Increased gibberellin biosynthesis in transgenic trees promotes growth, biomass production and xylem fiber length

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In most tree-breeding programs worldwide, increasing the trees' growth rates and stem volumes and shortening their rotation times are important aims. Such trees would yield more biomass per unit area. Here we show that overexpressing a key regulatory gene in the biosynthesis of the plant hormone gibberellin (GA) in hybrid aspen (Populus tremula × P. tremuloides) improves growth rate and biomass. In addition, these transgenic trees have more numerous and longer xylem fibers than unmodified wild-type (wt) plants. Long fibers are desirable in the production of strong paper, but it has not as yet proved possible to influence this trait by traditional breeding techniques. We also show that GA has an antagonistic effect on root initiation, as the transgenic lines showed poorer rooting than the control plants when potted in soil. However, the negative effect on rooting efficiencies in the initial establishment of young plantlets in the growth chamber did not significantly affect root growth at later stages.

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Figure 1: Biosynthetic pathways converting
Figure 2: Northern analysis of 10 GA 20-oxidase overexpressing lines (numbers 1–15) and the control (C).
Figure 3: Enhanced growth of transgenic hybrid aspen.
Figure 4: Effects of GA 20-oxidase overexpression on (A) cell length (B) cell number per internode (C) number of xylem fibers, and (D) xylem fiber length.


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Thanks are due to Peter Hedden for the pAt2301 construct, Göran Sandberg and Björn Sundberg for helpful discussions, and Ingabritt Carlsson, Leif Lund, and Marie Nygren for technical assistance. The Swedish Natural Science Research Council (NFR), The Swedish Research Council for Agriculture Sciences (SJFR), Foundation for Strategic Research (SSF), and Jakob Wallenberg-Lars Erik Thunholms Stiftelse are acknowledged for financial support.

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Correspondence to Thomas Moritz.

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Eriksson, M., Israelsson, M., Olsson, O. et al. Increased gibberellin biosynthesis in transgenic trees promotes growth, biomass production and xylem fiber length. Nat Biotechnol 18, 784–788 (2000) doi:10.1038/77355

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