VASCULAR PLANT ONE-ZINC FINGER1 and VOZ2 repress the FLOWERING LOCUS C clade members to control flowering time in Arabidopsis

Floral transition is regulated by environmental and endogenous signals. Previously, we identified VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1) and VOZ2 as phytochrome B-interacting factors. VOZ1 and VOZ2 redundantly promote flowering and have pivotal roles in the downregulation of FLOWERING LOCUS C (FLC), a central repressor of flowering in Arabidopsis. Here, we showed that the late-flowering phenotypes of the voz1 voz2 mutant were suppressed by vernalization in the Columbia and FRIGIDA (FRI)-containing accessions, which indicates that the late-flowering phenotype of voz1 voz2 mutants was caused by upregulation of FLC. We also showed that the other FLC clade members, MADS AFFECTING FLOWERING (MAF) genes, were also a downstream target of VOZ1 and VOZ2 as their expression levels were also increased in the voz1 voz2 mutant. Our results suggest that the FLC clade genes integrate signals from VOZ1/VOZ2 and vernalization to regulate flowering.     

Floral transition mutants in Arabidopsis

An inventory of genetic differences in flowering time in Arabidopsis is presented and discussed. Many genes influence the transition to flowering in a quantitative way. Two groups of mutants and natural variants can be distinguished: those that are responsive to environmental factors and those that are less responsive or unresponsive. It is possible that all late/early-flowering mutants isolated to date carry a mutation with an effect, either promotive or repressive, on a floral repressor. The interaction between light perception and flowering has been studied by analysis of phytochrome- and cryptochrome-deficient mutants, which showed that phyA and probably also cryptochrome have a promotive role in flowering, whereas phyB and other stable phytochromes have an inhibitory role. A circadian rhythm is important in establishing daylength sensitivity, as was shown by the phenotype of the elf 3 mutants.     

Light-quality effects on Arabidopsis development. Red, blue and far-red regulation of flowering and morphology

Arabidopsis thaliana (L.) Heynh. race Columbia plants were grown in red. blue, red + far-red, blue + far-red and various light mixtures of red + blue + far-red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 μmol m⁻² s⁻¹) and the mixtures of red + blue + far-red maintained a constant ratio of red/far-red light, but varied in the ratio of blue to red + far-red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far-red absorbing form (P_fr/P_tot) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far-red and red + far-red light and late (55 days) in red light. In mixtures of red + blue + far-red light, each of which established a nearly constant P_fr/P_tot flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.     

The effect of daylength on the transition to flowering in phytochrome-deficient, late-flowering and double mutants of Arabidopsis thaliana

The effect of daylength on flowering was investigated in the following mutants of Arabidopsis thaliana : phytochrome B deficient ( hy3=phyB ); phytochrome chromophore deficient ( hy2 ); late-flowering ( co, gi. fca and fwa ); the hy2 and hy3 , late-flowering double mutants and the hy2, hy3 , late-flowering triple mutants. The hy mutants flower with fewer rosette leaves than the Landsberg erecta wild type under both long day and short day conditions and express this effect to a different degree in all late-flowering mutant backgrounds and under both daylengths, with the exception of fca under short days. The number of cauline leaves and days to flowering is less affected by the hy genotype. The hy2, hy3 double mutants flower with even fewer rosette leaves than the hy2 and hy3 monogenic mutants, suggesting an inhibitory role for phytochrome B and other stable phytochromes on flowering. The complex interaction between phytochrome, daylength and the effect of the late-flowering genes on the various parameters that describe the transition to flowering in Arabidopsis is discussed.     

Flowering responses to light-breaks in photomorphogenic mutants of Arabidopsis thaliana, a long-day plant

Flowering response and plant form of photomorphogenic mutants (hy1, hy2, hy3, hy4 and hy5) of Arabidopsis thaliana (L.), a long-day plant, were examined in long and short days. There were only slight differences among genotypes including Landsberg wild type with respect to the flowering time under long days. The effect of 1 h light-(night)-breaks of far-red, red, blue and white light given in the middle of the dark period of plants grown under short days, was studied. Effects of far-red light applied at the end or the beginning of the main photoperiod on flowering and plant form were also examined. The light-breaks with all the above mentioned light qualities promoted floral initiation of all the genotypes including the wild type in terms of both the flowering time and the number of rosette leaves. In general, far-red light was most effective. It is possible to classify the hy-mutants into 3 groups by their responses to light-breaks under short day conditions: (a) Mutants hy2 and hy3, which have a reduced number of rosette leaves, and flower early. Red light is as effective as far-red light. The wavelength of light-breaks is relatively unimportant for flowering response. (b) Mutants hy4, hy5 and Landsberg wild type, which have a greater number of rosette leaves, and flower relatively late. The effectiveness of light-breaks is in the following order, far-red, blue, and red light, which is in reverse order to the transformation of phytochrome to the P_fr form. (c) Mutant hy1, which behaves anomalously with respect to relations between flowering time and number of rosette leaves; late flowering with reduced number of rosette leaves. Red, blue and far-red light are effective, but white light is ineffective for reducing the number of rosette leaves. When far-red light was given in the middle of the night or at the end of the main photoperiod, it markedly reduced the number of rosette leaves compared to those grown under short days for all the genotypes, while when applied at the beginning of the main photoperiod far-red light did not affect the number of rosette leaves. Different effects on the plant form dependent on the time of treatment with far-red light-breaks are also discussed.     

Florigen （Ⅱ）： It is a Mobile Protein

The true identity of florigen - the molecule（s） that migrates from leaves to apical meristem to initiate flowering - was notoriously elusive, having made it almost the ＂Bigfoot＂ of plant biology. There was never a lack of drama in the field of florigen study, and florigen researchers have once again experienced such a swing in the last two years. We wrote a minireview last year in this journal （Yu et al. 2006） to excitedly salute, among other discoveries, the notion that the flowering locus T （FT） mRNA might be the molecular form of a florigen. However, this hypothesis was challenged in a little less than two years after its initial proposition, and the original paper proposed that the FT mRNA hypothesis was retracted （Huang et al. 2005; Bohlenius et al. 2007）. Interestingly enough, the FT gene previously proposed to encode a florigen was never challenged. Rather, the FT protein, instead of the FT mRNA, is now believed to migrate from leaves to the apical meristem to promote floral initiation. In this update, we will share with our readers some entertaining stories concerning the recent studies of florigen in five different plant species. In addition to the published reports referenced inthis update, readers may also refer to our previous minireview and references therein for additional background information （Yu et al. 2006）.     

光受体介导信号转导调控植物开花研究进展

光照是影响植物生长发育的重要环境因子, 开花是高等植物生活史上最重要的事件。植物通过光受体感知外界环境中的光照变化, 激活一系列信号转导过程从而适时开花。该文介绍了高等植物光受体的种类、结构特征和生理功能的研究进展, 并系统阐述了红光/远红光受体光敏色素、蓝光受体隐花色素以及FKF1/ZTL/LKP2等介导光信号调控植物开花的分子机制, 包括光受体对CO转录及转录后水平调控和对FT转录水平的调控等。此外, 还介绍了光受体整合光信号与温度和赤霉素等信号调控植物开花的研究进展, 并展望了未来的研究方向。     

A new role for phytochromes in temperature-dependent germination

Germination timing is a fundamental life-history trait, as seedling establishment predicates realized fitness in the wild. Light and temperature are two important cues by which seeds sense the proper season of germination. Using Arabidopsis thaliana, we provide evidence that phytochrome-mediated germination pathways simultaneously respond to light and temperature cues in ways that affect germination. Phytochrome mutant seeds were sown on agar plates and allowed to germinate in lit, growth chambers across a range of temperatures (7 degrees C to 28 degrees C). phyA had an important role in promoting germination at warmer temperatures, phyE was important to germination at colder temperatures and phyB was important to germination across a range of temperatures. Different phytochromes were required for germination at different temperatures, indicating a restriction or even a potential specialization of individual phytochrome activity as a function of temperature. This temperature-dependent activity of particular phytochromes reveals a potentially novel role for phytochrome pathways in regulating the seasonal timing of germination.     

Dual effect of phytochrome A on hypocotyl growth under continuous red light

The role of phytochrome A in the control of hypocotyl growth under continuous red light (Rc) was investigated using phyA and phyB mutants of Arabidopsis thaliana, which lack phytochrome A (phyA) or phytochrome B (phyB), respectively, and transgenic seedlings of Nicotiana tabacum overexpressing Avena phyA, compared to the corresponding wild type (WT). In WT seedlings of A. thaliana, hypocotyl growth inhibition showed a biphasic response to the fluence rate of Rc, with a brake at 10^?2μmol m^?2 s^?1. At equal total fluence rate, hourly pulses of red light caused slightly more inhibition than Rc. The response to very low fluences of continuous or pulsed red light was absent in the phyA and phyA phyB mutants and present in the phyB mutant. The second part of the response was steeper in the phyA mutant than in the WT but was absent in the phyB mutant. In WT tobacco the response to Rc was biphasic. Overexpression of Avena phyA enhanced the response only at very low fluence rates of Rc (< 10^?2μmol m^?2 s^?1). In both species, the effect of hourly pulses of far-red light was similar to the maximum inhibition observed in the first phase of the response to Rc. Using reciprocity failure (i.e. higher inhibition under continuous than pulsed light) as the operational criterion, a ‘true’ high-irradiance reaction occurred under continuous far-red light but not under Rc or red plus far-red light mixtures. Native and overexpressed phyA are proposed to mediate very low fluence responses under Rc. In WT A. thaliana, this effect is counteracted by a negative action of phyA on phyB-mediated low-fluence responses.     

Absence of phyB inhibits hypocotyl elongation in dark-grown Ih cucumber seedlings: an active role for PrB

Cucumber (Cucumis sativus L.) seedlings carrying the long hypocotyl (Ih) mutation, which confers a lack of B-type phytochrome (phyB), were significantly shorter than their near-isogenic wild-type counterparts when grown in complete darkness. Relative growth rates determined for 5 mm hypocotyl regions were lower in Ih seedlings in all growing regions, and the zone of elongation was less extensive in Ih hypocotyls. Digital imaging microscopy revealed that the pattern of epidermal cell lengths along the stem axis differed between the Ih mutant and the iso-genic wild-type. These findings (and the fact that experiments were conducted under conditions where phytochrome photoconversion to the far-red-absorbing form does not occur) suggest that the red-absorbing form of phyB (PrB) is an active positive regulator of development in etiolated plants.     

植物成花转变及成花逆转的研究进展

本文主要讨论了植物成花转变及成花逆转等开花研究中应用分子生物学技术所取得的一些进展,描述了成花决定态的特性,5个从拟南芥中分离获得的成花转变的基因,有关光受体的分子生物学研究和造成成花逆转的原因等。     

Flowering of Pharbitis nil is controlled by an endogenous semidian rhythm

Abstract Flowering of Pharbitis nil after an inductive dark period is greatly influenced by far-red (FR) irradiation during the preceding light period. The response to FR is rhythmic in otherwise constant conditions, and the period of the oscillation is approximately 12 h (i.e. semidian). The rhythm also appears to operate under daily light-dark cycles. The expression of this novel rhythm depends on the time from the beginning of FR pretreatment to the onset of the inductive dark period. The cotyledons are the site of response to both the pretreatment and inductive darkness, and both these conditions must be perceived by the same cotyledon.