NFT1 involved in flowering initiation induced by heating temperature signaling for reproduction (Wilkie et al. 2008, arid areas(e.g Cyclamen, Pancratium and Bellevalia) require Hemming and Trevaskis 2011), a phenomenon known as'ver- high summer temperatures for flower transition within nalization. The MADS-box gene FLOWERING LOCUS C(FLC)is the bulb. No cold induction is required for Aoral development a key regulator of vernalization-induced Lowering in A thaliana and stalk elongation (Kamenetsky and Fritsch 2002, nd related species(Sheldon et al. 2008, Sheldon et al. 2009, Kamenetsky and Rabinowitch 2002, Flaishman and Wang et al. 2009b). FLC inhibits fowering by repressing the Kamenetsky 2006). However, limited information on the mo- genes that promote fowering such as FT and the lecular mechanisms that regulate Rower initiation in response SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1(SOC1) to temperature in bulbous geophytes is available to date ( Helliwell et al. 2006, Searle et al. 2006). Long durations of A high summer temperature signal is often used to advance cold temperatures suppress FLC transcription quantitatively, narcissus flowering. Chinese narcissus(Narcissus tazetta var. thereby allowing rapid flowering(Sheldon et al. 200 chinensis)is a plant from the Amaryllidaceae family that ex- A thaliana, FLC transcription is stably repressed by vernaliza. hibits summer dormancy. Its bulbs sprout in October to tion, and FLC expression remained low after the plants returned November(when soil temperature drops), grow throughout to warm conditions(Sheldon etal. 2000, Sheldonet al 2009). This the winter and flower in January to February. The above-ground effect provides a molecular 'memory of winter and allows rapid parts of the plants begin to senesce in late spring. Chinese fowering as temperature and daylength increase during spring. narcissus exhibits a 2 year juvenile phase. Florogenesis is The vernalization response in cereals is controlled by another initiated within large-sized bulbs during summer dormancy MADS-box gene, namely VERNALIZATION1(VRNI)(Trevaskis Timing of fower initiation in its dormant bulbs varies, depend et al. 2007). In contrast to FLC, VRNI promotes flowering, and its ing on where they were cultivated. Flower initiation occurs in transcript levels are low in plants that have not been vernalized. early June in Guangzhou, early July in Zhangzhou and late july in Exposure to cold temperatures increases VRNI transcript levels Shanghai(Zhong 1984, Li et al. 1987, Zhang and Yang 1987, Li quantitatively, thereby accelerating transition to reproductive et al. 2012). Noy-Porata et al. (2009) showed that foral initi- growth at the shoot apex, and also makes plants respond to ation and reproductive development in Galilee(N. tazetta) long days by de-repressing the long-day flowering-response path- cultivated in Israel is promoted by high temperature at an op- way in the leaves (Yan et al. 2003, von Zitzewitz et al. 2005, Sasani timum of 25C, whereas low temperatures(12C)inhibit for 号月已 et aL. 2009). In addition, the different roles of FT-like proteins in ogenesis completely. The foral transition in Chinese narcissus response to temperature, which regulates the reproductive tran- in response to environmental conditions and the molecular sition in some biennials and perennials, were revealed( Lifschitz mechanisms that regulate these responses remain unknown et al. 2006, Pin et al. 2010, Hsuet al. 2011). Two paralogs of the FT In this study, different temperature regimes were designed gene(BuFT1 and BvFT2)have evolved antagonistic functions in and different planting dates were employed for >3 years to biennial sugar beets(Beta vulgaris ssp. vulgaris). BvFT2 is func- determine the right inductive stimuli that will predict the re- tionally conserved with FT and is essential to fowering In con- productive development in the bulb of Chinese narcissus. The rast, BvFTI represses fowering, and its down-regulation is crucial reproductive organogenesis in 3-year-old bulbs and fowering for the vernalization response in beets. In the woody perennial percentage were assayed. Different storage temperature re- poplar(Populus spp ) the FLOWERING LOCUS T1(FT1) and gimes were also designed and performed on 2-year-old bulbs FLOWERING LOCUS T2( FT2) paralogs coordinate repeated to address the relationship between juvenile-adult phase ycles of vegetative and reproductive growth. Reproductive change and temperature. One Ft homolog, Narcissus onset is determined by FTi in response to winter temperatures, Flowering Locus T1(NFT1), was also isolated from Chinese nar- C29/=9E whereas vegetative growth and inhibition of bud set are pro- cissus. Its function was assayed to determine whether the genes moted by FT2 in response to warm temperatures and long days shown previously in A. thaliana also regulate flowering. This during the growing season(Hsu et aL. 2011). These advances sug. study showed that extended high temperature exposure not gest that the duplication or changes in FT genes contributed to only triggers the transition of the bulb shoot meristem(SM) the evolution of plant adaptation to environmental cues. Flower transition requires different temperature conditions, shortens the juvenile phase. In addition, NFTI was shown to depending on the ecological origin of the bulbous geophyte mediate flower transition in response to high temperature species(Halevy 1990, Flaishman and Kamenetsky 2006). es(eg. Lilium, Galtonia and Allium cepa)usually require low temperatures for fower differ Results entiation, such as vernalization in the winter annual model plant Arabidopsis Species with thermoperiodic cycles(such High storage temperature is essential to flower as Tulipa, Narcissus and Hyachinthus), from the Irano- initiation in Chinese narcissus ranian and Mediterranean regions, require relatively high The scanning electron microscopy(SEM)assay showed that temperatures for Lower differentiation inside the bulb, as well flower initiation occurred earlier in 3-year-old bulbs stored at as a period of low temperatures to allow foral stem elongation 30C compared with those under natural conditions( Fig. 1) and anthesis( Flaishman and Kamenetsky 2006). Species from Flower transition began in late july under natural conditions, Plant Cell Physiol. 54(2): 270-281(2013)doi: 10. 1093/pcp/pcs181 C The Author 2013. 271temperature signaling for reproduction (Wilkie et al. 2008, Hemming and Trevaskis 2011), a phenomenon known as ‘ver￾nalization’. The MADS-box gene FLOWERING LOCUS C (FLC) is a key regulator of vernalization-induced flowering in A. thaliana and related species (Sheldon et al. 2008, Sheldon et al. 2009, Wang et al. 2009b). FLC inhibits flowering by repressing the genes that promote flowering, such as FT and the SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) (Helliwell et al. 2006, Searle et al. 2006). Long durations of cold temperatures suppress FLC transcription quantitatively, thereby allowing rapid flowering (Sheldon et al. 2009). In A. thaliana, FLC transcription is stably repressed by vernaliza￾tion, and FLC expression remained low after the plants returned to warm conditions (Sheldonet al. 2000, Sheldonet al. 2009). This effect provides a molecular ‘memory’ of winter and allows rapid flowering as temperature and daylength increase during spring. The vernalization response in cereals is controlled by another MADS-box gene, namely VERNALIZATION1 (VRN1) (Trevaskis et al. 2007). In contrast to FLC, VRN1 promotes flowering, and its transcript levels are low in plants that have not been vernalized. Exposure to cold temperatures increases VRN1 transcript levels quantitatively, thereby accelerating transition to reproductive growth at the shoot apex, and also makes plants respond to long days by de-repressing the long-day flowering-response path￾way in the leaves (Yan et al. 2003, von Zitzewitz et al. 2005, Sasani et al. 2009). In addition, the different roles of FT-like proteins in response to temperature, which regulates the reproductive tran￾sition in some biennials and perennials, were revealed (Lifschitz et al. 2006, Pin et al. 2010, Hsu et al. 2011). Two paralogs of the FT gene (BvFT1 and BvFT2) have evolved antagonistic functions in biennial sugar beets (Beta vulgaris ssp. vulgaris). BvFT2 is func￾tionally conserved with FT and is essential to flowering. In con￾trast,BvFT1represses flowering, and itsdown-regulation is crucial for the vernalization response in beets. In the woody perennial poplar (Populus spp.), the FLOWERING LOCUS T1 (FT1) and FLOWERING LOCUS T2 (FT2) paralogs coordinate repeated cycles of vegetative and reproductive growth. Reproductive onset is determined by FT1 in response to winter temperatures, whereas vegetative growth and inhibition of bud set are pro￾moted by FT2 in response to warm temperatures and long days during the growing season (Hsu et al. 2011). These advances sug￾gest that the duplication or changes in FT genes contributed to the evolution of plant adaptation to environmental cues. Flower transition requires different temperature conditions, depending on the ecological origin of the bulbous geophyte species (Halevy 1990, Flaishman and Kamenetsky 2006). Species from temperate zones (e.g. Lilium, Galtonia and Allium cepa) usually require low temperatures for flower differ￾entiation, such as vernalization in the winter annual model plant Arabidopsis. Species with thermoperiodic cycles (such as Tulipa, Narcissus and Hyachinthus), from the Irano￾Turanian and Mediterranean regions, require relatively high temperatures for flower differentiation inside the bulb, as well as a period of low temperatures to allow floral stem elongation and anthesis (Flaishman and Kamenetsky 2006). Species from arid areas (e.g. Cyclamen, Pancratium and Bellevalia) require high summer temperatures for flower transition within the bulb. No cold induction is required for floral development and stalk elongation (Kamenetsky and Fritsch 2002, Kamenetsky and Rabinowitch 2002, Flaishman and Kamenetsky 2006). However, limited information on the mo￾lecular mechanisms that regulate flower initiation in response to temperature in bulbous geophytes is available to date. A high summer temperature signal is often used to advance narcissus flowering. Chinese narcissus (Narcissus tazetta var. chinensis) is a plant from the Amaryllidaceae family that ex￾hibits summer dormancy. Its bulbs sprout in October to November (when soil temperature drops), grow throughout the winter and flower in January to February. The above-ground parts of the plants begin to senesce in late spring. Chinese narcissus exhibits a 2 year juvenile phase. Florogenesis is initiated within large-sized bulbs during summer dormancy. Timing of flower initiation in its dormant bulbs varies, depend￾ing on where they were cultivated. Flower initiation occurs in early June in Guangzhou, early July in Zhangzhou and late July in Shanghai (Zhong 1984, Li et al. 1987, Zhang and Yang 1987, Li et al. 2012). Noy-Porata et al. (2009) showed that floral initi￾ation and reproductive development in ‘Galilee’ (N. tazetta) cultivated in Israel is promoted by high temperature at an op￾timum of 25C, whereas low temperatures (12C) inhibit flor￾ogenesis completely. The floral transition in Chinese narcissus in response to environmental conditions and the molecular mechanisms that regulate these responses remain unknown. In this study, different temperature regimes were designed and different planting dates were employed for >3 years to determine the right inductive stimuli that will predict the re￾productive development in the bulb of Chinese narcissus. The reproductive organogenesis in 3-year-old bulbs and flowering percentage were assayed. Different storage temperature re￾gimes were also designed and performed on 2-year-old bulbs to address the relationship between juvenile–adult phase change and temperature. One FT homolog, Narcissus Flowering Locus T1 (NFT1), was also isolated from Chinese nar￾cissus. Its function was assayed to determine whether the genes shown previously in A. thaliana also regulate flowering. This study showed that extended high temperature exposure not only triggers the transition of the bulb shoot meristem (SM) from the vegetative stage to the reproductive stage, but also shortens the juvenile phase. In addition, NFT1 was shown to mediate flower transition in response to high temperature. Results High storage temperature is essential to flower initiation in Chinese narcissus The scanning electron microscopy (SEM) assay showed that flower initiation occurred earlier in 3-year-old bulbs stored at 30C compared with those under natural conditions (Fig. 1). Flower transition began in late July under natural conditions, Plant Cell Physiol. 54(2): 270–281 (2013) doi:10.1093/pcp/pcs181 ! The Author 2013. 271 NFT1 involved in flowering initiation induced by heating at East China Normal University on June 3, 2013 http://pcp.oxfordjournals.org/ Downloaded from