Assessing the redundancy of MADS-box genes during carpel and ovule development

Carpels are essential for sexual plant reproduction because they house the ovules and subsequently develop into fruits that protect, nourish and ultimately disperse the seeds. The AGAMOUS (AG) gene is necessary for plant sexual reproduction because stamens and carpels are absent from ag mutant flowers. However, the fact that sepals are converted into carpelloid organs in certain mutant backgrounds even in the absence of AG activity indicates that an AG-independent carpel-development pathway exists. AG is a member of a monophyletic clade of MADS-box genes that includes SHATTERPROOF1 (SHP1), SHP2 and SEEDSTICK (STK), indicating that these four genes might share partly redundant activities. Here we show that the SHP genes are responsible for AG-independent carpel development. We also show that the STK gene is required for normal development of the funiculus, an umbilical-cord-like structure that connects the developing seed to the fruit, and for dispersal of the seeds when the fruit matures. We further show that all four members of the AG clade are required for specifying the identity of ovules, the landmark invention during the course of vascular plant evolution that enabled seed plants to become the most successful group of land plants.     

SPL转录因子调控植物花发育及其分子机制研究进展

SPL(squamosa promoter-binding protein-like)转录因子是植物所特有的一类基因家族,广泛存在于绿色植物中,在植物生长发育中具有重要作用。花发育是植物生殖发育中最为重要的一个过程,涉及不同发育方式的转变,即开花决定、花的发端和花器官发生与发育。简要综述了SPL基因的结构与功能并着重阐述了SPL基因在植物花发育过程中的分子机制及生物学功能。最后总结出: SPL转录因子可直接或间接通过参与光周期途径,赤霉素途径及年龄途径来调控植物的开花时间; SPL基因可通过直接激活下游花分生组织特异基因,如LEAFY(LFY),从而调控植物的成花转变; SPL基因可通过与下游花器官特征基因相互作用来调控花器官及其育性的发育,如调控花序、花柄的长度与外形及花器官的大小; SPL基因可调控植物大小孢子发生及雌雄配子体发育。据拟南芥的相关研究结果,初步构绘出拟南芥开花调控中的分子机制。     

Functional characterization and mapping of two MADS box genes from peach (Prunus persica)

Previously an AGAMOUS gene homologue PpMADS4 and a FRUITFULL gene homologue PpMADS6 were isolated from peach (Prunus persica), and both genes were shown to express in the developing floral and fruits. To gain insight into their function, the two genes were constitutively expressed in Arabidopsis thaliana and their effects on plant growth and floral organ development were studied in this work. The transgenic plants all displayed early flowering and conversion of inflorescence to floral meristem. However, the two genes had different effects on the floral organ structures in A. thaliana. The transgenic plants overexpressing PpMADS4 displayed homeotic conversion of floral organs, and par- ticularly the perianth abscission was inhibited. The plants overexpressing PpMADS6 showed early flowering, produced higher number of carpels, petals, and stamens than nontransgenic plants, and pod shatter was prevented; significantly, the transgenic plants yielded more than one siliques from a single flower. A SSR molecular marker was developed for PpMADS4, and it was then assigned into the G5 linkage group of Prunus sp. Both PpMADS4 and PpMADS6 genes were located at the same region in the G5 linkage group. Our results showed the potential application of these two MADS box genes for crop and fruit tree improvement.     

Complexes of MADS-box proteins are sufficient to convert leaves into floral organs

Genetic studies, using floral homeotic mutants, have led to the ABC model of flower development. This model proposes that the combinatorial action of three sets of genes, the A, B and C function genes, specify the four floral organs (sepals, petals, stamens and carpels) in the concentric floral whorls. However, attempts to convert vegetative organs into floral organs by altering the expression of ABC genes have been unsuccessful. Here we show that the class B proteins of Arabidopsis, PISTILLATA (PI) and APETALA3 (AP3), interact with APETALA1 (AP1, a class A protein) and SEPALLATA3 (SEP3, previously AGL9), and with AGAMOUS (AG, a class C protein) through SEP3. We also show that vegetative leaves of triply transgenic plants, 35S::PI;35S::AP3;35S::AP1 or 35S::PI;35S::AP3;35S::SEP3, are transformed into petaloid organs and that those of 35S::PI;35S::AP3;35S::SEP3;35S::AG are transformed into staminoid organs. Our findings indicate that the formation of ternary and quaternary complexes of ABC proteins may be the molecular basis of the ABC model, and that the flower-specific expression of SEP3 restricts the action of the ABC genes to the flower.     

B and C floral organ identity functions require SEPALLATA MADS-box genes

Abnormal flowers have been recognized for thousands of years, but only in the past decade have the mysteries of flower development begun to unfold. Among these mysteries is the differentiation of four distinct organ types (sepals, petals, stamens and carpels), each of which may be a modified leaf. A landmark accomplishment in plant developmental biology is the ABC model of flower organ identity. This simple model provides a conceptual framework for explaining how the individual and combined activities of the ABC genes produce the four organ types of the typical eudicot flower. Here we show that the activities of the B and C organ-identity genes require the activities of three closely related and functionally redundant MADS-box genes, SEPALLATA1/2/3 (SEP1/2/3). Triple mutant Arabidopsis plants lacking the activity of all three SEP genes produce flowers in which all organs develop as sepals. Thus SEP1/2/3 are a class of organ-identity genes that is required for development of petals, stamens and carpels.     

植物AGAMOUS同源基因的表达调控

AGAMOUS基因（AG基因）是控制高等植物花器官发育的一类非常重要的基因.以拟南芥AG基因为例,重点综述了近20年来AG基因及其同源基因的结构、功能及与其它基因之间的调控关系的研究进展。在此基础上,对AG基因的表达和应用进行了探讨.     

Structural and expressional analysis of a cDNA that expresses predominantly in rice stamens

The development of stamen is an important stage during the sexual reproduction in higher plants. Studying the genes that predominantly or even specifically expressed in stamens will aid in undestanding the molecular mechanism of stamen development. The structure of a rice CHS-like gene (D5) which predominantly expressed in anthers has been analysised, showing high structural similarity with two other anther-specific genes (A1 and BA42) fromBrassica napus. Northern analysis also reveals that the three genes share a similar expression pattern and that the expression of D5 may relate to the early development of pollens. It is concluded that D5, A1 and BA42 represent a group of diverged CHS-like genes which are related to stamen development.     

Functional characterization and mapping of two MADS box genes from peach （Prunus persica）

Previously an AGAMOUS gene homologue PpMADS4 and a FRUITFULL gene homologue PpMADS6 were isolated from peach （Prunus persica）, and both genes were shown to express in the developing floral and fruits. To gain insight into their function, the two genes were constitutively expressed in Arabidopsis thaliana and their effects on plant growth and floral organ development were studied in this work. The transgenic plants all displayed early flowering and conversion of inflorescence to floral meristem. However, the two genes had different effects on the floral organ structures in A. thaliana. The transgenic plants overexpressing PpMADS4 displayed homeotic conversion of floral organs, and particularly the perianth abscission was inhibited. The plants overexpressing PpMADS6 showed early flowering, produced higher number of carpels, petals, and stamens than nontransgenic plants, and pod shatter was prevented; significantly, the transgenic plants yielded more than one siliques from a single flower. A SSR molecular marker was developed for PpMADS4, and it was then assigned into the G5 linkage group of Prunus sp. Both PpMADS4 and PpMADS6 genes were located at the same region in the G5 linkage group. Our results showed the potential application of these two MADS box genes for crop and fruit tree improvement.     

Tobacco floral homeotic gene homologues: partial sequence and expression pattern

Using PCR approach, three cDNA sequences, NTSQUA4, NTSQUA12 and NTSQUA15, were amplified from first_strand cDNAs of wild tobacco flower buds and identified as homologues for floral homeotic genes. All the three clones contained domains that a floral homeotic gene generally had, i.e. I domain, K domain and C_terminal domain except MADS_ box since the PCR primers were designed beyond this region. In addition, the amino acid sequences of them showed 50%-60% identity (70%-80% similarity) with the known floral organ identity class A gene AP1 and SQUA, possibly indicating that they are class A_like genes. NTSQUA4 and NTSQUA412 shared 95% identity in their amino acid sequence, while NTSQUA415 exhibited only 47% identity as compared with NTSQUA4 and NTSQUA12. Within tobacco flower, NTSQUA4 was expressed in sepals, petals and carpels, but not in stamens, while NTSQUA15 was expressed in every whorl of the flower. The possible functions of these genes are discussed.     

簸箕柳SPL基因家族分析

【目的】确定SPL基因家族在不同物种之间的选择性保留和丢失情况,为后续研究被子植物花发育提供参考。【方法】通过在拟南芥(Arabidopsis thaliana)、毛果杨(Populus trichocarpa)、簸箕柳(Salix suchowensis)、葡萄(Vitis vinifera)、番木瓜(Carica papaya)、水稻(Oryza sativa)6种被子植物基因组中查找SPL结构域,寻找6个物种的SPL同源序列。对所找到的SPL序列进行BLASTN比对鉴定同源基因类型。使用自编Perl脚本结合KaKs_Calculator计算SPL同源基因的非同义突变(K_a)以及同义突变(K_s)值,采用共线性分析确定该基因家族的复制和扩张方式。【结果】在6种被子植物基因组中,共发现120个SPL基因。根据种内和种间旁系同源、直系同源基因以及这些同源基因选择压的计算显示:杨柳科SPL同源基因最多,共有旁系同源基因24对,直系同源基因50对; 番木瓜没有旁系同源基因。6个物种中,木本植物比草本植物直系同源基因更多,双子叶植物比单子叶植物直系同源基因更多; 所有旁系同源和直系同源基因的K_a/K_s值均小于1。系统发育树的分析结果与基因同源性分析基本吻合,证明了这两种分析方法具有较高的可靠性。此次研究选取了簸箕柳同一植株上开花和不开花的枝条进行了转录组测序分析,差异表达分析发现了1个SPL基因(willow_GLEAN_10025160)在两种枝条的转录组中表达差异显著(P≤0.01),其在开花枝条中的表达量显著高于未开花枝条,该基因被选为SPL基因家族中参与簸箕柳开花调控的候选基因。【结论】通过对6个物种SPL基因家族的分析,发现6个物种中所有直系同源和旁系同源基因都经历了纯化选择(K_a/K_s<1),基因功能保守。这6个物种除了经历过全基因组复制事件,还发生过大规模的基因丢失或者通过其他方式产生的基因扩张,阐明了它们在进化历史上的复制事件及SPL基因在不同物种中的选择性保留与丢失情况,为进一步研究其在调控簸箕柳开花中的作用提供了有力证据。     

白魔芋开花过程内源激素动态变化

为探讨白魔芋开花过程中激素与雌、雄蕊成熟时间的关系,利用酶联免疫吸附法（ELISA）对白魔芋从佛焰苞形成前期到开花后期6个不同时期雄蕊和雌蕊中4种内源激素：生长素（IAA）、赤霉素（GA₃）、脱落酸（ABA）和玉米素（ZT）的质量比进行测定和分析.结果表明,IAA,GA₃,ABA和ZT 4种激素的质量比均呈现出不同的变化规律,IAA在雄蕊和雌蕊中均表现为下降—上升—下降的变化趋势;ABA表现出上升—下降—上升的变化趋势,与IAA的趋势相反;GA₃在整个过程中没有明显的变化规律,雄蕊在佛焰苞成形后期达到最大值,约为195 ng/g,而雌蕊GA₃的质量比晚于雄蕊达到最大值,雌蕊在开花前期才达到最大值,约为188 ng/g;ZT质量比的变化为先升后降、再升再降.在花芽形态分化,即雌、雄蕊成熟的关键时期,雌蕊中内源IAA,GA₃和ZT的质量比均高于雄蕊,且GA₃表现明显,说明较高浓度的IAA,GA₃和ZT在成熟过程中起促进作用,在同一过程中,雄蕊中ABA的质量比却高于雌蕊的,而雄蕊晚熟于雌蕊,表明较高浓度的ABA抑制雄蕊的成熟.ABA/IAA和ABA/ZT的比值呈现出与ABA相同的变化趋势,高浓度的ABA/IAA,ABA/ZT和ABA/GA₃均不利于雄蕊的成熟,进一步证明高浓度ABA是抑制雄蕊成熟的关键因子.     

The endothelial-cell-derived secreted factor Egfl7 regulates vascular tube formation

Vascular development is a complex but orderly process that is tightly regulated. A number of secreted factors produced by surrounding cells regulate endothelial cell (EC) differentiation, proliferation, migration and coalescence into cord-like structures. Vascular cords then undergo tubulogenesis to form vessels with a central lumen. But little is known about how tubulogenesis is regulated in vivo. Here we report the identification and characterization of a new EC-derived secreted factor, EGF-like domain 7 (Egfl7). Egfl7 is expressed at high levels in the vasculature associated with tissue proliferation, and is downregulated in most of the mature vessels in normal adult tissues. Loss of Egfl7 function in zebrafish embryos specifically blocks vascular tubulogenesis. We uncover a dynamic process during which gradual separation and proper spatial arrangement of the angioblasts allow subsequent assembly of vascular tubes. This process fails to take place in Egfl7 knockdown embryos, leading to the failure of vascular tube formation. Our study defines a regulator that controls a specific and important step in vasculogenesis.     

Efp targets 14-3-3 sigma for proteolysis and promotes breast tumour growth

Oestrogen exerts its influence on target organs through activating oestrogen receptors (ERs) and regulating downstream genes by means of their oestrogen-responsive elements. Efp, a target gene product of ER alpha, is a member of the RING-finger B-box coiled-coil (RBCC) motif family. Efp is predominantly expressed in various female organs as well as in breast cancers, and is thought to be essential for oestrogen-dependent cell proliferation and organ development Efp-disrupted mice display underdeveloped uteri and reduced oestrogen responsiveness. Here we show that Efp is a RING-finger-dependent ubiquitin ligase (E3) that targets proteolysis of 14-3-3 sigma, a negative cell cycle regulator that causes G2 arrest. We demonstrate that tumour growth of breast cancer MCF7 cells implanted in female athymic mice is reduced by treatment with antisense Efp oligonucleotide. Efp-overexpressing MCF7 cells in ovariectomized athymic mice generate tumours in the absence of oestrogen. Loss of Efp function in mouse embryonic fibroblasts results in an accumulation of 14-3-3 sigma, which is responsible for reduced cell growth. These data provide an insight into the cell-cycle machinery and tumorigenesis of breast cancer by identifying 14-3-3 sigma as a target for proteolysis by Efp, leading to cell proliferation.     

Maternal regulation of zerknüllt: a homoeobox gene controlling differentiation of dorsal tissues in Drosophila

The homoeobox gene zerknüllt (zen) plays an important role in the differentiation of dorsal tissues during Drosophila development. zen- embryos show transformations in the dorsal-most regions of the fate map, and lack several tissues that normally derive from these regions, including the amnioserosa and optic lobe. zen displays a simple dorsal on/ventral off pattern as early as cleavage cycle 10-11 (ref. 2). We have prepared a polyclonal antibody against a full-length zen protein, and used this to examine its pattern of expression in mutants that disrupt dorsal-ventral polarity. Most or all of the maternally expressed genes that are involved in this process have been previously identified and fall into two classes, so called 'dorsalizers' and 'ventralizers' (see refs 4-7, reviewed in ref. 8). On the basis of our analysis of zen expression in each of these maternal mutants we propose that one or more of the dorsalizing genes encodes a repressor which inhibits the expression of zen in ventral regions of developing embryos. The ventralizing gene cactus might play an important role in restricting the activity of this repressor to ventral regions, thereby permitting the activation of zen in those dorsal tissues where its function is critically required.     

宁夏枸杞愈伤组织器官发生和体细胞胚发生过程中过氧化物酶和酸性磷酸酶同工酶的研究

利用已建立的宁夏枸杞（Ｌｙｃｉｕｍ ｂａｒｂａｒｕｍ Ｌ．）叶愈伤组织器官发生和体细胞胚发生体系,比较研究了两条离体再生途径早期阶段愈伤组织的生长特性、过氧化物酶（ＰＯＤ）和酸性磷酸酶同工酶的活性及酶谱的变化。结果表明：（１）与继代愈伤组织的“Ｓ”形生长曲线不同,器官发生和体细胞胚发生过程的愈伤组织生长延迟期不明显,且第３ｄ后一直处于指数生长期,培养后期器官发生的愈伤组织生长速率快于体细胞胚发生;