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。     

Adaptation of photoperiodic control pathways produces short-day flowering in rice

The photoperiodic control of flowering is one of the important developmental processes of plants because it is directly related to successful reproduction. Although the molecular genetic analysis of Arabidopsis thaliana, a long-day (LD) plant, has provided models to explain the control of flowering time in this species, very little is known about its molecular mechanisms for short-day (SD) plants. Here we show how the photoperiodic control of flowering is regulated in rice, a SD plant. Overexpression of OsGI, an orthologue of the Arabidopsis GIGANTEA (GI) gene in transgenic rice, caused late flowering under both SD and LD conditions. Expression of the rice orthologue of the Arabidopsis CONSTANS (CO) gene was increased in the transgenic rice, whereas expression of the rice orthologue of FLOWERING LOCUS T (FT) was suppressed. Our results indicate that three key regulatory genes for the photoperiodic control of flowering are conserved between Arabidopsis, a LD plant, and rice, a SD plant, but regulation of the FT gene by CO was reversed, resulting in the suppression of flowering in rice under LD conditions.     

植物激素调控籽粒大小的研究进展

植物种子的大小和品质是影响农作物产量的主要因素之一,研究控制种子籽粒大小发育的相关因素,对提高农作物产量具有重要意义.近年通过分析种子发育缺陷突变体或QTL等分子遗传学的方法,发现许多控制种子发育的重要基因影响着种子的大小和产量.对模式植物拟南芥和水稻的研究发现,许多调控种子发育的功能基因通过整合到植物激素的代谢或信号转导途径起作用,说明植物激素在调控籽粒发育中发挥重要作用,但有关作用的分子机理及其遗传调控网络待阐明.该文以模式植物拟南芥和水稻种子发育研究为例,着重介绍植物激素调控种子籽粒大小调控的研究进展.     

非编码RNA调控心脏重构与再生

近年来, 越来越多的证据表明, 大量的非编码RNA(non-coding RNAs, ncRNAs)在基因的表达调控、细胞和机体的生理功能维持与病理环境调节方面都有重要作用, 其中主要包括微小RNA(microRNAs, miRNAs) 和长链非编码RNA(long non-coding RNAs, lncRNAs).心脏重构与再生是心血管疾病领域的关键问题, 其调控过程非常复杂, 包括表观遗传、转录、转录后及翻译水平的调控. 大量研究发现在转录后水平, miRNAs 通过负性调节靶标的表达调控心脏发育、疾病及再生进程. 近期研究揭示, lncRNAs 在心脏发育和疾病中具有潜在的作用, 可通过表观遗传、转录及转录后水平发挥作用. lncRNAs 已成为继miRNAs 之后的又一重要的调节性非编码RNA. 就非编码RNA 在心脏重构及再生进程中的调控作用进行综述.     

Sequence and analysis of chromosome 1 of the plant Arabidopsis thaliana

The genome of the flowering plant Arabidopsis thaliana has five chromosomes. Here we report the sequence of the largest, chromosome 1, in two contigs of around 14.2 and 14.6 megabases. The contigs extend from the telomeres to the centromeric borders, regions rich in transposons, retrotransposons and repetitive elements such as the 180-base-pair repeat. The chromosome represents 25% of the genome and contains about 6,850 open reading frames, 236 transfer RNAs (tRNAs) and 12 small nuclear RNAs. There are two clusters of tRNA genes at different places on the chromosome. One consists of 27 tRNA(Pro) genes and the other contains 27 tandem repeats of tRNA(Tyr)-tRNA(Tyr)-tRNA(Ser) genes. Chromosome 1 contains about 300 gene families with clustered duplications. There are also many repeat elements, representing 8% of the sequence.     

SERRATE coordinates shoot meristem function and leaf axial patterning in Arabidopsis

Leaves of flowering plants are determinate organs produced by pluripotent structures termed shoot apical meristems. Once specified, leaves differentiate an adaxial (upper) side specialized for light capture, and an abaxial (lower) side specialized for gas exchange. A functional relationship between meristem activity and the differentiation of adaxial leaf fate has been recognized for over fifty years, but the molecular basis of this interaction is unclear. In Arabidopsis thaliana, activity of the class I KNOX (KNOTTED1-like homeobox) genes SHOOTMERISTEMLESS (STM) and BREVIPEDICELLUS (BP) is required for meristem function but excluded from leaves, whereas members of the HD-Zip III (class III homeodomain leucine zipper) protein family function to promote both meristem activity and adaxial leaf fate. Here we show that the zinc-finger protein SERRATE acts in a microRNA (miRNA) gene-silencing pathway to regulate expression of the HD-Zip III gene PHABULOSA (PHB) while also limiting the competence of shoot tissue to respond to KNOX expression. Thus, SERRATE acts to coordinately regulate meristem activity and leaf axial patterning.     

microRNA-16 expression in HeLa cells is upregulated in cell-cycle and drug dependent manner

microRNAs are single-stranded, non-coding RNAs that regulate gene expression. The microRNA-16 family has been reported to be involved in cell-cycle regulation, which could also downregulate expression of multiple pro-proliferation genes. The present results demonstrated that miR-16 expression in HeLa cells increased when the cells were arrested during S-phase under methyl methanesulfate (MMS) treatment. This further resulted in downregulation of a target protein CDC25A, whereas miR-16 expression did not increase when HeLa cells were arrested during the MMS-treated G₀/G₁ or G₂/M phase. Furthermore, when HeLa cells were arrested during S-phase with hydroxyurea treatment, miR-16 expression did not increase. These results suggest that expression levels of microRNAs in mammalian cells are delicately regulated under variable cellular conditions.     

动物MicroRNAs的研究进展

MicroRNAs（miRNAs）是一类小的、内源的、非编码的RNA家族,其在转录后水平上对基因表达进行调控。nfiRNAs是在研究秀丽新小杆线虫（Caenorhabditis elegans）发育转变过程中发现的,最初称为stRNAs（small temporal RNA,小时序RNA）,但stRNAs只是miRNAs家族的一部分,随后在线虫、植物和哺乳动物中发现了miRNAs家族的数百个成员。动物miRNAs不仅在发育调控中起重要作用,还参与许多重要的生理过程。本文综述了动物中miRNAs的发现历程、生物学起源、作用机制、生物学功能、研究方法,并对动植物miRNAs的特点进行了比较。     

An Arabidopsis hAT-like transposase is essential for plant development

A significant proportion of the genomes of higher plants and vertebrates consists of transposable elements and their derivatives. Autonomous DNA type transposons encode a transposase that enables them to mobilize to a new chromosomal position in the host genome by a cut-and-paste mechanism. As this is potentially mutagenic, the host limits transposition through epigenetic gene silencing and heterochromatin formation. Here we show that a transposase from Arabidopsis thaliana that we named DAYSLEEPER is essential for normal plant growth; it shares several characteristics with the hAT (hobo, Activator, Tam3) family of transposases. DAYSLEEPER was isolated as a factor binding to a motif (Kubox1) present in the upstream region of the Arabidopsis DNA repair gene Ku70. This motif is also present in the upstream regions of many other plant genes. Plants lacking DAYSLEEPER or strongly overexpressing this gene do not develop in a normal manner. Furthermore, DAYSLEEPER overexpression results in the altered expression of many genes. Our data indicate that transposase-like genes can be essential for plant development and can also regulate global gene expression. Thus, transposases can become domesticated by the host to fulfil important cellular functions.     

SHATTERPROOF MADS-box genes control seed dispersal in Arabidopsis

The fruit, which mediates the maturation and dispersal of seeds, is a complex structure unique to flowering plants. Seed dispersal in plants such as Arabidopsis occurs by a process called fruit dehiscence, or pod shatter. Few studies have focused on identifying genes that regulate this process, in spite of the agronomic value of controlling seed dispersal in crop plants such as canola. Here we show that the closely related SHATTERPROOF (SHP1) and SHATTERPROOF2 (SHP2) MADS-box genes are required for fruit dehiscence in Arabidopsis. Moreover, SHP1 and SHP2 are functionally redundant, as neither single mutant displays a novel phenotype. Our studies of shp1 shp2 fruit, and of plants constitutively expressing SHP1 and SHP2, show that these two genes control dehiscence zone differentiation and promote the lignification of adjacent cells. Our results indicate that further analysis of the molecular events underlying fruit dehiscence may allow genetic manipulation of pod shatter in crop plants.     

Role of transposable elements in heterochromatin and epigenetic control

Heterochromatin has been defined as deeply staining chromosomal material that remains condensed in interphase, whereas euchromatin undergoes de-condensation. Heterochromatin is found near centromeres and telomeres, but interstitial sites of heterochromatin (knobs) are common in plant genomes and were first described in maize. These regions are repetitive and late-replicating. In Drosophila, heterochromatin influences gene expression, a heterochromatin phenomenon called position effect variegation. Similarities between position effect variegation in Drosophila and gene silencing in maize mediated by "controlling elements" (that is, transposable elements) led in part to the proposal that heterochromatin is composed of transposable elements, and that such elements scattered throughout the genome might regulate development. Using microarray analysis, we show that heterochromatin in Arabidopsis is determined by transposable elements and related tandem repeats, under the control of the chromatin remodelling ATPase DDM1 (Decrease in DNA Methylation 1). Small interfering RNAs (siRNAs) correspond to these sequences, suggesting a role in guiding DDM1. We also show that transposable elements can regulate genes epigenetically, but only when inserted within or very close to them. This probably accounts for the regulation by DDM1 and the DNA methyltransferase MET1 of the euchromatic, imprinted gene FWA, as its promoter is provided by transposable-element-derived tandem repeats that are associated with siRNAs.     

水蕨(Ceratopteris thalictroides)两条MADS-box基因的克隆与分析

MADS-box转录因子,作为一个大的基因家族,在植物生长发育过程中起重要作用,尤其是作为开花植物花器官形成的主要调控者.该基因家族在揭示进化方面也有着重大意义.为了探究MADS-box基因的进化,需要更多的非开花植物中MADS-box基因的信息.选取水蕨(Ceratopteris thalictroides)作为材料,用RACE方法对其MADS-box基因进行克隆与分析.在水蕨中克隆得到两条MADS-box基因,分别命名为CtMADS1和CtMADS2.分析显示:CtMADS1属于MIKC*分支,而CtMADS2属于MIKCc分支,水蕨的这2条MADS-box基因与开花植物的MADS-box基因有着很近的亲缘关系,现在维管植物最近的共同祖先中至少存在2条不同的花同源异形基因,即MADS-box基因.     

Association of dwarfism and floral induction with a grape 'green revolution' mutation

The transition from vegetative to reproductive growth is an essential process in the life cycle of plants. Plant floral induction pathways respond to both environmental and endogenous cues and much has been learnt about these genetic pathways by studying mutants of Arabidopsis. Gibberellins (GAs) are plant growth regulators important in many aspects of plant growth and in Arabidopsis they promote flowering. Here we provide genetic evidence that GAs inhibit flowering in grapevine. A grapevine dwarf mutant derived from the L1 cell layer of the champagne cultivar Pinot Meunier produces inflorescences along the length of the shoot where tendrils are normally formed. The mutated gene associated with the phenotype is a homologue of the wheat 'green revolution' gene Reduced height-1 (ref. 6) and the Arabidopsis gene GA insensitive (GAI). The conversion of tendrils to inflorescences in the mutant demonstrates that the grapevine tendril is a modified inflorescence inhibited from completing floral development by GAs.     

Regulation of microRNA on plant development and viral infection

THE FIRST MIRNA WAS IDENTIFIED IN C. ELEGANS AS EARLY AS IN 1993; THE IMPORTANCE OF MIRNAS, HOWEVER, IS RECOGNIZED ONLY RECENTLY AFTER THE DISCOVERY OF MIRNAS EXISTING UNIVERSALLY IN EUKARYOTIC ORGANISMS. THE SECOND MIRNA WAS IDENTIFIED IN 2000[1]. SINCE …     

Isolation and ectopic expression of a bamboo MADS-box gene

A cDNA named DIMADS18 was isolated from the young spikelets of the sweet bamboo, Dendrocalamus latiflorus by RACE. DNA sequence analysis showed that DIMADS18 was composed of full ORF and 3UTR, but without 5UTR. The cDNA contained 1039 nucleotides and encoded a putative protein of 249 amino acid residues. The gene displayed the structure of a typical plant MADS box gene, which consisted of an MADS domain, K domain, a short I region, and the C-terminal region. Phylogenetic analysis of plant MADS box genes based on amino acid sequences revealed that DlMADS18 was grouped into the AGAMOUS-LIKE 6 (AGL6)-like subfamily. It was most likely homologous to the OsMADS6 of rice (Oryza sativa), with 88% sequence identity for the entire amino acid sequences. The DlMADS18 also showed relatively high amino acid sequence identity (59%) to AGL6 ofArabidopsis thaliana. To study the functions of DlMADS18, DlMADS18 cDNA clone driven by the CaMV 35S promoter was transformed into Arabidopsis plants. Transgenic plants of DlMADS18 exhibited the phenotypes of curled leaves, dwarfism, and early flowering with clustered terminal flowers. These results indicated that DlMADS18 may probably be involved in controlling the flowering time of D.latiflorus.     

Identification of CRE1 as a cytokinin receptor from Arabidopsis

Cytokinins are a class of plant hormones that are central to the regulation of cell division and differentiation in plants. It has been proposed that they are detected by a two-component system, because overexpression of the histidine kinase gene CKI1 induces typical cytokinin responses and genes for a set of response regulators of two-component systems can be induced by cytokinins. Two-component systems use a histidine kinase as an environmental sensor and rely on a phosphorelay for signal transduction. They are common in microorganisms, and are also emerging as important signal detection routes in plants. Here we report the identification of a cytokinin receptor. We identified Arabidopsis cre1 (cytokinin response 1) mutants, which exhibited reduced responses to cytokinins. The mutated gene CRE1 encodes a histidine kinase. CRE1 expression conferred a cytokinin-dependent growth phenotype on a yeast mutant that lacked the endogenous histidine kinase SLN1 (ref. 10), providing direct evidence that CRE1 is a cytokinin receptor. We also provide evidence that cytokinins can activate CRE1 to initiate phosphorelay signalling.     

Analysis of the genome sequence of the flowering plant Arabidopsis thaliana

The flowering plant Arabidopsis thaliana is an important model system for identifying genes and determining their functions. Here we report the analysis of the genomic sequence of Arabidopsis. The sequenced regions cover 115.4 megabases of the 125-megabase genome and extend into centromeric regions. The evolution of Arabidopsis involved a whole-genome duplication, followed by subsequent gene loss and extensive local gene duplications, giving rise to a dynamic genome enriched by lateral gene transfer from a cyanobacterial-like ancestor of the plastid. The genome contains 25,498 genes encoding proteins from 11,000 families, similar to the functional diversity of Drosophila and Caenorhabditis elegans--the other sequenced multicellular eukaryotes. Arabidopsis has many families of new proteins but also lacks several common protein families, indicating that the sets of common proteins have undergone differential expansion and contraction in the three multicellular eukaryotes. This is the first complete genome sequence of a plant and provides the foundations for more comprehensive comparison of conserved processes in all eukaryotes, identifying a wide range of plant-specific gene functions and establishing rapid systematic ways to identify genes for crop improvement.     

AGO1基因对拟南芥叶边缘锯齿状发育的影响

在拟南芥和水稻中Argonaute(AGO)蛋白是RNA介导的沉默复合体(RISC)的核心组分,在植物叶极性的分化方面具有重要的调节作用。实验根据AGO1基因序列设计一对特异引物,提取野生型拟南芥RNA作为模板,采用反转录PCR方法扩增出AGO1基因,并插入到克隆载体pGEM-T中。筛选鉴定后将AGO1连接到植物表达载体pBI121上,构建起植物表达载体pBI121-AGO1。并且利用农杆菌介导的方法转化拟南芥,通过抗性筛选,获得转基因植株。然后对转基因植株进行表型分析及AGO1蛋白的RT-PCR检测。通过对转基因拟南芥表达分析发现,与野生型拟南芥相比超表达AGO1蛋白的转基因拟南芥叶片明显呈锯齿状,说明AGO1基因影响拟南芥叶片发育。