Production of dwarf lettuce by overexpressing a pumpkin gibberellin 20-oxidase gene

We investigated the effect of overexpressing a pumpkin gibberellin (GA) 20- oxidase gene encoding an enzyme that forms predominantly biologically inact ive products on GA biosynthesis and plant morphology in transgenic lettuce (Lactuca sativa cv Vanguard) plants. Lettuce was transformed with the pumpk in GA 20-oxidase gene downstream of a strong constitutive promoter cassette (E12-35S-Omega). The transgenic plants in which the pumpkin gene was detec ted by polymerase chain reaction were dwarfed in the T-2 generation, wherea s transformants with a normal growth phenotype did not contain the transgen e. The result of Southern-blot analysis showed that the transgene was integ rated as a single copy; the plants segregated three dwarfs to one normal in the T-2 generation, indicating that the transgene was stable and dominant. The endogenous levels of GA(1) and GA(4) were reduced in the dwarfs, where as large amounts of GA(17) and GA(25), which are inactive products of the p umpkin GA 20-oxidase, accumulated in these lines. These results indicate th at a functional pumpkin GA 20-oxidase is expressed in the transgenic lettuc e, resulting in a diversion of the normal pathway of GA biosynthesis to ina ctive products. Furthermore, this technique may be useful for controlling p lant stature in other agricultural and horticultural species.