Photoperiodic control of flowering time

The rotation of the earth results in periodic changes in environmental factors such as daylength and temperature; the circadian clock is the endogenous mechanism responsible for day-length measurement, and allows plants to anticipate these fluctuations and modulate their developmental programs to maximize adaptation to those environmental cues. Flowering represents the transition from a vegetative to reproductive phase and is controlled by complex and highly regulated genetic pathways. In many plants, the time of flowering is strongly influenced by photoperiod, which synchronizes the floral transition with the favourable season of the year. Over the last decade, genetic approaches have aided the discovery of many signalling components involved in the photoperiod pathway and here, we highlight the significant progress made in identifying the molecular mechanisms that measure daylength and control flowering initiation in Arabidopsis, a long day (LD) plant, and in rice, a short day (SD) plant. Some components of the Arabidopsis regulatory network are conserved in other species, but the difference in the function of particular genes may contribute to the opposite photoperiodic flowering response observed between LD and SD plants. The specific regulatory mechanisms involved in controlling CONSTANS (CO) expression and stability by the circadian clock and the different photoreceptors will be described. In addition, the role of FLOWERING LOCUS T (FT), as part of the florigen, and several other light signalling and circadian-dependent components in photoperiodic flowering will be also discussed.