黄瓜离体子叶节花芽和营养芽分化中CFL基因的表达

CFL基因是从黄瓜中克隆到的拟南芥LEAFY(LFY)同源基因.以离体黄瓜子叶培养物成花为实验体系,利用mRNA原位杂交技术对CFL基因在花芽和营养芽分化过程中的时空表达进行了分析.结果如下:在花芽分化过程中,CFL基因在花原基形成、花器官原基分化及各轮花器官形成之初强表达,在花器官形成以后表达减弱或不表达;在营养芽分化过程中,CFL基因在分生组织、叶原基和幼叶中有明显表达,在成熟组织中不表达.结果说明CFL基因的表达在黄瓜子叶节花芽和营养芽分化中原基的分化形成是必需的.结果提示CFL基因可能参与细胞分裂调控和启动、营养性分生组织向花分生组织转变等过程.     

Sucrose treatment alters floral induction and development in vitro in gloxinia

Previous studies have shown that Cucumber-FLO-LFY (CFL) overexpression significantly promotes early flowering without a gibberellin (GA₃) supplement in gloxinia (Sinningia speciosa), suggesting that CFL can serve functionally as a LEAFY homolog. In the present study, different sucrose concentrations were applied to the culture medium to investigate the effects of sucrose on the development of excised flower buds and the regeneration of floral buds from sepals in wild-type and 35S::CFL gloxinia lines. The results showed that floral buds were formed directly from sepal explants without prior formation of shoots and leaves in 35S::CFL gloxinia lines when 2% w/v sucrose was added. Conversely, 0% or 5% w/v sucrose inhibited the generation of flower buds from sepals and the opening of flowers. Semi-quantitative PCR also showed that a medium with 5% w/v sucrose significantly inhibited MADS-box gene expression in wild type and much less significantly in 35S::CFL gloxinia. These data indicate that sucrose, as the main carbohydrate transported in floral organs, is a significant promoter of flower induction and maturity.     

黄瓜中LFY同源基因CFL的克隆和分析

ＬＦＹ同源基因在高等植物花分生组织的发生中发挥着重要的作用。克隆了黄瓜（ Ｃｕｃｕｍｉｓｓａｔｉｖｕｓ Ｌ．） 中的ＬＦＹ同源基因ＣＦＬ,Ｓｏｕｔｈｅｒｎ 杂交的结果显示它在黄瓜基因组中为单拷贝基因,Ｎｏｒｔｈｅｒｎ 杂交结果显示它主要在花芽和幼叶中表达。讨论了ＣＦＬ基因在黄瓜开花和营养生长中可能发挥的作用     

Cloning and Analysis of CFL-A LFY-like Gene from Cucumber

LFY and LFY-like genes have been shown to control the initiation of floral meristems in higher plants. The homologous eDNA of LFY, CFL, were cloned from cucumber ( Cucumis sativus L. ). Southern blot analysis showed it was a single copy gene in the cucumber genome. Northern blot analysis showed that it expressed in the floral buds and young leaves. The possible role of CFL in the floral and vegetative development of cucumber plant was discussed.     

拟南芥LEAFY基因在花发育中的网络调控及其生物学功能

重点综述了拟南芥花分生组织特征基因——LEAFY（LFY）基因及其同源基因在花发育中的网络调控及其生物学功能。LFY基因广泛表达于高等植物的营养性和生殖性组织。LFY基因需要与其他基因相互作用,並且表达量达到一定水平时才能促进成花。LFY基因处于成花调控网络的关键位置,不仅调控开花时间和花转变,而且在花序和花的发育中也起重要作用。碳源、植物激素等因子直接或间接地影响LFY基因的表达和作用。提示通过掌握LFY基因的表达调控规律进一步探讨成花机理的可行性。 Abstract:Recent research progress on regulation network and biological roles of LFY gene in Arabidopsis thaliana and its homologue genes in floral development are reviewed emphatically in the present paper.LFY gene expresses widely in both vegetative and reproductive tissues in different higher plants,therefore investigation on role of LFY gene on flowering is of general significance.LFY gene plays an important role to promote flower formation by interaction and coordination with other genes,such as TFL,EMF,AP1,AP2,CAL,FWA,FT,AP3,PI,AG,UFO,CO,LD,GA1 etc,and a critical level of LFY expression is essential.LFY gene not only controls flowering-time and floral transition,but also plays an important role in inflorescence and floral organ development.It was situated at the central site in gene network of flowering regulation,positively or negatively regulates the level or activities of flowering-related genes.Some physiological factors,such as carbon sources,phytohormones,affect directly or indirectly the expression and actions of LFY gene.This indicates that level of LFY expression can also be regulated with physiological methods.It is probable that we can explain the principal mechanism of flowering by regulation network of LFY gene.     

Negative regulation of the Arabidopsis homeotic gene AGAMOUS by the APETALA2 product.

We characterized the distribution of AGAMOUS (AG) RNA during early flower development in Arabidopsis. Mutations in this homeotic gene cause the transformation of stamens to petals in floral whorl 3 and of carpels to another ag flower in floral whorl 4. We found that AG RNA is present in the stamen and carpel primordia but is undetectable in sepal and petal primordia throughout early wild-type flower development, consistent with the mutant phenotype. We also analyzed the distribution of AG RNA in apetela2 (ap2) mutant flowers. AP2 is a floral homeotic gene that is necessary for the normal development of sepals and petals in floral whorls 1 and 2. In ap2 mutant flowers, AG RNA is present in the organ primordia of all floral whorls. These observations show that the expression patterns of the Arabidopsis floral homeotic genes are in part established by regulatory interactions between these genes.     

Specific expression of the AGL1 MADS-box gene suggests regulatory functions in Arabidopsis gynoecium and ovule development

Several members of the MADS-box gene family have been shown to be important regulators of flower development, controlling such well-studied early events as the formation of the floral meristem and the specification of floral organ identity. Other floral-specific MADS-box genes, of as yet unknown function, have been isolated by homology and are proposed to be part of a regulatory hierarchy controlling flower development. Some of these genes might regulate later aspects of flower development, such as development of individual floral organs, which is less well studied at the molecular level. This paper presents a detailed analysis of the expression pattern of one such gene from Arabidopsis , AGL1 , using RNA in situ hybridization. It is found that AGL1 is specifically expressed in particular regions of the gynoecium and ovule, only during and after floral development stage 7. AGL1 expression at the tip of the growing carpel primordia, along the margins of the ovary valves in developing and mature gynoecia and in specific regions of developing and mature ovules provides important insights into the possible roles of AGL1 . It is proposed that AGL1 may have regulatory functions in the structural definition and/or function of the valve margins, in axis maintenance during ovule development, in nutritional supply to the growing ovule and embryo sac, and in pollen tube guidance. In the floral homeotic mutants ag-1 , ap3-3 and ap2-2 , AGL1 mRNA is expressed in an organ-dependent manner, suggesting that AGL1 is a carpel-specific gene and as such ultimately depends upon the carpel identity gene AG for proper gene expression.     

Eucalyptus has a functional equivalent of the Arabidopsis floral meristem identity gene LEAFY

Two genes cloned from Eucalyptus globulus, Eucalyptus LeaFy (ELF1 and ELF2), have sequence homology to the floral meristem identity genes LEAFY from Arabidopsis and FLORICAULA from Antirrhinum. ELF1 is expressed in the developing eucalypt floral organs in a pattern similar to LEAFY while ELF2 appears to be a pseudo gene. ELF1 is expressed strongly in the early floral primordium and then successively in the primordia of sepals, petals, stamens and carpels. It is also expressed in the leaf primordia and young leaves and adult and juvenile trees.The ELF1 promoter coupled to a GUS reporter gene directs expression in transgenic Arabidopsis in a temporal and tissue-specific pattern similar to an equivalent Arabidopsis LEAFY promoter construct. Strong expression is seen in young flower buds and then later in sepals and petals. No expression was seen in rosette leaves or roots of flowering plants or in any non-flowering plants grown under long days. Furthermore, ectopic expression of the ELF1 gene in transgenic Arabidopsis causes the premature conversion of shoots into flowers, as does an equivalent 35S-LFY construct. These data suggest that ELF1 plays a similar role to LFY in flower development and that the basic mechanisms involved in flower initiation and development in Eucalyptus are similar to those in Arabidopsis.     

Arabidopsis thaliana (L.) Heynh. as a model object for studying genetic control of morphogenesis

A vast amount of information on the genetic control of plant development has been obtained in Arabidopsis thaliana with classical genetic and molecular biological methods. The genes involved in multistep regulation of floral morphogenesis have been identified. The formation of floral meristem is controlled by the LEAFY (LFY), UNUSUAL FLORAL ORGANS (UFO), APETALA1 (AP1), and APETALA2 (AP2) genes. Studies of the abruptus and bractea recessive monogenic mutants from the collection of the Department of Genetics and Selection, Moscow State University, showed that the ABRUPTUS (ABR) and BRACTEA (BRA) genes also play an important role in inflorescence differentiation. The ABR gene controls the early formation of organ primordia on the inflorescence and the formation of floral organ primordia after floral initiation. Further differentiation of inflorescence organ primordia in vegetative or generative organs depends on the activity of the LFY gene, and floral organ identity is determined by the homeotic genes. Presumably, the major function of the ABR gene is to determine the auxin polar transport. The BRA gene suppresses the development of bracts on the inflorescence and constrains cell division at the base of primordia of rosette and cauline leaves.     

Structural basis for LEAFY floral switch function and similarity with helix-turn-helix proteins

The LEAFY (LFY) protein is a key regulator of flower development in angiosperms. Its gradually increased expression governs the sharp floral transition, and LFY subsequently controls the patterning of flower meristems by inducing the expression of floral homeotic genes. Despite a wealth of genetic data, how LFY functions at the molecular level is poorly understood. Here, we report crystal structures for the DNA-binding domain of Arabidopsis thaliana LFY bound to two target promoter elements. LFY adopts a novel seven-helix fold that binds DNA as a cooperative dimer, forming base-specific contacts in both the major and minor grooves. Cooperativity is mediated by two basic residues and plausibly accounts for LFY's effectiveness in triggering sharp developmental transitions. Our structure reveals an unexpected similarity between LFY and helix-turn-helix proteins, including homeodomain proteins known to regulate morphogenesis in higher eukaryotes. The appearance of flowering plants has been linked to the molecular evolution of LFY. Our study provides a unique framework to elucidate the molecular mechanisms underlying floral development and the evolutionary history of flowering plants.     

Cloning and characterization of a FLORICAULA/LEAFY ortholog, PFL, in polygamous papaya

The homologous genes FLORICAULA （FLO） in Antirrhinum and LEAFY （LFY） in Arabidopsis are known to regulate the initiation of flowering in these two distantly related plant species. These genes are necessary also for the expression of downstream genes that control floral organ identity. We used Arabidopsis LFY cDNA as a probe to clone and sequence a papaya ortholog of LFY, PFL. It encodes a protein that shares 61% identity with the Arabidopsis LFY gene and 71% identity with the LFY homologs of the two woody tree species： California sycamore （Platanus racemosa） and black cottonwood （Populus trichocarpa）. Despite the high sequence similarity within two conserved regions, the N-terminal proline-rich motif in papaya PFL differs from other members in the family. This difference may not affect the gene function of papaya PFL, since an equally divergent but a functional LFY ortholog NEEDLY of Pinus radiata has been reported. Genomic and BAC Southern analyses indicated that there is only one copy of PFL in the papaya genome. In situ hybridization experiments demonstrated that PFL is expressed at a relatively low level in leaf primordia, but it is expressed at a high level in the floral meristem. Quantitative PCR analyses revealed that PFL was expressed in flower buds of all three sex types - male, female, and hermaphrodite with marginal difference between hermaphrodite and unisexual flowers. These data suggest that PFL may play a similar role as LFY in flower development and has limited effect on sex differentiation in papaya.     

UFO in the Arabidopsis inflorescence apex is required for floral-meristem identity and bract suppression

The UNUSUAL FLORAL ORGANS (UFO) gene of Arabidopsis encodes an F-box protein required for the determination of floral-organ and floral-meristem identity. Mutation of UFO leads to dramatic changes in floral-organ type which are well-characterized whereas inflorescence defects are more subtle and less understood. These defects include an increase in the number of secondary inflorescences, nodes that alternate between forming flowers and secondary inflorescences, and nodes in which a single flower is subtended by a bract. Here, we show how inflorescence defects correlate with the abnormal development of floral primordia and establish a temporal requirement for UFO in this process. At the inflorescence apex of ufo mutants, newly formed primordia are initially bract-like. Expression of the floral-meristem identity genes LFY and AP1 are confined to a relatively small adaxial region of these primordia with expression of the bract-identity marker FIL observed in cells that comprise the balance of the primordia. Proliferation of cells in the adaxial region of these early primordia is delayed by several nodes such that primordia appear “chimeric” at several nodes, having visible floral and bract components. However, by late stage 2 of floral development, growth of the bract generally ceases and is overtaken by development of the floral primordium. This abnormal pattern of floral meristem development is not rescued by expression of UFO from the AP1 promoter, indicating that UFO is required prior to AP1 activation for normal development of floral primordia. We propose that UFO and LFY are jointly required in the inflorescence meristem to both promote floral meristem development and inhibit, in a non-cell autonomous manner, growth of the bract.Shelley R. Hepworth and Jennifer E. Klenz contributed equally to this work.     

A novel role of BELL1-like homeobox genes, PENNYWISE and POUND-FOOLISH, in floral patterning

Flowers are determinate shoots comprised of perianth and reproductive organs displayed in a whorled phyllotactic pattern. Floral organ identity genes display region-specific expression patterns in the developing flower. In Arabidopsis, floral organ identity genes are activated by LEAFY (LFY), which functions with region-specific co-regulators, UNUSUAL FLORAL ORGANS (UFO) and WUSCHEL (WUS), to up-regulate homeotic genes in specific whorls of the flower. PENNYWISE (PNY) and POUND-FOOLISH (PNF) are redundant functioning BELL1-like homeodomain proteins that are expressed in shoot and floral meristems. During flower development, PNY functions with a co-repressor complex to down-regulate the homeotic gene, AGAMOUS (AG), in the outer whorls of the flower. However, the function of PNY as well as PNF in regulating floral organ identity in the central whorls of the flower is not known. In this report, we show that combining mutations in PNY and PNF enhance the floral patterning phenotypes of weak and strong alleles of lfy, indicating that these BELL1-like homeodomain proteins play a role in the specification of petals, stamens and carpels during flower development. Expression studies show that PNY and PNF positively regulate the homeotic genes, APETALA3 and AG, in the inner whorls of the flower. Moreover, PNY and PNF function in parallel with LFY, UFO and WUS to regulate homeotic gene expression. Since PNY and PNF interact with the KNOTTED1-like homeodomain proteins, SHOOTMERISTEMLESS (STM) and KNOTTED-LIKE from ARABIDOPSIS THALIANA2 (KNAT2) that regulate floral development, we propose that PNY/PNF-STM and PNY/PNF-KNAT2 complexes function in the inner whorls to regulate flower patterning events.