Phalaenopsis orchid miniaturization by overexpression of OsGA2ox6, a rice GA2-oxidase gene.

Background: Phalaenopsis orchids are one of the most common potted orchids sold worldwide. Most Phalaenopsis cultivars have long inflorescences that cause shipping problems and increase handling costs. Miniaturization of Phalaenopsis orchids not only reduces overall production costs but also can expand the appeal of the orchids to a different group of consumers who prefer to keep flowers on desks or tabletops. Although some miniature Phalaenopsis plants can be obtained via hybridization or mutation, they are unpredictable and limited in variety. We therefore used the transgenic approach of overexpressing gibberellin 2-oxidase 6 (OsGA2ox6), a rice GA deactivation gene, to investigate its functional effect in miniaturizing Phalaenopsis and to create a stable miniaturization platform to facilitate a supply for the potential demands of the miniature flower market.

Results: A commercial moth orchid, Phalaenopsis Sogo Yukidian 'SPM313', was transformed with the plasmid vector Ubi:OsGA2ox6 and successfully overexpressed the OsGA2ox6 gene in planta. The transgenic lines displayed darker-green, shorter, and wider leaves, thicker roots and much shorter flower spikes (10 cm vs 33 cm) than the nontransgenic line with a normal flower size and blooming ability and are therefore an ideal miniaturized form of Phalaenopsis orchids.

Conclusions: We demonstrated that the ectopic expression of OsGA2ox6 can miniaturize Phalaenopsis Sogo Yukidian 'SPM313' while preserving its blooming ability, providing an alternative, useful method for miniaturizing Phalaenopsis species. This miniaturization by a transgenic approach can be further expanded by using GA2ox genes from different plant species or different gene variants, thereby expanding the technical platform for miniaturizing Phalaenopsis species to meet the potential demands of the miniature Phalaenopsis flower market.