Molecular Ecology of Flowering Regulation Pathways: Flowering Regulation in the Natural Conditions

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Ambient temperature and photoperiod are known to be the major cues for plants to sense seasons. Contrary to the predictable nature of photoperiod along the calendar, the seasonal pattern of temperature only appears as a long-term trend. Therefore, plants require a molecular system that is sensitive to the long-term trend of temperature change but to the short-term fluctuations. Here we show that the Polycomb group (PcG) protein mediated transcription factor, FLOWERING LOCUS C (FLC), serves as a key mechanism for long-term integration of fluctuating ambient temperature in the perennial life cycle. We quantified FLC expression in leaves of naturally growing plants for a year at ca. one week intervals in a natural population of the perennial Arabidopsis halleri ssp. gemmifera. Contrary to what is known in the annual A. thaliana, reset of FLC repression occurs without passing generation in the perennial life cycle. FLC levels were highly associated with temperature regimes for past ca. 5 weeks throughout the year, and both suppression and increment of FLC were temperature-dependent. The seasonal pattern in FLC expression corresponded not only to the timing of vegetative-reproductive transition but also to the timing of the reverse transition. We concluded that FLC is not mealy a memory of winter but have more inclusive role as a quantitative tracer of long-term temperature fluctuation for seasonal phase control in the perennial life-cycle.