Promotion Of Flowering Research Articles

The sugar transporter SWEET10 acts downstream of FLOWERING LOCUS T during floral transition of Arabidopsis thaliana

BackgroundFloral transition initiates reproductive development of plants and occurs in response to environmental and endogenous signals. In Arabidopsis thaliana, this process is accelerated by several environmental cues, including exposure to long days. The photoperiod-dependent promotion of flowering involves the transcriptional induction of FLOWERING LOCUS T (FT) in the phloem of the leaf. FT encodes a mobile protein that is transported from the leaves to the shoot apical meristem, where it forms part of a regulatory complex that induces flowering. Whether FT also has biological functions in leaves of wild-type plants remains unclear.ResultsIn order to address this issue, we first studied the leaf transcriptomic changes associated with FT overexpression in the companion cells of the phloem. We found that FT induces the transcription of SWEET10, which encodes a bidirectional sucrose transporter, specifically in the leaf veins. Moreover, SWEET10 is transcriptionally activated by long photoperiods, and this activation depends on FT and one of its earliest target genes SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1). The ectopic expression of SWEET10 causes early flowering and leads to higher levels of transcription of flowering-time related genes in the shoot apex.ConclusionsCollectively, our results suggest that the FT-signaling pathway activates the transcription of a sucrose uptake/efflux carrier during floral transition, indicating that it alters the metabolism of flowering plants as well as reprogramming the transcription of floral regulators in the shoot meristem.

The CYCLIN-DEPENDENT KINASE Module of the Mediator Complex Promotes Flowering and Reproductive Development in Pea.

Control of flowering time has been a major focus of comparative genetic analyses in plant development. This study reports on a forward genetic approach to define previously uncharacterized components of flowering control pathways in the long-day legume, pea (Pisum sativum). We isolated two complementation groups of late-flowering mutants in pea that define two uncharacterized loci, LATE BLOOMER3 (LATE3) and LATE4, and describe their diverse effects on vegetative and reproductive development. A map-based comparative approach was employed to identify the underlying genes for both loci, revealing that that LATE3 and LATE4 are orthologs of CYCLIN DEPENDENT KINASE8 (CDK8) and CYCLIN C1 (CYCC1), components of the CDK8 kinase module of the Mediator complex, which is a deeply conserved regulator of transcription in eukaryotes. We confirm the genetic and physical interaction of LATE3 and LATE4 and show that they contribute to the transcriptional regulation of key flowering genes, including the induction of the florigen gene FTa1 and repression of the floral repressor LF Our results establish the conserved importance of the CDK8 module in plants and provide evidence for the function of CYCLIN C1 orthologs in the promotion of flowering and the maintenance of normal reproductive development.

Regulatory function of EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1 in the floral transition of Arabidopsis thaliana

The plasma membrane- and endoplasmic reticulum-localized proteins encoded by the EARLI1 (EARLY ARABIDOPSIS ALUMINUM INDUCED 1) subfamily of genes contain a signal peptide, a proline-rich domain and an eight-cysteine motif. We previously showed that knockdown of EARLI1 subfamily genes in the late-flowering background of Col-FRI-Sf2 accelerates flowering time, suggesting that EARLI1 genes participate in maintenance of vegetative growth and prevention of premature reproductive growth. We show here that ELHyPRP1 (EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1, AT4G12490), a member of this subfamily, is induced by environmental factors such as cold and long-day photoperiod. Detailed analyses with RNA interference and overexpressing lines demonstrated that modulation of ELHyPRP1 can affect the expression of photoperiod, vernalization, gibberellin, age, and autonomous flowering pathway genes. When ELHyPRP1 and other EARLI1 subfamily genes were silenced by RNA interference, most genes participating in the promotion of flowering were activated, while suppressors of the floral transition were repressed. Downregulation of ELHyPRP1 leads to increased expression of the flowering time genes FT and SOC1, and enhanced circadian expression patterns of genes associated with the promotion of the floral transition. Together with the silencing of ELHyPRP1, the flowering repressor FLC and the GA signalling repressor RGA were inhibited. ELHyPRP1 transgenic tobacco plants displayed late-flowering phenotypes and their flowering time was remarkably delayed in comparison to the wild-type Qinyan 95 tobacco plants grown under long-day photoperiod. These results indicate that ELHyPRP1 may be involved in balancing biomass accumulation and seed proliferation.

Phototropin is partly involved in blue-light-mediated stem elongation, flower initiation, and leaf expansion: A comparison of phenotypic responses between wild Arabidopsis and its phototropin mutants

Our previous study on bedding plants indicated that blue light in association with low phytochrome activity, relative to red light, can promote elongation growth as one of the shade-avoidance responses. We hypothesized that phototropin is involved in the blue light promotion effects. To test the hypothesis, plant growth and morphology were examined in wild Arabidopsis (Col-0), and its three phototropin-deficient mutants (phot1, phot2, and phot1phot2) under four light quality treatments: (1) R, pure red light (660 nm); (2) B, pure blue light (455 nm); (3) BR, unpure blue light created by mixing B with low-level (6 %) R; and (4) BRF, unpure blue light created by adding low-level far-red light (735 nm) to BR with red/far-red ≈ 1. Continuous (24-h) light-emitting diode lighting with 100 μmol m−2·s−1 photosynthetic photon flux density, and an air temperature of ≈ 23 ℃ were used with the above treatments. The calculated phytochrome photoequilibrium, an indicator of phytochrome activity, was 0.89, 0.69, 0.50, and 0.60 for R, BR, B, and BRF, respectively. After 20 days of light treatments, for the wild-type plants, B or BRF, compared to R or BR, promoted stem elongation, plant flowering, and leaf expansion, showing typical shade-avoidance responses. However, for the phototropin mutants, the promotion effects of B or BRF, relative to R or BR, on the above plant traits were reduced. In the absence of the phototropin(s), plants had reduced stem elongation and delayed flower initiation under B or BRF rather than R or BR, or reduced leaf expansion to a larger degree under B or BRF than R or BR. Our results suggest that phototropin is partly involved in the promotion of stem elongation, plant flowering, and leaf expansion mediated by blue light in association with low phytochrome activity.

Molecular Basis of Flower Formation in Apple Caused by Defoliation and Gibberellins

Adequate flower formation limits dependable apple (Malus ×domestica) production and is a major challenge for apple industries around the world. ‘Honeycrisp’ is a high value apple cultivar, but consistent flowering is difficult to achieve. Apple flower formation is affected by factors including defoliation, girdling, and gibberellin (GA4+7) and 1-naphthaleneacetic acid (NAA) applications. However, the molecular mechanisms that regulate the effects of these factors are not well understood. We studied the effect of local spur defoliation, GA4+7 and NAA applications on ‘Honeycrisp’ flower formation. Furthermore, we investigated the effect of local defoliation and local GA4+7 application on the transcript levels of two major flower formation genes in the meristems of apple spurs. The floral inhibition gene terminal flower1-1 (MdTFL1-1) and floral promoting genes flowering locus T (MdFT1 and MdFT 2) of apple. Local application of GA4+7 and defoliation treatments inhibited flower formation, but NAA applications were without effect. Defoliation treatments were accompanied by a significant reduction in MdFT1, 2 transcript levels compared with controls early in the growing season. Conversely, GA4+7 application was accompanied by a significant increase in MdTFL1-1 transcripts compared with controls throughout the growing season. These results indicate that GA4+7 inhibits flower formation by upregulating the inhibitory MdTFL1-1, and defoliation acts by downregulating transcript levels of MdFT1, 2 early in the growing season. We also provide evidence that defoliated bourse buds may receive flowering promotion signals from other parts of the tree in the absence of their local leaves.

Stimulatory Effect of Silver Nanoparticles on the Growth and Flowering of Potted Oriental Lilies

Nanoparticles exhibit unique biological activities and may serve as novel plant growth stimulators. This research consisted of a two-year pot experiment designed to find out if silver nanoparticles (AgNPs) might be used in the cultivation of Oriental lilies. In the first year, we evaluated the effects of various concentrations of AgNPs (0, 25, 50, 100, and 150 ppm) and their application methods (pre-planting bulb soaks, foliar sprays, and substrate drenches) on the growth and flowering of Lilium cv. Mona Lisa. In the second year, we evaluated the effects of soaking the bulbs of cv. Little John in the same concentration of AgNP solution on plant morphological features, leaf content of photosynthetic pigments, basic macronutrients, and complex biomolecules with the use of the Fourier-transform infrared spectroscopy (FTIR). Soaking the bulbs in a nanoparticle solution turned out to be the most effective strategy for growth and flowering promotion. AgNPs stimulated plant growth, as manifested by enhanced accumulation of leaf and bulb biomass and accelerated flowering. Moreover, plants treated with silver nanoparticles showed higher leaf greenness index, formed more flowers, and flowered longer. At 100 ppm AgNPs, the leaves accumulated the highest content of chlorophyll a, chlorophyll b, and carotenoids, and were the richest in potassium, calcium, and sulfur. The FTIR spectra did not show any changes in absorbance intensity and chemical composition in the leaves from AgNP-treated bulbs.

Blue radiation attenuates the effects of the red to far-red ratio on extension growth but not on flowering

Phytochromes, which primarily absorb red (R; 600–700 nm) and far-red (FR; 700–800 nm) radiation, and cryptochromes, which primarily absorb blue (B; 400–500 nm) radiation, coordinately control plant morphological and developmental traits, including extension growth and flowering. However, the effects of B and the R:FR on plant responses have usually been investigated independently, and how they interact to regulate plant traits has not been well characterized. We postulated that B radiation would attenuate the effect of the R:FR on extension growth, and with FR, promote flowering. We grew seedlings of petunia (Petunia ×hybrida), geranium (Pelargonium ×hortorum), and coleus (Solenostemon scutellariodes) at 20 °C under six sole-source light-emitting diode treatments with an 18-h photoperiod. The treatments delivered the following photon flux densities (subscript in μmol·m−2·s−1) of B (peak = 447 nm), R (peak = 660 nm), and/or FR radiation (peak = 731 nm): B80R80, B80R80FR10, B80R80FR80, R160, R160FR20, and R160FR160. Seedlings were then transplanted and subsequently grown in a common greenhouse environment at 20 °C with a 16-h photoperiod. Seedling height of all species increased linearly with additions of FR [as the R:FR or estimated phytochrome photoequilibrium (PPE) decreased]. When R was partly substituted with B radiation (B80R80), seedling height of all species also increased linearly with decreasing PPE, but substantially less (55–86%) than under R160. In all species, shoot dry weight decreased linearly with increasing PPE similarly under R160 and B80R80. In the long-day plant petunia, decreasing the PPE promoted subsequent flowering by 7–11 d, regardless of the presence of B radiation. We conclude that a moderately high B photon flux density attenuates the effects of the R:FR on extension growth but has no apparent effect on the FR promotion of flowering in a long-day plant. This suggests that cryptochrome-mediated B signaling dominates phytochrome-mediated FR signaling in the regulation of extension growth, but not flowering.

The flowering hormone florigen accelerates secondary cell wall biogenesis to harmonize vascular maturation with reproductive development

Florigen, a proteinaceous hormone, functions as a universal long-range promoter of flowering and concurrently as a generic growth-attenuating hormone across leaf and stem meristems. In flowering plants, the transition from the vegetative phase to the reproductive phase entails the orchestration of new growth coordinates and a global redistribution of resources, signals, and mechanical loads among organs. However, the ultimate cellular processes governing the adaptation of the shoot system to reproduction remain unknown. We hypothesized that if the mechanism for floral induction is universal, then the cellular metabolic mechanisms underlying the conditioning of the shoot system for reproduction would also be universal and may be best regulated by florigen itself. To understand the cellular basis for the vegetative functions of florigen, we explored the radial expansion of tomato stems. RNA-Seq and complementary genetic and histological studies revealed that florigen of endogenous, mobile, or induced origins accelerates the transcription network navigating secondary cell wall biogenesis as a unit, promoting vascular maturation and thereby adapting the shoot system to the developmental needs of the ensuing reproductive phase it had originally set into motion. We then demonstrated that a remarkably stable and broadly distributed florigen promotes MADS and MIF genes, which in turn regulate the rate of vascular maturation and radial expansion of stems irrespective of flowering or florigen level. The dual acceleration of flowering and vascular maturation by florigen provides a paradigm for coordinated regulation of independent global developmental programs.

Fine-tuning of the flowering time control in winter barley: the importance of HvOS2 and HvVRN2 in non-inductive conditions

BackgroundIn winter barley plants, vernalization and photoperiod cues have to be integrated to promote flowering. Plant development and expression of different flowering promoter (HvVRN1, HvCO2, PPD-H1, HvFT1, HvFT3) and repressor (HvVRN2, HvCO9 and HvOS2) genes were evaluated in two winter barley varieties under: (1) natural increasing photoperiod, without vernalization, and (2) under short day conditions in three insufficient vernalization treatments. These challenging conditions were chosen to capture non-optimal and natural responses, representative of those experienced in the Mediterranean area.ResultsIn absence of vernalization and under increasing photoperiods, HvVRN2 expression increased with day-length, mainly between 12 and 13 h photoperiods in our latitudes. The flowering promoter gene in short days, HvFT3, was only expressed after receiving induction of cold or plant age, which was associated with low transcript levels of HvVRN2 and HvOS2. Under the sub-optimal conditions here described, great differences in development were found between the two winter barley varieties used in the study. Delayed development in ‘Barberousse’ was associated with increased expression levels of HvOS2. Novel variation for HvCO9 and HvOS2 is reported and might explain such differences.ConclusionsThe balance between the expression of flowering promoters and repressor genes regulates the promotion towards flowering or the maintenance of the vegetative state. HvOS2, an ortholog of FLC, appears as a strong candidate to mediate in the vernalization response of barley. Natural variation found would help to exploit the plasticity in development to obtain better-adapted varieties for current and future climate conditions.

Organization of Mobile Flowering Signals in ICCV 96029 Chickpea Cultivar

ICCV 96029 is the earliest flowering chickpea cultivar. We analyzed the model of the gene network controlling floral transition and hypothesized that this chickpea cultivar is significantly different from other legumes in organization of mobile flowering signals related to the expression of the FT (FLOWERING LOCUS T) gene paralogs. Unlike pea and other legumes, that according to previously obtained data could demonstrate cross-regulation between FT-like genes and different nature of the associated flowering signals, the simulation results for chickpea suggest that the FT paralogs play additive roles in the promotion of flowering.

Promotion of Flowering by Bulb-type Three-color Mixed LEDs in <i>Gypsophila paniculata</i> L.

Promotion of Flowering by Bulb-type Three-color Mixed LEDs in <i>Gypsophila paniculata</i> L.

Regulation of flowering by green light depends on its photon flux density and involves cryptochromes.

Photoperiodic lighting can promote flowering of long-day plants (LDPs) and inhibit flowering of short-day plants (SDPs). Red (R) and far-red (FR) light regulate flowering through phytochromes, whereas blue light does so primarily through cryptochromes. In contrast, the role of green light in photoperiodic regulation of flowering has been inconsistent in previous studies. We grew four LDP species (two petunia cultivars, ageratum, snapdragon and Arabidopsis) and two SDP species (three chrysanthemum cultivars and marigold) in a greenhouse under truncated 9-h short days with or without 7-h day-extension lighting from green light (peak = 521 nm) at 0, 2, 13 or 25 μmol m-2 s-1 or R + white (W) + FR light at 2 μmol m-2 s-1 . Increasing the green photon flux density from 0 to 25 μmol m-2 s-1 accelerated flowering of all LDPs and delayed flowering of all SDPs. Petunia flowered similarly fast under R + W + FR light and moderate green light but was shorter and developed more branches under green light. To be as effective as R + W + FR light, saturation green photon flux densities were 2 μmol m-2 s-1 for LDP ageratum and SDP marigold and 13 μmol m-2 s-1 for LDP petunia. Snapdragon was the least sensitive to green light. In Arabidopsis, cryptochrome 2 mediated promotion of flowering under moderate green light, whereas both phytochrome B and cryptochrome 2 mediated that under R + W + FR light. We conclude that 7-h day-extension lighting from green light-emitting diodes can control flowering of photoperiodic ornamentals and that in Arabidopsis, cryptochrome 2 mediates promotion of flowering under green light.

CaVIL1, a plant homeodomain gene that promotes flowering in pepper.

CaVIL1 is a homolog of VIL1, a regulator of vernalization response in Arabidopsis and acts as a flowering promoter in pepper which does not respond to vernalization and photoperiod. As part of our goal to study the genetic and molecular basis of transition to flowering in pepper, we isolated the late-flowering mutant E-2698. Aside from late flowering, multiple pleiotropic alterations of the shoot structure, such as enlarged and distorted leaves, weak apical dominance, and reduced angle of the lateral branches were observed, indicating a broad role for the mutated gene in pepper development. Genetic mapping and sequence analyses revealed that the disrupted gene in E-2698 is the pepper homolog of VERNALIZATION INSENSITIVE 3-LIKE 1 (VIL1) that acts as a regulator of vernalization in Arabidopsis through chromatin modification. The pepper gene, CaVIL1, contains a plant homeodomain motif associated with chromatin modification and a VERNALIZATION INSENSITIVE 3-interacting domain that is truncated in E-2698 and in two other allelic mutants. Because pepper flowering does not respond to vernalization, we postulate that CaVIL1 regulates flowering time via chromatin modification of unknown targets. Expression analysis indicated that CaVIL1 activates the flowering promoter CaFLOWERING LOCUS T and represses the flowering repressor CaAPETALA2. Furthermore, CaVIL1 represses several genes from the FLOWERING LOCUS C (FLC)-LIKE clade that are clustered together in the pepper genome. This indicates their possible involvement in flowering regulation in this species. Our results show that CaVIL1 is a major regulator of flowering and interacts with other flowering promoters and repressors, as well as with FLC-LIKE genes whose function in flowering regulation is not yet known in pepper.

A SOC1-like gene MtSOC1a promotes flowering and primary stem elongation in Medicago.

Medicago flowering, like that of Arabidopsis, is promoted by vernalization and long days, but alternative mechanisms are predicted because Medicago lacks the key regulators CO and FLC. Three Medicago SOC1-like genes, including MtSOC1a, were previously implicated in flowering control, but no legume soc1 mutants with altered flowering were reported. Here, reverse transciption-quantitative PCR (RT-qPCR) indicated that the timing and magnitude of MtSOC1a expression was regulated by the flowering promoter FTa1, while in situ hybridization indicated that MtSOC1a expression increased in the shoot apical meristem during the floral transition. A Mtsoc1a mutant showed delayed flowering and short primary stems. Overexpression of MtSOC1a partially rescued the flowering of Mtsoc1a, but caused a dramatic increase in primary stem height, well before the transition to flowering. Internode cell length correlated with stem height, indicating that MtSOC1a promotes cell elongation in the primary stem. However, application of gibberellin (GA3) caused stem elongation in both the wild type and Mtsoc1a, indicating that the mutant was not defective in gibberellin responsiveness. These results indicate that MtSOC1a may function as a floral integrator gene and promotes primary stem elongation. Overall, this study suggests that apart from some conservation with the Arabidopsis flowering network, MtSOC1a has a novel role in regulating aspects of shoot architecture.

Effects of GA 3 on promotion of flowering in Kalanchoe spp.

Abstract Some species of Kalanchoe, including those of sections Kalanchoe and Bryophyllum do not flower naturally. This barrier to flowering might hinder hybridization and breeding. The role of gibberellin acid (GA3) in promoting flowering was investigated, and the effects of GA3 treatment on flowering under different temperatures were determined. The findings indicated that flowering was promoted in 100% of the K. sexangularis, K. nyikae, K. marnieriana, K. longiflora, and K. × richaudii plants treated with different GA3 gradients. The percentage of flowering in K. marnieriana and K. nyikae increased with increasing concentrations of applied GA3. The number of days taken to flower in K. nyikae and K. sexangularis decreased with increasing concentrations of applied GA3. In K. × richaudii treated with 100 mg L−1 GA3 flowers appeared the earliest. The number of flowers of K. sexangularis and K. × richaudii increased, while that of K. nyikae decreased, with increasing GA3 concentrations. GA3-treated K. nyikae, K. poincarei, and K. sexangularis plants showed higher percentages of flowering at 25/20 °C (day/night) than at higher temperatures. The findings from this study confirmed that GA3, applied in a broad range of concentrations, promotes floral induction in the studied species, affecting mainly the number of days taken to flower and the number of flowers produced. However, the GA3-treated plants had reduced flowering at higher temperatures. These findings can be applied in the regulation of flowering and breeding of Kalanchoe in future.

Promotion of Flowering from Far-red Radiation Depends on the Photosynthetic Daily Light Integral

Under natural short days, growers can use photoperiodic lighting to promote flowering of long-day plants and inhibit flowering of short-day plants. Unlike traditional lamps used for photoperiodic lighting, low-intensity light-emitting diode (LED) lamps allow for a wide array of adjustable spectral distributions relevant to regulation of flowering, including red (R) and white (W) radiation with or without far-red (FR) radiation. Our objective was to quantify how day-extension (DE) photoperiodic lighting from two commercially available low-intensity LED lamps emitting R + W or R + W + FR radiation interacted with daily light integral (DLI) to influence stem elongation and flowering of several ornamental species. Long-day plants [petunia (Petunia ×hybrida Vilm.-Andr. ‘Dreams Midnight’) and snapdragon (Antirrhinum majus L. ‘Oh Snap Pink’)], short-day plants [african marigold (Tagetes erecta L. ‘Moonsong Deep Orange’) and potted sunflower (Helianthus annuus L. ‘Pacino Gold’)], and day-neutral plants [pansy (Viola ×wittrockiana Gams. ‘Matrix Yellow’) and zinnia (Zinnia elegans Jacq. ‘Magellan Cherry’)] were grown at 20/18 °C day/night air temperatures and under low (6–9 mol·m−2·d−1) or high (16–19 mol·m−2·d−1) seasonal photosynthetic DLIs from ambient solar radiation combined with supplemental high-pressure sodium lighting and DE LED lighting. Photoperiods consisted of a truncated 9-hour day (0800–1700 hr) with additional 1-hour (1700–1800 hr, 10 hours total), 4-hour (1700–2100 hr, 13 hours total), or 7-hour (1700–2400 hr, 16 hours total) R + W or R + W + FR LED lighting at 2 μmol·m−2·s−1. Days to visible bud, plant height at first open flower, and time to first open flower (TTF) of each species were influenced by DLI, lamp type, and photoperiod though to different magnitudes. For example, plant height of african marigold and potted sunflower at first open flower was greatest under R + W + FR lamps, high DLIs, and 16-hour photoperiods. Petunia grown under R + W lamps, high DLI, and 10- and 13-hour photoperiods were the most compact. For all species, TTF was generally reduced under high DLIs. For example, regardless of the lamp type, flowering of african marigold occurred fastest under a high DLI and 10-hour photoperiod. Flowering of petunia and snapdragon occurred fastest under a high DLI, R + W + FR lamps, and a 16-hour photoperiod. However, only under high DLIs, R + W or R + W + FR lamps were equally effective at promoting flowering when used to provide DE lighting. Our data suggest that under low DLIs, flowering of long-day plants (petunia and snapdragon) occurs more rapidly under lamps providing R + W + FR, whereas under high DLIs, flowering is promoted similarly under either R + W or R + W + FR lamps.

PIL5 represses floral transition in Arabidopsis under long day conditions

PHYTOCHROME INTERACING FACTOR 3 LIKE 5 (PIL5), also named PHYTOCHROME INTERACTING FACTOR 1 (PIF1) is an important b-HLH transcription factor in Arabidopsis thaliana. Here we show that mutant of pil5-1 displays early flowering phenotype. We demonstrate that the expressions of the major flowering promoter genes [FLOWERING LOCUS T (FT), SUPPRESOR OF OVEREXPRESSION OF CO 1 (SOC1), and LEAFY (LFY)] are upregulated in the mutant of pil5-1. There is a significant increase of the mRNA of PIL5 in the mutants of co2-1, ft-10, soc1-2, and lfy-4. These changes provide the molecular evidence that PIL5 interacts with the flowering regulators to control flowering time. Moreover, it is shown in our results that PIL5 mutation mediates the increased contents of gibberellic acid (GA). Which is further supported by the qRT-PCR analysis, an increased transcriptome level of the GA biosynthesis genes (GA3ox1, GA3ox2, GA20ox1, GA20ox2, and GA20ox3) has been observed in the pil5-1 mutants as compared to the wild type. Collectively, PIL5 is involved in floral transition interacting with flowering integrators and GA.

Re-Evaluation of Florigen Transport Kinetics with Separation of Functions by Mutations That Uncouple Flowering Initiation and Long-Distance Transport.

In many plants, timing of flowering is regulated by day length. In Arabidopsis, florigen, FLOWERING LOCUS T (FT) protein, is synthesized in leaf phloem companion cells in response to long days and is transported to the shoot apical meristem (SAM) through the phloem. The temporal aspects of florigen transportation have been studied in various plants by physiological experiments. Nevertheless, little is known about how FT protein transportation is regulated in Arabidopsis. In this study, we performed heat shock-based transient FT induction in a single leaf blade and detected the FT protein in the shoot apex by 2D-PAGE. We demonstrated that detectable amounts of FT were transported from the leaf to the shoot apex within 8 h, and subsequent FT-induced target gene expression was detected within 8-12 h. Furthermore, we identified three amino acid residues (V70, S76 and R83) where missense mutations led to reduced mobility. Interestingly, these FT variants lost only their transportation ability, but retained their flowering promotion capacity, suggesting that discrete amino acids are involved in flowering regulation and transport regulation. Since the interaction with FT-INTERACTING PROTEIN 1 (FTIP1) was not affected in these FT variants, we hypothesize that the three amino acid residues are not involved in the FTIP1-mediated pathway of uploading, but rather in the subsequent step(s) of FT transport.

Direct interaction between VRN1 protein and the promoter region of the wheat FT gene.

The wheat florigen gene Wheat FLOWERING LOCUS T (WFT, which is identical to VRN3) is an integrator of the vernalization, photoperiod and autonomous pathways in wheat flowering. Many studies have indicated that VERNALIZATION 1 (VRN1) directly or indirectly up-regulates WFT expression in leaves. VRN1 encodes an APETALA1/FRUITFULL-like MADS box transcription factor that is up-regulated by vernalization and aging, leading to promotion of flowering. In this study, the VRN1 protein was expressed as a His-Tag fusion protein in Escherichia coli and used in an electrophoretic mobility shift assay (EMSA). The results from the EMSA indicated that the VRN1 protein directly binds to the CArG-box in the promoter region of WFT, suggesting the direct up-regulation of WFT by VRN1 in the leaves of wheat plants.

Effect of vernalization on tuberization and flowering in the Tibetan turnip is associated with changes in the expression of FLC homologues

The turnip (Brassica rapa var. rapa) is a biennial crop that is planted in late summer/early fall and forms fleshy tubers for food in temperate regions. The harvested tubers then overwinter and are planted again the next spring for flowering and seeds. FLOWERING LOCUS C (FLC) is a MADS-box transcription factor that acts as a major repressor of floral transition by suppressing the flowering promoters FT and SOC1. Here we show that vernalization effectively represses tuber formation and promotes flowering in Tibetan turnip. We functionally characterized four FLC homologues (BrrFLC1, FLC2, FLC3, and FLC5), and found that BrrFLC2 and BrrFLC1 play a major role in repressing flowering in turnip and in transgenic Arabidopsis. In contrast, tuber formation was correlated with BrrFLC1 expression in the hypocotyl and was repressed under cold treatment following the quantitative downregulation of BrrFLC1. Grafting experiments of non-vernalized and vernalized turnips revealed that vernalization independently suppressed tuberization in the tuber or hypocotyl of the rootstock or scion, which occurred in parallel with the reduction in BrrFLC1 activity. Together, our results demonstrate that the Tibetan turnip is highly responsive to cold exposure, which is associated with the expression levels of BrrFLC genes.