Genetics: tree commons

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Genetics: tree commons
Genetics: tree commons

Tree Commodity Reveal

And again the world knows a little more: A female western balsam poplar named Nisqually 1 once had 45,555 genes during her lifetime when she became an unasked donor. Why does anyone care?


Nisqually 1, a female Populus trichocarpa poplar, once grew and thrived along the banks of the Northwestern river that gives it its name. From here she started an important journey - in pieces and in all directions. 39 laboratories from Finland to Florida had worked intensively on the innards of the wood and had finished the rough work almost two years ago. And now, under the leadership of Gerald Tuskan, all those involved are summarizing the result of their efforts: The genome of the poplar and thus of the first fully sequenced tree can be presented to the public.

From the plant kingdom, global gene collectors had only thoroughly sequenced two other species to date: the universal university laboratory weed Arabidopsis thaliana and mankind's most important food crop, rice. So why is the western balsam poplar number three?

There are several good reasons for poplar genetics, say Tuskan of Oak Ridge National Laboratory and his international colleagues. The most obvious: the poplar is a tree. And thus mostly part of a forest, and forests cover about 30 percent of the earth's surface, harbor enormous biodiversity under their roof, are decisive climate modulators and indispensable sources of raw materials. Specifically: An estimated third of all industrial processes use raw materials from the forest.

In order to become and remain a tree, every poplar needs tricks that herbs such as thale cress and rice can do without: Trees live much longer and survive very different seasons, to which they have to adapt flexibly; they rely on more stable, durable and expensive scaffolding structures made of wood, which their organism then has to produce in large quantities. The comparison to the Arabidopsis genes actually proves how balsam poplar and co master this challenge genetically: A significantly higher proportion of the 45,000 or so genome sections - half of which have no known function so far - encode for the synthesis apparatus of cellulose and lignin, the most important cell wall and wood components.

A comparatively large number of genes also help to keep the sheer size of a tree organism under control, such as the long transport processes and the sprawling rooting and sprouting processes, or are responsible for fighting diseases. Proportionally more genes in poplar than in Arabidopsis are also involved with processes of programmed cell death - perhaps, the scientists speculate, this has to do with the annual cyclic growth and decay of the tree splendor in adaptation to the seasons.

Populus trichocarpa is the largest poplar species in North America, but its genome, which is made up of around 480 million base pairs, deserves the label "compact" rather than "oversized": The human is a good six times as large, but only contains around half so many protein-coding genes. Other trees, such as the pine, pack nearly 50 times larger genomes into the cell nucleus than the western balsam poplar. A comparison with thale cress reveals that the poplar has taken it easy in the course of evolution since the two very different species developed separately from a common ancestor around 110 million years ago: the speed of gene modification through chromosome rearrangements, Since then, tandem gene duplications and nucleotide exchanges have increased by about six times in Arabidopsis.

Since the separation of herb and tree, the poplar has also gone through one of those total duplication events that are apparently typical for plants, according to the base pair analyzers working with Tuskan - the resulting second gene copy after such duplications offers enough play material for evolutionary improvements. The Populus genome subsequently lost many of the double genes, but also retained around 8000 of the fresh gene variants - probably not without reason.

And the future of western balsam poplar? It could look like an artificially accelerated present with a little help. Even today, the fast-growing wood - a germinating seed becomes a sexually mature tree after four to six years - is one of the favorites of wood users. Genetic engineering fine-tuning could bring the species an even brighter future, in which Populus trichocarpa becomes the main raw material for organically produced ethanol, say the genetic decipherers - for example, if genes are modified that control the internal cross-linking of the wood components. If microorganisms could break down cellulose, hemicellulose and lignin more easily and use it to ferment alcohol, then the genetically modified poplar wood would be the ideal basis for the production of bioethanol from greenery residues, which many of the industrially usable bacteria are still struggling with. This progress would certainly benefit the not outstanding profitability of large-scale ethanol production - and with it all of us between Finland and Florida.

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