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DEVELOPMENT AND HORMONE ACTION

Ectopic Expression of Pumpkin Gibberellin Oxidases Alters Gibberellin Biosynthesis and Development of Transgenic Arabidopsis Plants¹

Institut für Pflanzenbiologie der Technischen Universität Braunschweig, D–38106 Braunschweig, Germany (A.R., T.L., M.J.P.L.); and National Institute of Floricultural Science, Tsukuba, Ibaraki 305–8519, Japan (T.N., M.K.)

Immature pumpkin (Cucurbita maxima) seeds contain gibberellin (GA) oxidases with unique catalytic properties resulting in GAs of unknown function for plant growth and development. Overexpression of pumpkin GA 7-oxidase (CmGA7ox) in Arabidopsis (Arabidopsis thaliana) resulted in seedlings with elongated roots, taller plants that flower earlier with only a little increase in bioactive GA₄ levels compared to control plants. In the same way, overexpression of the pumpkin GA 3-oxidase1 (CmGA3ox1) resulted in a GA overdose phenotype with increased levels of endogenous GA₄. This indicates that, in Arabidopsis, 7-oxidation and 3-oxidation are rate-limiting steps in GA plant hormone biosynthesis that control plant development. With an opposite effect, overexpression of pumpkin seed-specific GA 20-oxidase1 (CmGA20ox1) in Arabidopsis resulted in dwarfed plants that flower late with reduced levels of GA₄ and increased levels of physiological inactive GA₁₇ and GA₂₅ and unexpected GA₃₄ levels. Severe dwarfed plants were obtained by overexpression of the pumpkin GA 2-oxidase1 (CmGA2ox1) in Arabidopsis. This dramatic change in phenotype was accompanied by a considerable decrease in the levels of bioactive GA₄ and an increase in the corresponding inactivation product GA₃₄ in comparison to control plants. In this study, we demonstrate the potential of four pumpkin GA oxidase-encoding genes to modulate the GA plant hormone pool and alter plant stature and development.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Maria João Pimenta Lange (m.pimenta{at}tu-bs.de).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.073668.

^* Corresponding author; e-mail m.pimenta{at}tu-bs.de; fax 49–531–391–8180.

Received November 1, 2005; returned for revision November 30, 2005; accepted December 1, 2005.

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