Regulation of Flowering Time by MicroRNAs

The shoot apical meristem (SAM) continuously produces lateral organs in plants.Based on the identity of the lateral organs,the life cycle of a plant can be divided into two phases:vegetative and reproductive.The SAM produces leaves during the vegetative phase,whereas it gives rise to flowers in the reproductive phase (reviewed in Poethig,2003).The floral transition,namely the switch from vegetative to reproductive growth,is controlled by diverse endogenous and exogenous cues such as age,hormones,photoperiod,and temperature (reviewed in B(a)urle and Dean,2006;Srikanth and Schmid,2011;Andres and Coupland,2012). The model annual Arabidopsis thaliana has been extensively used for the dissection of the molecular mechanism underlying the floral transition during the last two decades.The molecular and genetic analyses have revealed five flowering time pathways,including age,autonomous,gibberellins (GAs),photoperiod and vernalization (reviewed in Amasino and Michaels,2010).Growing lines of evidence indicate that there are extensive crosstalks,feedback or feed-forward loops between the components within these pathways,and that these multiple floral inductive cues are integrated into a set of floral promoting MADS-box genes including APETALA 1 (AP1),SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1),FRUITFULL (FUL) and LEAFY (LFY) (Amasino and Michaels,2010;Lee and Lee,2010;Srikanth and Schmid,2011).     

同源异型基因对花器官发育的调控

以ABC模型为基础,阐述了花器官发育调控的分子机制,对一些相关基因在其中的作用和研究进展作了介绍.     

MADS-box基因控制植物成花的分子机理

植物花器官的发育和开花是植物生殖发育中最重要的过程,植物在长期的进化过程中产生了春化(低温)途径、自主途径、光周期途径以及不依赖于光温环境条件的赤霉素信号途径来适应多变的环境和调控植物开花过程。本文综述了模式植物拟南芥中由LEAFY(LFY)、CONSTANS(CO)、FLOWERING LOCUSC(FLC)、FLOW ERING LOCUS T(FT)和SUPPRESSOR OF OVEREXPRESSION OF CO1(SOC1)等基因构成的双子叶植物响应光温条件变化的开花调控网络;以及大麦、小麦中由VERNALIZATION1(VRN1)、VRN2、ODD-SOC2(OS2)和拟南芥CO、FT同源基因构成的禾本科植物开花调控网络。其中最重要的是转录调控因子MADS-box基因FLC、SOC1、VRN1和OS2,并发现组蛋白的乙酰化/脱乙酰化,赖氨酸的甲基化/脱甲基化在调控FLC、VRN1染色质活性状态及基因表达,从而产生开花控制的机理。这些研究发现将有助于对具有重要经济价值的单双子叶植物,通过生物技术手段改良其品种特性以应对非生物逆境,特别是低温胁迫的指导。     

拟南芥开花时间调控的分子基础

在合适的时间开花对大多数植物的生存和成功繁衍极为重要。开花时间受错综复杂的环境因素和植物自身的遗传因子影响,由开花调控因子所构成的光周期、春化、温度、赤霉素、自主以及年龄等至少6条既相互独立又相互联系的遗传途径调控。该文综述了有关拟南芥(Arabidopsis thaliana)开花时间调控的分子机制的最新研究进展,并对今后的研究进行了展望。     

Nitrogen Mediates Flowering Time and Nitrogen Use Efficiency via Floral Regulators in Rice

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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。     

拟南芥开花过程的表观遗传调节

开花是高等植物由营养生长到生殖生长的重要转变.拟南芥的开花时间受许多基因的调控,其中一些基因的表现遗传调节对开花时间的控制发挥着重要的作用.本文就这些基因以表观遗传方式调节拟南芥开花过程的最新研究进程作简要介绍.     

高等植物开花时程的调控与光受体Ⅰ.开花时程的基因与光受体调控

系统评述了高等植物开花时程的调控与植物光受体的联系.重点说明了控制开花时程的遗传途径以及光周期途径的有关基因的研究进展.影响高等植物开花的最重要的因子之一便是光周期,光周期对高等植物开花的调控是通过相关基因间的相互作用来实现的,这些基因包括参与花启动发育控制基因,昼夜节律时间钟调控基因及光受体信号转导基因.近5年左右的时间通过对拟南芥及其一系列突变体的研究为我们展示了这一热门领域的广阔的前景.     

The Role of VIN3-LIKE Genes in Environmentally Induced Epigenetic Regulation of Flowering

Given their sessile nature, it is critical for the survival of plants to adapt to their environment. Accordingly, plants have evolved the ability to sense seasonal changes to govern developmental fates such as the floral transition. Temperature and day length are among the seasonal cues that plants sense. We recently reported that VIN3-LIKE 1 (VIL1) is involved in mediating the flowering response to both cold and day length via regulation of two related genes, FLOWERING LOCUS C (FLC) and FLOWERING LOCUS M (FLM), respectively.Key Words: flowering, vernalization, photoperiod, chromatin, histone, gene expressionVernalization renders plants competent to flower after exposure to the prolonged cold of winter.^1,2 Arabidopsis exhibits facultative responses to both vernalization and photoperiod to initiate the floral transition. The facultative nature of the responses makes Arabidopsis a tractable genetic system to study these aspects of flowering time control.In Arabidopsis, vernalization creates competence to flower via silencing of the potent floral repressor, FLC, in a mitotically stable manner.^3,4 Thus, the vernalization response is an environmentally induced epigenetic switch in that exposure to cold permanently affects the plants'' developmental program. This epigenetic switch is associated with increased levels of FLC chromatin methylation on Histone H3 Lys 9 and Lys 27.^5,6 VERNALIZATION INSENSITIVE 3 (VIN3) plays an essential role in this switch since no modifications to FLC chromatin occur in vin3 mutants.⁵ Furthermore, the levels of expression of VIN3 mRNA are tightly correlated with the degree of the vernalization response.⁵ VIN3 encodes Plant HomeoDomain (PHD) finger-containing protein. PHD finger-containing proteins are often associated with protein complexes that are involved in chromatin remodeling.⁷We performed a yeast two-hybrid screen to identify potential protein partners of VIN3. VIN3-LIKE 1 (VIL1) was identified by this screen.⁸ VIL1 encodes a PHD finger-containing protein that is related to VIN3. As expected for proteins that are associated with VIN3, plants containing loss-of-function alleles of VIL1 do not respond to vernalization. Furthermore, no vernalization-mediated histone modifications occur at FLC in vil1 mutants similar to the situation in vin3 mutants. Thus, by yeast two hybrid and genetic analysis, VIL1 is a bona fide VIN3 partner that is required for vernalization-mediated histone modifications at FLC chromatin. Unlike VIN3, the expression of VIL1 does not change over the course of cold exposure. Rather, VIL1 mRNA levels are affected by photoperiod. VIL1 expression is significantly increased in non-inductive photoperiods (short days; SD). Consistent with this expression pattern, vil1 mutants in the Columbia accession exhibit a SD-specific late-flowering phenotype. Furthermore, VIL1 is required for attenuating expression of FLOWERING LOCUS M, a FLC-related gene, in a SD-specific manner. It is possible that the attenuation of FLM by VIL1 has a role in creating the facultative nature of photoperiod response in Arabidopsis since vil1 mutants tend towards an obligate photoperiod response (i.e., vil1 mutants often fail to flower in SD).In Arabidopsis, there are four VIN3-related genes, which we named as VIL1 ∼ VIL4,⁸ and which have also been called VRN5 and VEL1 ∼ VEL3.⁹ The C-terminal domain is highly conserved among these genes and was named the VIN3-Interacting Domain (VID) since it is required for protein-protein interaction between VIN3 and VIL1. The effect of cold on the expression patterns of VIN3-related genes varies. For example, VIL2 and VIL3 are induced specifically by vernalizing cold exposures whereas others such as VIL1 are, for the most part, constitutively expressed. It will be interesting to determine the functions of the remaining VIL genes.FLC is the main target for vernalization in Arabidopsis. Interestingly, FLC orthologs have not been found in vernalization-responsive varieties of cereals. However, in wheat, VRN2 appears to have a role equivalent to that of FLC in Arabidopsis.¹⁰ VRN2 encodes a ZCCT type zinc-finger protein that does not have a homolog in the Arabidopsis genome. In diploid wheat, down regulation of VRN2 is correlated with the vernalization response.¹¹ Interestingly, wheat contains three VIN3-LIKE (VIL) genes, TmVIL1, TmVIL2 and TmVIL3.¹² Furthermore, TmVIL1 is up-regulated by vernalization.¹² However, whether TmVIL1 has a direct role in the vernalization-mediated repression of VRN2 in wheat has not yet been addressed. Similar to VIL1, TmVIL3 shows elevated level of expression in SD. Furthermore, VRN2 is downregulated in SD;^13,14 thus there is a correlation between the induction of TmVIL genes and the downregulation of the floral repressor VRN2 similar to the VIN3/FLC and VIL1/FLM relationships (Fig. 1). Perhaps VIN3-related genes have similar roles both in Arabidopsis and in temperate wheat, but act on different target genes, possibly as a result of convergent evolution. Interestingly, the wheat gene TmVRN3 is homologous to FLOWERING LOCUS T (FT) of Arabidopsis, and TmVRN3 is repressed by TmVRN2 as FT is repressed by FLC,¹⁵ suggesting another similarity in the regulation of flowering time between Arabidopsis and temperate wheat (Fig. 1).Open in a separate windowFigure 1Proposed relationship of VIN3 family genes to the regulatory network controlling flowering time in response to environmental cues in Arabidopsis and diploid wheat (adapted from ref. ¹⁶).Although the PHD finger can be found in various eukaryotes, the VID is unique to plants. It is also noteworthy that VIN3-related genes can be found in various plant species, including rice, which does not have a vernalization response. It will be interesting to address whether the VIN3-related genes from various plant species are more broadly involved in relaying environmental signals to developmental programs.     

高等植物成花基因的研究

高等植物的成花可分为两个阶段：由茎顶端分生组织转变成花分生组织和花器官的形成。前者主要受成花计时基因的控制,而后一阶段主要由植物的同源（异型）框基因调控。本文综述了近年来对植物成花调控基因的研究,并着重对第一阶段成花基因的功能、它们间的相互作用和特点进行了总结。 Abstract:Plant flower can be divided into two phases——from stem apex meristem tissue into flower meristem tissue and floral apparatus.The flower time genes control the flower development and the homologous genes control flower apparatus identify.This paper summarizes recent studies on plant flower and emphasizes on the first phase flower control genes,theirs interaction and function,characteristic of the homologous genes.     

LEAFY Interacts with Floral Homeotic Genes to Regulate Arabidopsis Floral Development

In the leafy mutant of Arabidopsis, most of the lateral meristems that are fated to develop as flowers in a wild-type plant develop as inflorescence branches, whereas a few develop as abnormal flowers consisting of whorls of sepals and carpels. We have isolated several new alleles of leafy and constructed a series of double mutants with leafy and other homeotic mutants affecting floral development to determine how these genes interact to specify the developmental fate of lateral meristems. We found that leafy is completely epistatic to pistillata and interacts additively with agamous in early floral whorls, whereas in later whorls leafy is epistatic to agamous. Double mutants with leafy and either apetala1 or apetala2 showed a complete loss of the whorled phyllotaxy, shortened internodes, and suppression of axillary buds typical of flowers. Our results suggest that the products of LEAFY, APETALA1, and APETALA2 together control the differentiation of lateral meristems as flowers rather than as inflorescence branches.     

Identification of Soybean Genes Involved in Circadian Clock Mechanism and Photoperiodic Control of Flowering Time by In Silico Analyses

Glycine max is a photoperiodic short-day plant and the practical consequence of the response is latitude and sowing period limitations to commercial crops. Genetic and physiological studies using the model plants Arabidopsis thaliana and rice （Oryza sativa） have uncovered several genes and genetic pathways controlling the process, however information about the corresponding pathways in legumes is scarce. Data mining prediction methodologies, including multiple sequence alignment, phylogeneUc analysis, bioinformaUcs expression and sequence motif pattern identification, were used to identify soybean genes involved in day length perception and photoperiodic flowering induction. We have investigated approximately 330 000 sequences from open-access databases and have identified all bona fide central oscillator genes and circadian photoreceptors from A. thaliana in soybean sequence databases. We propose a working model for the photoperiodic control of flowering time in G. max, based on the identified key components. These results demonstrate the power of comparative genomics between model systems and crop species to elucidate the several aspects of plant physiology and metabolism.     

Comparison of Flowering Time Genes in Brassica Rapa, B. Napus and Arabidopsis Thaliana

The major difference between annual and biennial cultivars of oilseed Brassica napus and B. rapa is conferred by genes controlling vernalization-responsive flowering time. These genes were compared between the species by aligning the map positions of flowering time quantitative trait loci (QTLs) detected in a segregating population of each species. The results suggest that two major QTLs identified in B. rapa correspond to two major QTLs identified in B. napus. Since B. rapa is one of the hypothesized diploid parents of the amphidiploid B. napus, the vernalization requirement of B. napus probably originated from B. rapa. Brassica genes also were compared to flowering time genes in Arabidopsis thaliana by mapping RFLP loci with the same probes in both B. napus and Arabidopsis. The region containing one pair of Brassica QTLs was collinear with the top of chromosome 5 in A. thaliana where flowering time genes FLC, FY and CO are located. The region containing the second pair of QTLs showed fractured collinearity with several regions of the Arabidopsis genome, including the top of chromosome 4 where FRI is located. Thus, these Brassica genes may correspond to two genes (FLC and FRI) that regulate flowering time in the latest flowering ecotypes of Arabidopsis.     

Notch and Wingless Regulate Expression of Cuticle Patterning Genes

The cell surface receptor Notch is required during Drosophila embryogenesis for production of epidermal precursor cells. The secreted factor Wingless is required for specifying different types of cells during differentiation of tissues from these epidermal precursor cells. The results reported here show that the full-length Notch and a form of Notch truncated in the amino terminus associate with Wingless in S2 cells and in embryos. In S2 cells, Wingless and the two different forms of Notch regulate expression of Dfrizzled 2, a receptor of Wg; hairy, a negative regulator of achaete expression; shaggy, a negative regulator of engrailed expression; and patched, a negative regulator of wingless expression. Analyses of expression of the same genes in mutant N embryos indicate that the pattern of gene regulations observed in vitro reflects regulations in vivo. These results suggest that the strong genetic interactions observed between Notch and wingless genes during development of Drosophila is at least partly due to regulation of expression of cuticle patterning genes by Wingless and the two forms of Notch.