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FT/ TFL1 family members have been known to be involved in the development and flowering in plants. In rose, Ro KSN, a TFL1 homologue, is a key regulator of flowering, whose absence causes continuous flowering. Our objectives are to functionally validate Ro KSN and to explore its mode of action in rose., We complemented Arabidopsis tfl1 mutants and ectopically expressed Ro KSN in a continuous-flowering (CF) rose. Using different protein interaction techniques, we studied Ro KSN interactions with Ro FD and Ro FT and possible competition., In Arabidopsis, Ro KSN complemented the tfl1 mutant by rescuing late flowering and indeterminate growth. In CF roses, the ectopic expression of Ro KSN led to the absence of flowering. Different branching patterns were observed and some transgenic plants had an increased number of leaflets per leaf. In these transgenic roses, floral activator transcripts decreased. Furthermore, Ro KSN was able to interact both with Ro FD and the floral activator, Ro FT. Protein interaction experiments revealed that Ro KSN and Ro FT could compete with Ro FD for repression and activation of blooming, respectively., We conclude that Ro KSN is a floral repressor and is also involved in the vegetative development of rose. Ro KSN forms a complex with Ro FD and could compete with Ro FT for repression of flowering. [ABSTRACT FROM AUTHOR]