Plant Physiol, July 2001, Vol. 126, pp. 965-972

Production of Dwarf Lettuce by Overexpressing a Pumpkin Gibberellin 20-Oxidase Gene

National Institute of Floricultural Science, 2-1 Fujimoto, Tsukuba, Ibaraki 305-8519, Japan (To.N., Ta.N., M.N., T.H., N.O., M.K.); National Institute of Vegetables and Tea Science, 360 Kusawa, Ano, Mie 514-2392, Japan (H.Y.); IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS41 9AF, United Kingdom (P.H.); Botanisches Institut und Botanischer Garten, TU Braunschweig, Mendelssohnstrasse 4, D-38106 Braunschweig (Brunswick), Germany (T.L.); and Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia (L.N.M.)

We investigated the effect of overexpressing a pumpkin gibberellin (GA) 20-oxidase gene encoding an enzyme that forms predominantly biologically inactive products on GA biosynthesis and plant morphology in transgenic lettuce (Lactuca sativa cv Vanguard) plants. Lettuce was transformed with the pumpkin GA 20-oxidase gene downstream of a strong constitutive promoter cassette (El2-35S-). The transgenic plants in which the pumpkin gene was detected by polymerase chain reaction were dwarfed in the T₂ generation, whereas transformants with a normal growth phenotype did not contain the transgene. The result of Southern-blot analysis showed that the transgene was integrated as a single copy; the plants segregated three dwarfs to one normal in the T₂ generation, indicating that the transgene was stable and dominant. The endogenous levels of GA₁ and GA₄ were reduced in the dwarfs, whereas large amounts of GA₁₇ and GA₂₅, which are inactive products of the pumpkin GA 20-oxidase, accumulated in these lines. These results indicate that a functional pumpkin GA 20-oxidase is expressed in the transgenic lettuce, resulting in a diversion of the normal pathway of GA biosynthesis to inactive products. Furthermore, this technique may be useful for controlling plant stature in other agricultural and horticultural species.