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2-Plants: Down in the forest, something stirs - GM trees are ontheir way



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TITLE:  Down in the forest, something stirs
        GM trees are on their way
SOURCE: The Economist
        http://www.economist.com/science/displaystory.cfm?story_id=3535741
DATE:   6 Jan 2005

------------------- archive: http://www.genet-info.org/ -------------------


Genetically modified arboriculture
Down in the forest, something stirs
GM trees are on their way

IN SEPTEMBER 2004, a group of scientists from around the world announced
that they had deciphered yet another genome. By and large, the world
shrugged and ignored them. The organism in question was neither cuddly
and furry, nor edible, nor dangerous, so no one cared. It was, in fact,
the black cottonwood, a species of poplar tree, and its was the first
arboreal genome to be unravelled. But perhaps the world should have paid
attention, because unravelling a genome is a step towards tinkering with
it. And that, in the end, could lead to genetically modified forests.

The black cottonwood was given the honour of being first tree because it
and its relatives are fast-growing and therefore important in forestry.
For some people, though, they do not grow fast enough. As America's
Department of Energy, which sponsored and led the cottonwood genome
project, puts it, the objective of the research was to provide insights
that will lead to "faster growing trees, trees that produce more biomass
for conversion to fuels, while also sequestering carbon from the
atmosphere." It might also lead to trees with "phytoremediation traits
that can be used to clean up hazardous waste sites."

The American Department of Energy's Joint Genome Institute has
information on its poplar genome research.

It is also pretty sure to lead to a lot of environmental protest--hence,
perhaps, the environmental emphasis of the energy department's mission
statement. Given the argument about genetically modified field-crops that
has taken place in some parts of the world, genetically modified forests
are likely to provoke an incandescent response. Soya, maize, cotton and
the like were already heavily modified for human use before
biotechnologists got their hands on them. One result is that they do not
do very well in the big, bad, competitive world outside the farmer's
field. But trees, even the sorts favoured by foresters, are wild
organisms. GM trees really might do well against their natural conspecifics.


The wood and the trees

Lofty mission statements aside, the principal commercial goals of
arboreal genome research are faster growth and more useful wood. The
advantage of the former is obvious: more timber more quickly. More useful
wood, in this context, mainly means wood that is more useful to the paper
industry, an enormous consumer of trees. In particular, this industry
wants to reduce the amount of lignin in the wood it uses.

Lignin is one of the structural elements in the walls of the cells of
which wood is composed. Paper is made from another of those elements,
cellulose. The lignin acts as a glue, binding the cellulose fibres
together, so an enormous amount of chemical and mechanical effort has to
be expended on removing it. The hope is that trees can be modified to
make less lignin, and more cellulose.

In a lucky break, it looks as though it might be possible to achieve both
goals simultaneously. A few years ago a group of researchers at Michigan
Technological University, led by Vincent Chiang, started the ball
rolling. They produced aspens, another species of poplar, that have 45%
less lignin and 15% more cellulose than their wild brethren, and grow
almost twice as fast, as well. The mixture the team achieved leaves the
combined mass of lignin and cellulose in the trunk more or less unchanged
and, contrary to the expectations of many critics, the resulting trees
are as strong as unmodified ones.

The trick Dr Chiang and his colleagues used was to suppress the activity
of one of the genes in the biochemical pathway that trees employ to make
lignin. They did this using so-called "antisense" technology.

Antisense technology depends on the fact that the message carried by a
gene is encoded in only one of the two strands of the famous DNA double
helix. Because of the precise pairing between the components of the two
strands, the other strand carries what can, in essence, be described as
an "antimessage". The message itself is copied into a single-stranded
messenger molecule which carries it to the protein-making parts of the
cell, where it is translated. But if this messenger meets a single-
stranded "antimessenger" before it arrives, the two will pair up. That
silences the messenger. Dr Chiang therefore inserted into his aspens a
gene that makes antimessengers to the lignin gene in question.

Wood can be improved in other ways, too. When it comes to papermaking,
long fibres of cellulose are preferable to short ones. Thomas Moritz, of
the Umea Plant Science Centre in Sweden, and his colleagues, have found
out how to make hybrid poplars that reflect this industrial preference.
In this case they did it by making a gene work overtime, rather than by
suppressing its activity. The gene they chose is involved in the
synthesis of a hormone called gibberellin and, once again, a side-effect
of the alteration was to cause the trees to grow faster.

How such genetically modified trees would fit in with the natural
environment is, of course, an important question--and it is important for
two reasons. The first is political. The row about GM crops shows that
people have to be persuaded that such technology will have no harmful
effects before they will permit its introduction. But there is also a
scientific reason. Trees have complex interactions with other species,
some of which are necessary for their healthy growth.

Claire Halpin, of Dundee University in Scotland, and her colleagues have
been looking into the question of environmental interactions using hybrid
poplars that contain antisense versions of two other genes for enzymes
involved in the production of lignin. The trees were grown for four years
at two sites in France and England, in order to see how they fitted in
with the local environment.


The trees and the bugs

The answer seems to be that they fitted in reasonably well. They grew
normally and had normal diplomatic relations with the local insects and
soil microbes. They also produced high-quality pulp.

A tree's interactions with soil microbes are often beneficial to it (the
microbes provide nutrients) so this is an important result. But insects
are frequently hostile, and some researchers are looking for ways to
protect trees from them. Lynette Grace of Forest Research in Rotorua, New
Zealand, for example, has taken an approach based on introducing the gene
for Bacillus thuringiensis (Bt) toxin, a natural insecticide. This gene
is already used to produce versions of crops such as cotton that do not
require the application of synthetic insecticides. Dr Grace and her
colleagues adapted it to the radiata pine, which is plagued by the
caterpillars of the painted apple moth.

Genetic modifications based on Bt are environmentally controversial. On
the one hand, they reduce the amount of pesticide needed. On the other,
there is a fear that the gene might "escape" from crops into wild plants
that form the foodstuffs of benign insects. In the case of trees it might
not even be necessary for the gene to jump species. GM trees, with
immunity to insect pests and faster growth rates than their unmodified
competitors, might simply spread by the normal processes of natural
selection. That really would be survival of the fittest.




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