Horticultural characterization of a tetraploid transgenic plant of Tricyrtis sp. Carrying the gibberellin 2-oxidase gene

Abstract

The gibberellin 2-oxidase catalyzes the bioactive gibberellins or their immediate precursors to inactive forms. We have previously produced transgenic plants of the liliaceous plant Tricyrtis sp. containing the GA2ox gene from the linderniaceous plant Torenia fournieri. These transgenic plants showed dwarf phenotypes as expected but unfortunately had no flowers or only small, unopened flowers. Recently, one newly produced transgenic line (G2-55) formed fully opened flowers. G2-55 showed a moderately dwarf phenotype and the shoot length decreased to 63.4% of that of the control, non-transgenic plants. No significant differences in the number of flowers per shoot and in the flower size were observed between G2-55 and the control. Flow cytometry analysis and chromosome observation showed that G2-55 was tetraploid (2n=4x=52), whereas the other transgenic lines producing no or only small flowers were diploid (2n=2x=26) as the mother plant. Pollen fertility of G2-55 was 81.2% as determined by acetocarmine staining. The tetraploidy in G2-55 might be resulted from somaclonal variation of embryogenic calluses used as a target material for Agrobacterium-mediated transformation. The tetraploid transgenic plant G2-55 may be useable not only directly as a potted plant, but also as a material for further breeding of Tricyrtis spp.