The antiphasic regulatory module comprising CDF5 and its antisense RNA FLORE links the circadian clock to photoperiodic flowering

Summary Circadian rhythms of gene expression are generated by the combinatorial action of transcriptional and translational feedback loops as well as chromatin remodelling events. Recently, long noncoding RNA s (lnc RNA s) that are natural antisense transcripts ( NAT s) to transcripts encoding central oscillator components were proposed as modulators of core clock function in mammals ( Per ) and fungi ( frq / qrf ). Although oscillating lnc RNA s exist in plants, their functional characterization is at an initial stage. By screening an Arabidopsis thaliana lnc RNA custom‐made array we identified CDF 5 LONG NONCODING RNA ( FLORE ), a circadian‐regulated lnc RNA that is a NAT of CDF 5 . Quantitative real‐time RT ‐ PCR confirmed the circadian regulation of FLORE , whereas GUS ‐staining and flowering time evaluation were used to determine its biological function. FLORE and CDF 5 antiphasic expression reflects mutual inhibition in a similar way to frq / qrf . Moreover, whereas the CDF 5 protein delays flowering by directly repressing FT transcription, FLORE promotes it by repressing several CDF s ( CDF 1 , CDF 3 , CDF 5 ) and increasing FT transcript levels, indicating both cis and trans function. We propose that the CDF 5/ FLORE NAT pair constitutes an additional circadian regulatory module with conserved (mutual inhibition) and unique (function in trans ) features, able to fine‐tune its own circadian oscillation, and consequently, adjust the onset of flowering to favourable environmental conditions.