LysM蛋白在植物免疫中的作用

溶解素基序（LysM）是在多种蛋白质中普遍存在的结构域.植物LysM蛋白能够感知几丁质及其寡糖等分子配体，从而启动植物对病原菌的免疫反应.在水稻、拟南芥等植物免疫应答过程中，LysM蛋白作为一种重要的模式识别受体，通过不同形式的寡聚化，激活多种类受体胞质激酶及其下游的MAPK（mitogen activated protein kinase）级联反应传递信号.同时，蛋白质可逆磷酸化和蛋白质降解途径可以负调节LysM蛋白介导的防御信号转导.文章综述了植物免疫过程中LysM蛋白介导的信号转导分子机制.     

Ethylene signaling in rice

Ethylene regulates many aspects of growth, development and responses to environmental stresses in plants. Its signaling pathway has been established in model dicotyledonous plant Arabidopsis. However, its roles and signal transduction in monocotyledous rice plant remain largely unknown. In this review, we summarize the current advances in rice ethylene signaling studies and compare these with the results from Arabidopsis and other plants. Most of the components homologous to those in Arabidopsis ethylene signaling pathway have been found in rice, including five ethylene receptors, OsEIN2, OsEIL1, and OsERFs. Rice ethylene receptors are functionally more divergent than that of Arabidopsis. OsEIN2 and OsEIL1 display limited roles in regulation of rice ethylene responses compared with their Arabidopsis orthologs. ERF-like proteins OsERF1 and OsEBP-89 appear to be involved in rice ethylene signaling. However, whether they are activated through OsEIN2 and OsEIL1-mediated pathway needs further studies. Given that rice uses ethylene to control many processes that do not exist in Arabidopsis, it seems that new components or new mechanisms may exist in rice ethylene signaling pathway.     

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.     

ClpS is an essential component of the N-end rule pathway in Escherichia coli

The N-end rule states that the half-life of a protein is determined by the nature of its amino-terminal residue. Eukaryotes and prokaryotes use N-terminal destabilizing residues as a signal to target proteins for degradation by the N-end rule pathway. In eukaryotes an E3 ligase, N-recognin, recognizes N-end rule substrates and mediates their ubiquitination and degradation by the proteasome. In Escherichia coli, N-end rule substrates are degraded by the AAA + chaperone ClpA in complex with the ClpP peptidase (ClpAP). Little is known of the molecular mechanism by which N-end rule substrates are initially selected for proteolysis. Here we report that the ClpAP-specific adaptor, ClpS, is essential for degradation of N-end rule substrates by ClpAP in bacteria. ClpS binds directly to N-terminal destabilizing residues through its substrate-binding site distal to the ClpS-ClpA interface, and targets these substrates to ClpAP for degradation. Degradation by the N-end rule pathway is more complex than anticipated and several other features are involved, including a net positive charge near the N terminus and an unstructured region between the N-terminal signal and the folded protein substrate. Through interaction with this signal, ClpS converts the ClpAP machine into a protease with exquisitely defined specificity, ideally suited to regulatory proteolysis.     

Degradation of a cohesin subunit by the N-end rule pathway is essential for chromosome stability

Cohesion between sister chromatids is established during DNA replication and depends on a protein complex called cohesin. At the metaphase-anaphase transition in the yeast Saccharomyces cerevisiae, the ESP1-encoded protease separin cleaves SCC1, a subunit of cohesin with a relative molecular mass of 63,000 (Mr 63K). The resulting 33K carboxy-terminal fragment of SCC1 bears an amino-terminal arginine-a destabilizing residue in the N-end rule. Here we show that the SCC1 fragment is short-lived (t1/2 approximately 2 min), being degraded by the ubiquitin/proteasome-dependent N-end rule pathway. Overexpression of a long-lived derivative of the SCC1 fragment is lethal. In ubr1Delta cells, which lack the N-end rule pathway, we found a highly increased frequency of chromosome loss. The bulk of increased chromosome loss in ubr1Delta cells is caused by metabolic stabilization of the ESP1-produced SCC1 fragment. This fragment is the first physiological substrate of the N-end rule pathway that is targeted through its N-terminal residue. A number of yeast proteins bear putative cleavage sites for the ESP1 separin, suggesting other physiological substrates and functions of the N-end rule pathway.     

The N-end rule pathway as a nitric oxide sensor controlling the levels of multiple regulators

The conjugation of arginine to proteins is a part of the N-end rule pathway of protein degradation. Three amino (N)-terminal residues--aspartate, glutamate and cysteine--are arginylated by ATE1-encoded arginyl-transferases. Here we report that oxidation of N-terminal cysteine is essential for its arginylation. The in vivo oxidation of N-terminal cysteine, before its arginylation, is shown to require nitric oxide. We reconstituted this process in vitro as well. The levels of regulatory proteins bearing N-terminal cysteine, such as RGS4, RGS5 and RGS16, are greatly increased in mouse ATE1-/- embryos, which lack arginylation. Stabilization of these proteins, the first physiological substrates of mammalian N-end rule pathway, may underlie cardiovascular defects in ATE1-/- embryos. Our findings identify the N-end rule pathway as a new nitric oxide sensor that functions through its ability to destroy specific regulatory proteins bearing N-terminal cysteine, at rates controlled by nitric oxide and apparently by oxygen as well.     

水稻组蛋白单泛素化连接酶基因(OsHUB1)的克隆及其表达分析

对模式植物拟南芥的研究发现,AtHUB1基因参与调控植物对灰霉病的抗性.为了研究水稻的抗病机理,笔者利用同源搜索从水稻数据库中获得了目标基因的序列,并通过RT-PCR技术从水稻中克隆了组蛋白单泛素化连接酶基因,命名为OsHUB1.该片段包含1个2 655 bp的开放阅读框,编码了1个885氨基酸的多肽.与NCBI数据库的比对结果表明:OsHUB1的氨基酸序列与短柄草(Brachypodium distachyon)、葡萄(Vitis vinifera)、杨树(Populus tomentosa)、大豆(Glycine max)和拟南芥(Arabidopsis thaliana)的泛素E3连接酶的同源性分别为78%,68%,68%,67%和62%.这些不同来源的组蛋白单泛素化连接酶都含有一个高度保守的RING指结构域.半定量表达分析结果表明:OsHUB1基因能够被水杨酸(SA)和茉莉酸(JA)诱导表达,说明OsHUB1基因可能通过SA和JA介导的信号转导途径参与水稻的抗病反应.     

Sub1A is an ethylene-response-factor-like gene that confers submergence tolerance to rice

Most Oryza sativa cultivars die within a week of complete submergence--a major constraint to rice production in south and southeast Asia that causes annual losses of over US 1 billion dollars and affects disproportionately the poorest farmers in the world. A few cultivars, such as the O. sativa ssp. indica cultivar FR13A, are highly tolerant and survive up to two weeks of complete submergence owing to a major quantitative trait locus designated Submergence 1 (Sub1) near the centromere of chromosome 9 (refs 3, 4, 5-6). Here we describe the identification of a cluster of three genes at the Sub1 locus, encoding putative ethylene response factors. Two of these genes, Sub1B and Sub1C, are invariably present in the Sub1 region of all rice accessions analysed. In contrast, the presence of Sub1A is variable. A survey identified two alleles within those indica varieties that possess this gene: a tolerance-specific allele named Sub1A-1 and an intolerance-specific allele named Sub1A-2. Overexpression of Sub1A-1 in a submergence-intolerant O. sativa ssp. japonica conferred enhanced tolerance to the plants, downregulation of Sub1C and upregulation of Alcohol dehydrogenase 1 (Adh1), indicating that Sub1A-1 is a primary determinant of submergence tolerance. The FR13A Sub1 locus was introgressed into a widely grown Asian rice cultivar using marker-assisted selection. The new variety maintains the high yield and other agronomic properties of the recurrent parent and is tolerant to submergence. Cultivation of this variety is expected to provide protection against damaging floods and increase crop security for farmers.     

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.     

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。     

植物盐胁迫的信号传导途径

植物耐盐性研究具有重要意义.近年来,植物盐胁迫信号传导途径一直是植物耐盐性研究的热点.目前已阐明的盐胁迫信号传导途径有酵母和植物中的MAPK(mitogen-actirated protein kinase)途径、拟南芥中缓解离子胁迫的SOS(salt overIy sensitive)途径以及其他蛋白激酶参与的信号传导途径,其中包括钙依赖而钙调素不依赖的蛋白激酶、受体蛋白激酶、糖原合成酶的激酶和组蛋白激酶.因此,植物的耐盐性是个非常复杂的问题,可能是由多种信号分子参与的网络体系.大量转基因实验证明,信号传导途径中的某些组分可改善植物的耐盐性.因此,深入研究植物的盐胁迫信号传导是提高植物耐盐性的前提和基础.     

Cloning and expressional characterization of soybean GmLls1 gene

In higher plants, green leaf is a very important part involved in the photosynthesis process. Good develop-ment of the leaves is the guarantee of high yields and quality. Leaf senescence that occurs in the last stage of leaf development is a genetically p…     

A cytosolic trans-activation domain essential for ammonium uptake

Polytopic membrane proteins are essential for cellular uptake and release of nutrients. To prevent toxic accumulation, rapid shut-off mechanisms are required. Here we show that the soluble cytosolic carboxy terminus of an oligomeric ammonium transporter from Arabidopsis thaliana serves as an allosteric regulator essential for function; mutations in the C-terminal domain, conserved between bacteria, fungi and plants, led to loss of transport activity. When co-expressed with intact transporters, mutants inactivated functional subunits, but left their stability unaffected. Co-expression of two inactive transporters, one with a defective pore, the other with an ablated C terminus, reconstituted activity. The crystal structure of an Archaeoglobus fulgidus ammonium transporter (AMT) suggests that the C terminus interacts physically with cytosolic loops of the neighbouring subunit. Phosphorylation of conserved sites in the C terminus are proposed as the cognate control mechanism. Conformational coupling between monomers provides a mechanism for tight regulation, for increasing the dynamic range of sensing and memorizing prior events, and may be a general mechanism for transporter regulation.     

拟南芥SnRK2.2/2.3激酶参与调节镉胁迫响应的机制探究

为探究拟南芥SnRK2.2和SnRK2.3基因对Cd胁迫响应的分子机制. 以野生型（WT）、双突变体SnRK2.2/2.3、过表达SnRK2.2和过表达SnRK2.3的转基因植物为材料,研究SnRK2.2和SnRK2.3基因与Cd胁迫响应的关系.发现过表达两个基因可以提高拟南芥对Cd的耐受性,表现为可以减少Cd、丙二醛（MDA）及活性氧（ROS）的累积量,增加抗氧化酶CAT、POD和SOD的活性. qRT PCR结果显示在Cd胁迫下,两种过表达植株中铁转运蛋白IRT1和转录因子FIT、bHLH038和bHLH039表达水平受到明显抑制,ABA合成相关基因AAO3和NCED3的表达量显著上调.在Cd胁迫下,两种过表达植株中ABA含量显著高于WT和双突变体. 以上结果表明：拟南芥遭受Cd胁迫时,SnRK2.2和SnRK2.3基因通过下调IRT1基因表达从而减少植物对Cd的吸收,同时通过增加内源ABA含量来缓解Cd对植物的毒害.     

AhBG1转基因拟南芥的ABA敏感性和抗旱性研究

为探究花生基因AhBG1对拟南芥ABA敏感性和抗旱性的影响,以过表达AhBG1拟南芥为材料,检测其ABA敏感性及脱水处理下ABA质量分数、叶片失水率、干旱存活率及ABA稳态相关基因表达变化.结果表明:AhBG1是编码花生β-葡萄糖苷酶的家族成员,定位于细胞质;与野生型相比,AhBG1过表达拟南芥植株在干旱条件下体内AB...