Functional analysis of FLOWERING LOCUS T orthologs from spring orchid (Cymbidium goeringii Rchb. f.) that regulates the vegetative to reproductive transition

The FLOWERING LOCUS T (FT) gene plays crucial roles in regulating the vegetative-to-reproductive phase transition. The FT-like gene of spring orchid (Cymbidium goeringii Rchb. f.), CgFT, was isolated and characterized. CgFT mRNA was detected in leaves, pseudobulb, and flowers. In flowers, CgFT was expressed more in young flower buds than in mature flowers, and was predominantly expressed in young ovary and sheath. Seasonal expression analysis in leaves of a three-year-old spring orchid showed that a large increase in transcription, which started on June 20 for CgFT. We propose that the increased transcription in the middle of June marks the beginning of flower induction in this species. The ectopic expression of CgFT in transgenic tobacco plants showed novel phenotypes by flowering earlier than wild-type plants. Further analysis of the flowering time-related genes indicated that the expression of LEAFY, APETALLA1, FRUITFULL and SEPALLATA1 were significantly upregulated in 35S::CgFT transgenic tobacco plants. These results indicated that CgFT is a putative FT homolog in spring orchid that regulates flower transition, similar to its homolog in Arabidopsis. This study provides the first information on the spring orchid floral gene to elucidate the regulation of the flowering transition in spring orchid.