Plants form reproductive organs in a particular season of the year that is specific to each species, and these periods are referred to as reproductive periods 1, 2, 3, 4. Plants do not develop reproductive organs, such as flowers, during their initial growth. Instead, flowers are produced as new organs from pluripotent cells located in the meristems [5]. In perennial species, wherein individual plants reproduce over multiple years, new reproductive organs develop from the meristems each year [6]. During the nonreproductive period, meristems develop vegetative organs, such as leaves and stems. Therefore, meristems of the same individuals can be developmentally canalized as vegetative or reproductive, depending on the season. Season-specific developmental canalization is among the major characteristics of plants and is often referred to as the vegetative and reproductive phases 6, 7.

In many plant species, the timing of transitions between vegetative and reproductive phases is controlled by photoperiod and temperature regimes 8, 9, 10, 11. Plant groups that flower in spring require a combination of prolonged cold temperatures and long-day photoperiods after cold [12]. The vernalization response leads to the initiation of reproductive state that occurs when plants are exposed to long-term cold [13]. Vernalization in Arabidopsis relies on the epigenetic regulation of the floral repressor FLOWERING LOCUS C (FLC) 14, 15. Exposure to long-term cold induces mitotically stable repression of FLC through the action of the polycomb group factors that deposit histone H3 lysine-27 trimethylation (H3K27me3), a representative repressive histone modification, at the locus [16]. In A. thaliana, the repression of FLC is maintained until the end of reproduction, which also marks the end of the life cycle of the annual species 17, 18. In the perennial species A. halleri [19], FLC is released from stable repression toward the end of reproduction. The timing of full activation corresponds to the transition from reproductive to vegetative phases [20].

Under natural conditions, the temperature regimes in late autumn and early spring are similar, and plants are exposed to warm temperatures during the daytime and cold temperatures at night (Fig. 1). The seasonal patterns of FLC expression in perennial Arabidopsis suggest that the gene responds differently to autumn and spring temperature regimes [21]. In this mini-review, we summarize the recent progress in the understanding of FLC regulation in Arabidopsis, with special emphasis on how the locus is controlled under fluctuating temperatures and how the system responds differently to autumn and spring temperature regimes. Molecular dissections of A. thaliana FLC have improved our understanding of how the locus undergoes stable repression in autumn temperature regimes. The analyses of perennial Arabidopsis FLC have provided clues that help understand how the expression is robustly upregulated in the spring temperature regime. Hereafter, we refer to homologs in A. thaliana (annual) and A. halleri subsp. gemmifera (perennial) by adding At and Ahg prefixes to the gene names, respectively.