Photoperiodic control of FT-like gene ClFT initiates flowering in Chrysanthemum lavandulifolium

The FLOWERING LOCUS T (FT) gene plays crucial roles in regulating the transition from the vegetative phase to the reproductive phase. In this study, we isolated an FT homologous gene (denoted as ClFT) from Chrysanthemum lavandulifolium. The sequencing analysis indicated that the promoter of the ClFT gene contains many elements, such as light response, abscisic acid, drought-inducibility response and CIRCADIAN clock elements. The expression patterns of ClFT in different tissues/organs at different developmental stages and its responses to different photoperiods were observed. ClFT is expressed in all tested organs/tissues, with the highest expression level being observed in the leaves of plants with visible floral buds under the short day (SD) condition. Next, we studied the rhythmic expression of ClFT during different photoperiod treatments and found that the level of ClFT increases with additional hours of continuous dark. ClFT accumulates when the continuous dark period is 12 h, regardless of the duration of light period. The ectopic expression of the ClFT gene in wild type Arabidopsis (Col-0) results in early flowering, with high expression levels of endogenous LFY and SOC1 being observed in transgenic Arabidopsis. All results indicated that the ClFT gene plays an evolutionarily conserved role in promoting flowering in inductive short days in C. lavandulifolium and that this gene could serve as a vital target for the genetic manipulation of flowering time in chrysanthemums.