Gibberellins (GAs) are the plant hormones that control many aspects of plant growth and development, including stem elongation.
Genes encoding enzymes related to the GA biosynthetic and metabolic pathway have been isolated and characterized in many plant
species. Gibberellin 2-oxidase (GA2ox) catalyzes bioactive GAs or their immediate precursors to inactive forms; therefore,
playing a direct role in determining the levels of bioactive GAs. In the present study, we produced transgenic plants of the
liliaceous monocotyledon Tricyrtis sp. overexpressing the GA2ox gene from the linderniaceous dicotyledon Torenia fournieri
(TfGA2ox2). All six transgenic plants exhibited dwarf phenotypes, and they could be classified into two classes according
to the degree of dwarfism: three plants were moderately dwarf and three were severely dwarf. All of the transgenic plants
had small or no flowers, and smaller, rounder and darker green leaves. Quantitative real-time reverse transcription-polymerase
chain reaction (PCR) analysis showed that the TfGA2ox2 expression level generally correlated with the degree of dwarfism.
The endogenous levels of bioactive GAs, GA1 and GA4, largely decreased in transgenic plants as shown by liquid chromatography-mass
spectrometry (LC-MS) analysis, and the level also correlated with the degree of dwarfism. Exogenous treatment of transgenic
plants with gibberellic acid (GA3) resulted in an increased shoot length, indicating that the GA signaling pathway might normally
function in transgenic plants. Thus, morphological changes in transgenic plants may result from a decrease in the endogenous
levels of bioactive GAs. Finally, a possibility of molecular breeding for plant form alteration in liliaceous ornamental plants
by genetically engineering the GA metabolic pathway is discussed.