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At least 19 recordsLinked to original sources
PubMed1994

Phytochrome B and at Least One Other Phytochrome Mediate the Accelerated Flowering Response of Arabidopsis thaliana L. to Low Red/Far-Red Ratio.

We have investigated the involvement of phytochrome B in the early-flowering response of Arabidopsis thaliana L. seedlings to low red:far-red (R/FR) ratio light conditions. The phytochrome B-deficient hy3 (phyB) mutant is early flowering, and in this regard it resembles the shade-avoidance phenotype of its isogenic wild type. Seedlings carrying the hy2 mutation, resulting in a deficiency of phytochrome chromophore and hence of active phytochromes, also flower earlier than wild-type plants. Whereas hy3 or hy2 seedlings show only a slight acceleration of flowering in response to low R/FR ratio, seedlings that are doubly homozygous for both mutations flower earlier than seedlings carrying either phytochrome-related mutation alone. This additive effect clearly indicates the involvement of one or more phytochrome species in addition to phytochrome B in the flowering response as well as indicating the presence of some functional phytochrome B in hy2 seedlings. Seedlings that are homozygous for the hy3 mutation and one of the fca, fwa, or co late-flowering mutations display a pronounced early-flowering response to low R/FR ratio. A similar response to low R/FR ratio is displayed by seedlings doubly homozygous for the hy2 mutation and any one of the late-flowering mutations. Thus, placing the hy3 or hy2 mutations into a late-flowering background has the effect of uncovering a flowering response to low R/FR ratio. Seedlings that are triply homozygous for the hy3, hy2 mutations and a late-flowering mutation flower earlier than the double mutants and do not respond to low R/FR ratio. Thus, the observed flowering responses to low R/FR ratio in phytochrome B-deficient mutants can be attributed to the action of at least one other phytochrome species.

Journal Article↗
PubMed2004

Ectopic expression of the petunia MADS box gene UNSHAVEN accelerates flowering and confers leaf-like characteristics to floral organs in a dominant-negative manner.

Several genes belonging to the MADS box transcription factor family have been shown to be involved in the transition from vegetative to reproductive growth. The Petunia hybrida MADS box gene UNSHAVEN (UNS) shares sequence similarity with the Arabidopsis thaliana flowering gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1, is expressed in vegetative tissues, and is downregulated upon floral initiation and the formation of floral meristems. To understand the role of UNS in the flowering process, knockout mutants were identified and UNS was expressed ectopically in petunia and Arabidopsis. No phenotype was observed in petunia plants in which UNS was disrupted by transposon insertion, indicating that its function is redundant. Constitutive expression of UNS leads to an acceleration of flowering and to the unshaven floral phenotype, which is characterized by ectopic trichome formation on floral organs and conversion of petals into organs with leaf-like features. The same floral phenotype, accompanied by a delay in flowering, was obtained when a truncated version of UNS, lacking the MADS box domain, was introduced. We demonstrated that the truncated protein is not translocated to the nucleus. Using the overexpression approach with both the full-length and the nonfunctional truncated UNS protein, we could distinguish between phenotypic alterations because of a dominant-negative action of the protein and because of its native function in promoting floral transition.

Arabidopsis↗
PubMed2004

Acceleration of flowering by overexpression of MFT (MOTHER OF FT AND TFL1).

MFT (MOTHER OF FT AND TFL1) is a member of a gene family that includes two important regulators, FT (FLOWERING LOCUS T) and TFL1 (TERMINAL FLOWER 1), in determination of flowering time in Arabidopsis. Although the functions of FT and TFL1 are assigned in the family, the roles of other members are largely unknown. Especially the sequence of MFT is homologous to both FT and TFL1, which act as a floral promoter and an inhibitor, respectively, making it difficult to predict the role of MFT. We performed genetic analyses of MFT to understand its role in floral development. Constitutive expression of MFT led to slightly early flowering under long days. However, a T-DNA insertion allele of MFT did not show obvious phenotype. Further genetic analyses with the loss-of-function alleles of FT, TFL1, and ATC (Arabidopsis Thaliana CENTRORADIALIS homologue) showed that a decrease of MFT activity did not enhance the phenotypes of the single mutants. Taken together, we suggest that MFT functions as a floral inducer and that it may act redundantly in determination of flowering time in Arabidopsis.

Alleles↗
PubMed2006

Regulation of flowering time by Arabidopsis MSI1.

The transition to flowering is tightly controlled by endogenous programs and environmental signals. We found that MSI1 is a novel flowering-time gene in Arabidopsis. Both partially complemented msi1 mutants and MSI1 antisense plants were late flowering, whereas ectopic expression of MSI1 accelerated flowering. Physiological experiments revealed that MSI1 is similar to genes from the autonomous promotion of flowering pathway. Expression of most known flowering-time genes did not depend on MSI1, but the induction of SOC1 was delayed in partially complemented msi1 mutants. Delayed activation of SOC1 is often caused by increased expression of the floral repressor FLC. However, MSI1 function is independent of FLC. MSI1 is needed to establish epigenetic H3K4 di-methylation and H3K9 acetylation marks in SOC1 chromatin. The presence of these modifications correlates with the high levels of SOC1 expression that induce flowering in Arabidopsis. Together, the control of flowering time depends on epigenetic mechanisms for the correct expression of not only the floral repressor FLC, but also the floral activator SOC1.

Arabidopsis↗
PubMed2001

Three MADS-box genes similar to APETALA1 and FRUITFULL from silver birch (Betula pendula).

Despite intensive research on genetic regulation of flower development there are still only a few studies on the early phases of this process in perennial plants like trees. The aim of this study has been to identify genes that regulate early stages of inflorescence development in silver birch (Betula pendula Roth) and to follow the expression of these genes during development of the unisexual birch inflorescences. Here we describe the cloning and characterization of 3 cDNAs representing MADS-box genes designated BpMADS3, BpMADS4 and BpMADS5, all belonging to the AP1/SQUA group of plant MADS-box genes. According to RNA blot analysis, all 3 genes are active during the development of both male and female inflorescences. However, differences in patterns of expression suggest that they play different roles. BpMADS3 is most similar in sequence to AP1 and SQUA, but it seems to have the highest expression at late developmental stages. BpMADS4 is most similar in sequence to the Arabidopsis gene FRUITFULL, but is expressed, in addition to developing inflorescences, in shoots and roots. BpMADS5 is also similar to FRUITFULL; its expression seems to be inflorescence-specific and continues during fruit development. Ectopic expression of either BpMADS3, BpMADS4 or BpMADS5 with the CaMV 35S promoter in tobacco results in extremely early flowering. All of these birch genes seem to act early during the transition to reproductive phase and might be involved in the determination of the identity of the inflorescence or flower meristem. They could apparently be used to accelerate flowering in various plant species.

Journal Article↗
PubMed1998

Studies on flower initiation of Super-Dwarf wheat under stress conditions simulating those on the Space Station, Mir.

Super-Dwarf wheat plants were grown in growth chambers under 12 treatments with three photoperiods (18 h, 21 h, 24 h) and four carbon dioxide (CO2) levels (360, 1,200, 3,000 and 7,000 micromoles mol-1). Carbon dioxide concentrations affected flower initiation rates of Super-Dwarf wheat. The optimum CO2 level for flower initiation and development was 1,200 micromoles mol-1. Super-optimum CO2 levels delayed flower initiation, but did not decrease final flower bud number per head. Longer photoperiods not only accelerated flower initiation rates, but also decreased deleterious effects of super-optimum CO2. Flower bud size and head length at the same developmental stage were larger under longer photoperiods, but final flower bud number was not affected by photoperiod.

Carbon Dioxide↗
PubMed2000

LEAFY and the evolution of rosette flowering in violet cress (Jonopsidium acaule, Brassicaceae).

Arabidopsis and most other Brassicaceae produce an elongated inflorescence of mainly ebracteate flowers. However, the early-flowering species violet cress (Jonopsidium acaule) and a handful of other species produce flowers singly in the axils of rosette leaves. In Arabidopsis the gene LEAFY (LFY) is implicated in both the determination of flower meristem identity and in the suppression of leaves (bracts) that would otherwise subtend the flowers. In this study we examined the role of LFY homologs in the evolution of rosette flowering in violet cress. We cloned two LFY homologs, vcLFY1 and vcLFY2, from violet cress. Their exon sequences show ∼90% nucleotide similarity with Arabidopsis LFY and 99% similarity to each other. We used in situ hybridization to study vcLFY expression in violet cress. The patterns were very similar to LFY in Arabidopsis except for stronger expression in the shoot apical meristem outside of the region of flower meristem initiation. It is possible that the relatively diffuse expression of vcLFY contributes to the lack of bract suppression in violet cress. Additionally, the earliest flowers produced by violet cress express vcLFY, suggesting that accelerated flowering in violet cress could also result from changes in the regulation of vcLFY.

Journal Article↗
PubMed2005

[Functional analysis of vernalization-related gene VER17 in flower development using antisense RNA strategy in winter wheat].

To understand the function of vernalization-related gene VER17 in winter wheat (Triticum aestivum L. cv. Jingdong No.1), an antisense RNA strategy was used. The antisense VER17 with a vector pBI121 was constructed and transformed into winter wheat by using the pollen-tube-pathway method. Fourteen independent transgenic plants transformed with antisense VER17 and five control transformants transformed with pBI121 blank vector were obtained and confirmed by GUS histochemical assay and PCR-Southern blot analysis. Phenotypes of T(0) and T(1) transgenic plants showed that the plants of the antisense VER17 transgenic lines degenerated top or basal spikelets and had delayed flowering time, which suggested that the VER17 gene functions in accelerating flowering and the development of the top or basal spikelets and the stamen which were impacted by vernalization treatment.

Blotting, Southern↗
PubMed2002

Control of photoperiod-regulated tuberization in potato by the Arabidopsis flowering-time gene CONSTANS.

Photoperiod controls several responses throughout the plant life cycle, like germination, flowering, tuber formation, onset of bud dormancy, leaf abscission, and cambium activity. From these processes, flowering has been most extensively studied, especially in Arabidopsis thaliana. Photoperiod sensing by the function of photoreceptors and the circadian clock appears to regulate flowering time via Arabidopsis CONSTANS (AtCO), a putative transcription factor that accelerates flowering in response to long days. The genetic factors controlling plant photoperiodic responses other than flowering are little known. However, interspecific grafting experiments demonstrated that the flower-inducing (florigen) and tuber- inducing (tuberigen) signals are functionally exchangeable. Here we show that constitutive overexpression in potato of the Arabidopsis flowering-time gene AtCO impairs tuberization under short-day inductive conditions; AtCO overexpressing lines require prolonged exposure to short days to form tubers. Grafting experiments using these lines indicated that AtCO exerts its inhibitory effect on tuber formation by acting in the leaves. We propose that a conserved photoperiodic functional module may be involved in controlling distinct photoperiod-regulated evocation responses in different species. This module would involve the action of CONSTANS in the production of the elusive and long-distance acting florigen-tuberigen signal(s) in the leaves.

Arabidopsis↗
PubMed2004

Functional characterization of SEPALLATA3 and AGAMOUS orthologues in silver birch.

The development of flowers is regulated by a complex network of transcriptional activators and repressors, many of which belong to the MADS box gene family. In this study, we describe two MADS box genes of silver birch (Betula pendula Roth), BpMADS1 and BpMADS6, which are similar to SEPALLATA3 and AGAMOUS in Arabidopsis thaliana, respectively. In situ hybridization showed that BpMADS1 was expressed in the inflorescence meristem at a very early stage, but not later. Both genes were expressed in developing carpels, ovules and stamens but not in tepals or scales. Ectopic expression of BpMADS1 in Arabidopsis resulted in a reduced number of floral organs or whole whorls and in petaloid or carpelloid sepals, a phenotype reminiscent of that of fil mutants. 35S::BpMADS6 caused very early flowering in Arabidopsis. In tobacco, both 35S::BpMADS1 and 35S::BpMADS6 accelerated flowering and, in addition, 35S::BpMADS6 caused changes in sepals and petals. In some transgenic birch plants, 35S::BpMADS1 antisense resulted in the development of both male and female organs in the axil of a single bract and in a change of some inflorescences into vegetative shoots. In two plants, either 35S::BpMADS6 sense or antisense constructs resulted in an increase in the number of tepals and in complete lack of stamens in some male inflorescences. These results suggest that BpMADS1 participates both in inflorescence and in flower formation and BpMADS6 participates in flower formation and that they are functional homologues to SEPALLATA3 and AGAMOUS, respectively.

Journal Article↗
PubMed2000

Integration of floral inductive signals in Arabidopsis.

Flowering of Arabidopsis is regulated by a daylength-dependent pathway that accelerates flowering in long days and a daylength-independent pathway that ensures flowering in the absence of inductive conditions. These pathways are genetically separable, as there are mutations that delay flowering in long but not short days. Conversely, mutations that block synthesis of the hormone gibberellin abolish flowering in short days, but have on their own only a minor effect in long days. A third pathway, the autonomous pathway, probably acts by modulating the other two pathways. Understanding where and how these pathways are integrated is a prerequisite for understanding why similar environmental or endogenous cues can elicit opposite flowering responses in different plants. In Arabidopsis, floral induction leads ultimately to the upregulation of floral meristem-identity genes such as LEAFY, indicating that floral inductive signals are integrated upstream of LEAFY Here we show that gibberellins activate the LEAFY promoter through cis elements that are different from those that are sufficient for the daylength response, demonstrating that the LEAFY promoter integrates environmental and endogenous signals controlling flowering time.

Arabidopsis↗
PubMed2005

Analysis of flowering pathway integrators in Arabidopsis.

Flowering is regulated by an integrated network of several genetic pathways in Arabidopsis. The key genes integrating multiple flowering pathways are FT, SOC1 and LFY. To elucidate the interactions among these integrators, genetic analyses were performed. FT and SOC1 share the common upstream regulators CO, a key component in the long day pathway, and FLC, a flowering repressor integrating autonomous and vernalization pathways. However, the soc1 mutation further delayed the flowering time of long day pathway mutants including ft, demonstrating that SOC1 acts partially independently of FT. Although soc1 did not show an obvious defect in flower meristem determination on its own, it dramatically increased the number of coflorescences in a lfy mutant, which is indicative of a defect in floral initiation. Therefore, double mutant analysis shows that the three integrators have both overlapping and independent functions in the determination of flowering time and floral initiation. The expression analysis showed that FT regulates SOC1 expression, and SOC1 regulates LFY expression, but not vice versa, which is consistent with the fact that FT and LFY have the least overlapping functions among the three integrators. The triple mutation ft soc1 lfy did not block flowering completely under long days, indicating the presence of other integrators. Finally, vernalization accelerated flowering of flc ft soc1 and ft soc1 lfy triple mutants, which shows that the vernalization pathway also has targets other than FLC, FT, SOC1 and LFY. Our genetic analysis reveals the intricate nature of genetic networks for flowering.

Arabidopsis↗
PubMed2001

CONSTANS mediates between the circadian clock and the control of flowering in Arabidopsis.

Flowering is often triggered by exposing plants to appropriate day lengths. This response requires an endogenous timer called the circadian clock to measure the duration of the day or night. This timer also controls daily rhythms in gene expression and behavioural patterns such as leaf movements. Several Arabidopsis mutations affect both circadian processes and flowering time; but how the effect of these mutations on the circadian clock is related to their influence on flowering remains unknown. Here we show that expression of CONSTANS (CO), a gene that accelerates flowering in response to long days, is modulated by the circadian clock and day length. Expression of a CO target gene, called FLOWERING LOCUS T (FT), is restricted to a similar time of day as expression of CO. Three mutations that affect circadian rhythms and flowering time alter CO and FT expression in ways that are consistent with their effects on flowering. In addition, the late flowering phenotype of such mutants is corrected by overexpressing CO. Thus, CO acts between the circadian clock and the control of flowering, suggesting mechanisms by which day length regulates flowering time.

Arabidopsis↗
PubMed2003

Isolation and characterization of phyC mutants in Arabidopsis reveals complex crosstalk between phytochrome signaling pathways.

Studies with mutants in four members of the five-membered Arabidopsis phytochrome (phy) family (phyA, phyB, phyD, and phyE) have revealed differential photosensory and/or physiological functions among them, but identification of a phyC mutant has proven elusive. We now report the isolation of multiple phyC mutant alleles using reverse-genetics strategies. Molecular analysis shows that these mutants have undetectable levels of phyC protein, suggesting that they are null for the photoreceptor. phyC mutant seedlings were indistinguishable from wild-type seedlings under constant far-red light (FRc), and phyC deficiency had no effect in the phyA mutant background under FRc, suggesting that phyC does not participate in the control of seedling deetiolation under FRc. However, when grown under constant red light (Rc), phyC seedlings exhibited a partial loss of sensitivity, observable as longer hypocotyls and smaller cotyledons than those seen in the wild type. Although less severe, this phenotype resembles the effect of phyB mutations on photoresponsiveness, indicating that both photoreceptors function in regulating seedling deetiolation in response to Rc. On the other hand, phyB phyC double mutants did not show any apparent decrease in sensitivity to Rc compared with phyB seedlings, indicating that the phyC mutation in the phyB-deficient background does not have an additive effect. These results suggest that phyB is necessary for phyC function. This functional dependence correlates with constitutively lower levels of phyC observed in the phyB mutant compared with the wild type, a decrease that seems to be regulated post-transcriptionally. phyC mutants flowered early when grown in short-day photoperiods, indicating that phyC plays a role in the perception of daylength. phyB phyC double mutant plants flowered similarly to phyB plants, indicating that in the phyB background, phyC deficiency does not further accelerate flowering. Under long-day photoperiods, phyA phyC double mutant plants flowered later than phyA plants, suggesting that phyC is able to promote flowering in the absence of phyA. Together, these results suggest that phyC is involved in photomorphogenesis throughout the life cycle of the plant, with a photosensory specificity similar to that of phyB/D/E and with a complex pattern of differential crosstalk with phyA and phyB in the photoregulation of multiple developmental processes.

Arabidopsis↗
PubMed2002

Multiple roles of Arabidopsis VRN1 in vernalization and flowering time control.

Arabidopsis VRN genes mediate vernalization, the process by which a long period of cold induces a mitotically stable state that leads to accelerated flowering during later development. VRN1 encodes a protein that binds DNA in vitro in a non-sequence-specific manner and functions in stable repression of the major target of the vernalization pathway, the floral repressor FLC. Overexpression of VRN1 reveals a vernalization-independent function for VRN1, mediated predominantly through the floral pathway integrator FT, and demonstrates that VRN1 requires vernalization-specific factors to target FLC.

Amino Acid Sequence↗
PubMed2006

SUPPRESSOR OF FRIGIDA4, encoding a C2H2-Type zinc finger protein, represses flowering by transcriptional activation of Arabidopsis FLOWERING LOCUS C.

FLOWERING LOCUS C (FLC), a strong floral repressor, is one of the central regulators of flowering in Arabidopsis thaliana. The expression of FLC is increased by FRIGIDA (FRI) but decreased by vernalization, a long period of cold exposure that accelerates flowering. Although many aspects of FLC regulation have been reported, it is not known how FLC is transcriptionally activated by FRI at the molecular level. We isolated suppressor of FRIGIDA4 (suf4), a mutant that flowers early as a result of low FLC expression. SUF4 encodes a nuclear-localized protein with two C2H2-type zinc finger motifs and a Pro-rich domain. SUF4 protein interacts with FRI and FRIGIDA-LIKE1 (FRL1), two genes for which single mutations have the same phenotype as suf4. SUF4 also bound to the promoter of FLC in a chromatin immunoprecipitation assay, suggesting that SUF4 acts as a transcriptional activator of FLC after forming a complex with FRI and FRL1. In addition, suf4 suppresses luminidependens (ld), a late-flowering mutation that causes an increase of FLC, and SUF4 protein directly interacts with LD. Thus, we propose that LD binds to SUF4 to suppress its activity in the absence of FRI.

Arabidopsis↗
PubMed1992

Gibberellin Is Required for Flowering in Arabidopsis thaliana under Short Days.

Mutants of Arabidopsis thaliana deficient in gibberellin synthesis (ga1-3 and ga1-6), and a gibberellin-insensitive mutant (gai) were compared to the wild-type (WT) Landsberg erecta line for flowering time and leaf number when grown in either short days (SD) or continuous light (CL). The ga1-3 mutant, which is severely defective in ent-kaurene synthesis because it lacks most of the GA1 gene, never flowered in SD unless treated with exogenous gibberellin. After a prolonged period of vegetative growth, this mutant eventually underwent senescence without having produced flower buds. The gai mutant and the "leaky" ga1-6 mutant did flower in SD, but took somewhat longer than WT. All the mutants flowered readily in CL, although the ga1-3 mutant showed some delay. Unlike WT and ga1-3, the gai mutant failed to respond to gibberellin treatment by accelerating flowering in SD. A cold treatment promoted flowering in the WT and gai, but failed to induce flowering in ga1-3. From these results, it appears that gibberellin normally plays a role in initiating flowering of Arabidopsis.

Journal Article↗