Forest scientists at Oregon State University have used genetic
modification to successfully manipulate the growth in height of trees,
showing that it's possible to create miniature trees that look similar to
normal trees -- but after several years of growth may range anywhere from 50
feet tall to a few inches.
This is a "proof of concept" that tree height can be readily
controlled by genetic engineering techniques. It opens the door to a wide
variety of new products for the ornamental and nursery industries, experts
say, if regulatory hurdles can be overcome -- a big "if."

"From a science perspective, this is a very interesting accomplishment
and there's no doubt it could be made to work," said Steven Strauss, a
professor of forest science at OSU.

"But further development may be precluded by social, legal and
regulatory obstacles," he said. "Clearly there would be concerns whether the
market for specialty tree products such as this would be strong enough to
make it worth the large investments of time, money and testing that current
regulation of genetically modified organisms would require, at least in the
U.S."

That aside, he said, it appears that with further research and
development programs, it would indeed be possible to create an elm tree --
which ordinarily would grow to 100 feet or more -- that is only five feet
tall at maturity, a charming addition that would fit nicely on a backyard
deck. Or a 30-foot version that might be a better fit on urban streets. Or,
in fact, just about any height in between. Other changes can also affect
foliage shapes or color in very attractive ways, and some might have value
in cleaning up environmental pollution.

In their studies, OSU scientists were able to create young poplar
trees, which grow rapidly and can reach a mature height of 150 feet or more,
that were anywhere from about 15 feet to a few inches tall after two years
of growth. The smallest of them could be difficult to even find, tiny little
"shrublets" among the flowers in the field site.

The manipulation of height growth was achieved by insertion of certain
genes, mostly taken from the model plant Arabidopsis, which inhibited the
action of a class of plant-specific hormones known as gibberellic acids.
These compounds are also used as sprays to control the size and fruiting of
orchard trees. In trees, the compounds promote the elongation of plant
cells -- when they are inhibited, the cells do not fully elongate, and
plants remain short and stocky.

"It's really interesting that these genes from Arabidopsis, which is a
small plant in the mustard family, have been conserved through 50-100
million years of evolution and can perform more or less the same function in
poplar trees," Strauss said. "The modified trees themselves look pretty much
normal, just a lot smaller, and a little more compact or bushy."

Altogether, the researchers used seven distinct kinds of genes and
more than 160 different types of genetic insertions to create about 600
genetically modified trees. All caused decreased signaling by gibberellic
acids. They were grown in the field with USDA approval, and assessed several
times for variation in size and appearance.

Other than reduced size, there appeared to be striking variation in
foliage color and leaf shape, some of which might have significant
ornamental value. Root development also appeared to be very strong, which
might provide increased stress tolerance and have value where extensive root
development is needed, such as in bioremediation of polluted soils or in
very windy, limited soil moisture situations.

From an environmental viewpoint, the researchers said, dwarfed trees
such as this are unlikely to be any kind of threat to spread, because they
would compete very poorly with normal or wild trees. In virtually all tree
species, low height is a disadvantage as trees compete for sunshine. Another
possible value, from that perspective, is that this trait might be used to
help control the spread of exotic and potentially invasive trees that are
commonly sold by nurseries.

The initial studies were done with poplar, Strauss said. Similar
results should be possible in any tree species, but are limited by the lack
of research into gene transfer methods for most ornamental and forest trees.
However, usable methods are already available for sweet gum, elm, black
locust and pines. The current successful modification with poplar could be
just "the tip of the iceberg," the researchers said in their report.

Dwarf trees and crop plants created with traditional cross-breeding or
horticultural techniques are already widely used in fruit trees, the
ornamental tree industry and agriculture.

The advances for cereals have been part of the "Green Revolution," in
which plants such as rice or wheat were created that directed less energy to
height growth and more to development of stout stems and plentiful seed. In
orchards, semi-dwarf fruit trees produce more fruit that is easier to
harvest. The improvements in cereal yields have been credited with
preventing the starvation of millions.

The findings were recently published in the journal Landscape Plant
News.


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