Identification and characterisation of a novel FT orthologous gene in London plane with a distinct expression response to environmental stimuli compared to PaFT

FLOWERING LOCUS T (FT) is a key integrator of environmental signals and internal cues, and codes for florigen-like activity which regulates the transition from vegetative to reproductive growth in flowering plants. Unlike annual plants, perennial tree species undergo several years of vegetative growth prior to the transition to the reproductive stage, as characterised by the ability to form flower buds. Thereafter, trees in temperate regions typically display an annual growth cycle involving distinct vegetative growth, flowering and dormancy stages. In London plane (Platanus acerifolia Willd.), a FT-like gene has previously been identified. Here, we report the isolation of a novel FT orthologous gene, PaFTL, and investigate the functions of PaFT and PaFTL through the analysis of expression profiles and transgenic phenotypes. PaFT displayed the highest levels of expression during tree dormancy, and similarly elevated expression levels were seen under conditions of low temperature and short days (LT/SD). In contrast, PaFTL transcripts were up-regulated during the floral transition phase, the early stages of inflorescence development and throughout the main flowering period, whereas expression levels were low and variable during dormancy and in response to LT/SD treatments. Ectopic expression of 35s::PaFTL in tobacco produced a phenotype similar to that with PaFT, namely, advanced floral initiation. Overall, the results suggest that PaFT and PaFTL have both conserved and diverse functions in floral initiation, floral development and dormancy regulation.