Poster: Hormone synthesis & metabolism

Abs # 471: Ectopic expression of Gibberellin 2-Oxidase from Spinach in Arabidopsis and Tobacco

Presenter:	Lee, Dong Ju , leedong@msu.edu
Authors	Lee, Dong Ju  (A)   Zeevaart, Jan A.D. (A)
Affiliations:	(A): Michigan State Univ.

Gibberellin 2-oxidases are a family of dioxygenases that inactivate gibberellins. A GA 2-oxidase, SoGA2ox3, specific for C₂₀-GAs was isolated from spinach. Recombinant SoGA2ox3 protein converted the C₂₀-GA precursors, GA₁₂ and GA₅₃, to GA₁₁₀ and GA₉₇, respectively. Thus, SoGA2ox3 competes with SoGA20ox for the common substrate, GA₅₃. To determine whether the ectopic expression of SoGA2ox3 gene would cause a GA-deficient phenotype, the 35S::SoGA2ox3 cDNA fusion construct was transformed into Arabidopsis and Nicotiana sylvestris (Ns). Introduction of the SoGA2ox3 gene causes a range of dwarf phenotypes. The severe transformants show dark-green, curled, and short leaves. We selected two homozygous dwarf lines with high expression of the SoGA2ox3 gene. Germination rate in transgenic lines 2 and 4 of Ns were much lower than in WT. However, treatment with GA₃ restored germination. WT plants started stem elongation after about 50 days in long day (LD) and reached a height of about 140 cm. By contrast, line 4 started stem elongation at 84 LD and reached a height of only 80 cm. Leaf size in line 4 was smaller than in WT plants. Root length in line 4 was 46% shorter then that in WT plants. But root growth was completely recovered by treatment with 3 mg/l GA₃, indicating that ectopic expression of SoGA2ox3 gene does not affect the GA responsiveness. Compared with GA contents in WT plants, the level of bioactive GA₁ was reduced by half, whereas GA₉₇ accumulated 3- to 4 times higher levels in line 4 than in WT plants. Thus, the dwarfism of line 4 results from the reduction of bioactive GA₁ contents. Supported by USDA grant No. 97-35304-4692 and DOE grant No. DE-FG02-91ER20021).