel feedstocks after cutting.

The intent is to reduce the enormous amount of energy (from coal, oil and gas) needed to grind, chop, boil or chemically treat wood to reduce it to its cellulosic components. With a genetically-engineered, or GM tree, such costs will be significantly reduced and the process toward biofuels made more environmentally friendly.  

One such process will use fungus genes to alter the genetic makeup of common biofuel trees like poplar. Poplar is the genus, and includes Chinese Aspen, Japanese Aspen, White Poplar, Grey Poplar, Common, Swedish, Trembling or Eurasian Aspen, Quaking or American Aspen, and Bigtooth Aspen. The latter two are native to North America. They flower and reproduce from seed.

The Department of Energy's Joint Genome Institute in California, under the direction of Eddy Rubin - the lead researcher in this field - has already isolated a number of fungi genes that could be spliced into poplar trees to make them self-fermenting. One is Clostridia. Another, Pichia stipitis, effectively ferments the xylose (wood sugar) found in hardwoods and agricultural residue like straw. This wood sugar is the essential feedstock for biofuel production, but the path to it is hampered by a tree's lignite structure - a sort of artificial plastic or polymer that binds the cellulose and is exceedingly difficult to disrupt.   

Rubin, whose pathway engineering technology is both superb and scary, has also suggested adding termite gut genes to trees so they would digest themselves. His research, published in The Nature Review (November 22, 2007) outlines more than 500 genes which could be used for the deconstruction of wood into biofuel-ready, plant-based feedstocks.

Another proposal, to use a chemical found in the gut of Asian longhorn beetle larva to break down tree fibers into cellulose and lignin, is rapidly gaining approval. According to Kelli Hoover, co-author and Penn State associate professor of entomology, and Scott Geib, lead author and Penn State doctoral student in entomology, these longhorn beetle larva have fungus in their intestines that can alter the chemical structure of lignin by adding or removing certain groups of molecules from the polymer chains that make up lignins.

This solution, which uses the fungus itself as part of the biofuel conversion process (but does not modify tree genes), is clearly preferable to Rubin's suggestions, which aim to produce GM trees with biofuel-relevant traits. These traits, which may include rapid growth, the ability to tolerate drought and pests, and optimal growth patterns in trunks and branches, also incorporate modifications to the basic structures of cell walls. While these modified cells clearly reduce the amount of fossil fuel needed for conversion, they also introduce tree characteristics for which Nature has had no opportunity to prepare.

The poplar species is the first tree genome sequence to be completely decoded, and so one might think it is ideally suited to such genetic manipulation. In fact, just the opposite is true. Because it reproduces via flowers and seeds, as noted above, the risks of genetic cross-contamination are exacerbated. Studies with transgenic or genetically modified (GM) trees show that gene-flow can be measured in miles, and the transgenic spread of characteristics from these flowering trees cannot be contained once released. Nor are terminator techniques - which aim to interfere with the reproductive cycle- a solution. Terminator techniques have consistently failed with food crops in the second generation. Trees, which spread pollen or seed for up to 100 years, will likely escape terminator parameters as quickly and exact even more damage on native ecosystems.

Agrofuesl the Road to DestructionThe Institute of Science in Society calls GM trees "the ultimate threat" to forest ecosystems. Terminator techniques, via "suicide genes" inserted into plant species (and obtained from Bacillus amylolquefaciens or Cornyebacterium diphtheria) also present other difficulties beyond cross-pollination - not the least of which is transgenic crossover of these bacteria to other plant species or even invertebrate, amphibian or mammalian populations. It may be a one-in-a-million chance, but thousands of GM trees up the odds that such a disease will arise and, once in the population, prove impossible to control.

Professor Steven Strauss of Oregon State University, who pioneered reproduction in poplar species, points out that when complete sterility is achieved (i.e., no more flowers or pollen), the resulting GM trees have to be propagated through grafts and the like, a time- and labor-intensive process not likely to lead to sufficient trees at a low-enough cost to make an impact on biofuel efforts.

Equally as important, somaclonal variation as a result of genetic manipulation creates extremely high levels of mutation and chromosomal instability, which could reverse sterility. In effect, you have "escapees", or reproductively active trees capable of cross-pollination whose genetic structure is seriously skewed. Since poplars already have a tendency to cross-pollinate with other species, the dangers are doubled.

Environmentalists all over the world are taking up the warning. As early as 1999, the World Wide Fund for Nature was reporting on over 100 trials of these GM trees which had taken place over the previous decade without adequate research into the possible effects and without appropriate controls to prevent cross-contamination. At least seventy trials in the U.S., and a handful more in Britain, opened a Pandora's Box of possibilities, from simple cross-species contamination - potentially up to distances of 400 miles - to the devastation of entire forest ecologies, right down to the beneficial insects that cooperatively manage forests without human intervention.

The European Union, which abandoned GM-tree research in 1999 when activists destroyed a plantation in Berkshire, has again approved GM tree efforts.

China is so far the only country to approve a GM forest tree as opposed to trees destined for biofuel (or biopharmaceuticals). In the U.S., debate rages, with proponents arguing that genetic engineering might be able to restore the Dutch Elm and other species lost to blight by inserting code that leaves them immune to their predators. Opponents cite trees' longevity, and ask not what will happen tomorrow, but what will happen in 40 or 100 years when these GM trees cross-pollinate with native stocks.  

No one can provide an answer. Until someone can, genetically modifying trees, or worse, modifying them to digest themselves, seems very bad policy and even more shortsighted science.   

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C Robb W. 429°

Wow! What a spectacularly bad idea. It's breathtaking in it's hubris. Why can't we trust to billions of years of evolution? We have been gifted an amazingly productive and fertile planet, one that solves it's own problems if left to it's own devices. It is the arrogance that we know best exemplified in the efforts discussed here that have thrown things out of balance.

As the planet has done for millenia, when a species gets out of control it is reduced to a mere fraction of it's fecund state if it is allowed to continue at all. Hmmm...... Can we guess what species is causing the problems now? We tinker at our peril.

Written in September 2008

Jeanne Roberts (anonymous)

We do, indeed, tinker at our peril, and I love your use of the word hubris, which - far more than scientific method - defines modern science's approach to the problems we face. You are spot on!

Written in September 2008

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