Important gene controlling tree growth and development found

May 04, 2006

Scientists at the Umeå Plant Science Centre (UPSC) and the Swedish University of Agricultural Sciences (SLU) report today about a breakthrough in our understanding of how the growth and development of forest trees is controlled. In an article published in the international journal Science, they show that the FT gene that was previously shown to control the flowering time of annual plants, also controls tree flowering. With the help of this gene poplar trees can be stimulated to flower after a few weeks instead of after the normal 10-15 years. The scientists also show that the same gene not only controls the flowering time of trees, but also the timing of when the trees stop growing and set bud in the fall. That the same gene was involved in all these processes was highly unexpected.

The breakthrough for our understanding of the regulation of tree growth and development might revolutionize forest tree breeding and can lead to the development of new tree seedlings with a dramatically improved growth and also "tailor made" quality parameters suited for improved pulp and paper production, better construction materials and enhanced bioenergy production.

Trees are extremely important for life on earth. They are often a dominating part of the ecosystems and 30 per cent of the earths landmass is covered with forests. Trees produce many important products for mankind such as renewable fuel, cellulose for the pulp and paper industry and construction materials.

Compared to most other plants, trees display some key features. They are the latest flowering plants known ­ many trees do not form their first flower until they are 10-20 years old, sometimes even older! Trees also have the ability to cycle between growth and dormancy. This is a way to adopt to harsh winter conditions when the supply of water is low and the tree might be damaged from both drought and cold. The trees have adopted to these conditions by stopping growth and forming buds at the end of summer or early fall. Decidious trees also shed their leaves. The tree is now dormant and is as such much more resistant to drought and frost than if it had been actively growing.

It has been known for a long time that the trees sense that fall is coming by measuring the length of the day. When the days get shorter the trees "know" that it is time to stop growing and set buds, even if it is a very warm fall. The trees are known to display a "critical daylength". If the days get shorter than this critical daylength the tree responds with growth cessation and bud set. The further north the trees grow the more important it is to stop growing and form buds sufficiently early in late summer. This means that trees originating from different latitudes (different origins in the north to south direction, so called "provenances", display different critical daylengths. For instance, an aspen tree from the middle of Germany stops growing and sets buds when the days get shorter than 16 hours. Compare this with a tree from northern Sweden which stops growing and prepares for winter already when the days get shorter than 21 hours long. Trees from northern Norway can even display critical daylengths of 23 hours! This trait is genetically inherited and is kept if the tree is moved to a new climate.

How the trees control their flowering, and why trees set bud at a certain time in the fall have been important questions for the scientists to answer. This is for two reasons. These are important traits that "makes a tree into a tree". There is a considerable applied interest in these traits. If one can induce early tree flowering it should be possible to dramatically enhance the speed of forest tree breeding. Plant breeding has been extremely successful for the development of superior plant material for agriculture. It has, however, had a small impact on forestry. To a large extent this has been caused by the fact that a forest tree breeder has to wait for 10-20 years between each cross in his breeding program.

The poplar tree FT gene, controlling both the flowering time of trees and the time for growth cessation and bud set in the fall, has been identified by a research group led by professor Ove Nilsson at the Umeå Plant Science Centre (UPSC) and the Swedish University of Agricultural Sciences. The gene is very similar to the Arabidopsis FT gene, the gene that is producing the messenger molecule that controls the flowering of annual plants and that is considered to be the so called ³Florigen². Results concerning the Arabidopsis gene were published last year by the Nilsson group, also in Science. This finding was ranked by Science to belong to the third most important scientific discovery in 2005.

The scientists now show that the poplar FT gene is turned on before the tree starts flowering for the first time after 10-15 years. If the gene is activated prematurely in a transgenic tree, the tree can be stimulated to flower already in just a few weeks. After a few months completely normal flowers are formed.

It is also shown that the poplar FT gene is turned off in late summer just before the trees stop growing and set bud. By changing the activity of the FT gene the scientists could either prolong or shorten the growing season of the tree. They could also determine the mechanisms involved in growth cessation and bud set in the fall. This knowledge is vital if we want to adopt plants and trees to new climates.
-end-
The scientists that have been active in this study are: Henrik Böhlenius, Tao Huang, Laurence Charbonnel Campaa och Ove Nilsson from the Swedish University of Agricultural Sciences (SLU) in Umeå Sweden. Stefan Jansson from Umeå university, Sweden, Amy M. Brunner from the Virginia Polytechnic Institute and State University, USA, and Steven H. Strauss from Oregon State University, USA. The research has mainly been funded by the Swedish Foundation for Strategic Research (SSF).

Swedish Research Council

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