Induction of dwarfism in transgenic Solanum dulcamara by over-expression of a gibberellin 20-oxidase cDNA from pumpkin

The gibberellin (GA) 20-oxidase (CmGA20ox1) from immature pumpkin seed prod uces predominantly inactive tricarboxylic acid GAs. We expressed CmGA200x1 under the control of the CaMV 35S promoter in Solanum dulcamara to assess t he usefulness of this gene for reducing GA content in transgenic plants. Al l transgenic plants obtained were semi-dwarfs with smaller, deep-green leav es and highly pigmented stems compared to the wild-type. Such transformants flowered earlier than the wild-type plants and produced more fruit and mor e seeds per fruit. The transgene was efficiently expressed, producing high levels of CmGA200x1 transcript and protein. Furthermore, the concentration of GA(1) was reduced in leaves of the transformants to approximately 20% or less of that in the wild-type and to about 40% or less in stems. The conce ntrations of other 13-hydroxylated GAs were also reduced, except for the tr icarboxylic acid, GA(17), which accumulated in the transformants due to 18- hydroxylation of GA(25). By contrast, the concentrations of non-13-hydroxyl ated GAs, GA(4) and GA(34), were not consistently reduced, indicating that the effect of expressing the pumpkin gene may not be predictable. Transcrip t abundance for a native GA 20-oxidase gene was higher in the leaves and st ems of S. dulcamara transformed with the pumpkin gene than in wild-type, re flecting the feedback control of 20-oxidase gene expression that serves as a homeostatic mechanism for GAs.