Effect of SPoT-mediated Stringent Response on Biofilm Formation,Stress Resistance and Quorum Sensing in Pseudomonas protegens SN15-2

Applied Biochemistry and Microbiology - The stringent response (SR) is crucial for the response of bacteria to nutrient deprivation and other stresses. Pseudomonas protegens SN15-2 is a...     

Helicobacter pylori: a Eubacterium Lacking the Stringent Response

Accumulation of 16S rRNA and production of guanosine polyphosphates (pppGpp and ppGpp) were studied during amino acid starvation in three wild-type strains of Helicobacter pylori. All strains exhibit a relaxed phenotype with respect to accumulation of 16S rRNA. This constitutes the first example of a wild-type eubacterium showing a relaxed phenotype. The guanosine polyphosphate levels do not rise as a result of amino acid starvation, as expected for relaxed organisms. However, in both growing and starved cells, basal levels of the two polyphosphates appeared to be present, demonstrating that the enzymatic machinery for guanosine polyphosphate production is present in this organism. These findings are discussed within the framework of the hypothesis that stringent control is a physiological control mechanism more important for the fitness of prokaryotes growing in the general environment than for those that inhabit protected niches.     

GSTs在植物非生物逆境胁迫中的作用

植物在生长过程中会面临各种各样的胁迫,为了自我保护,植物进化出了多种抵御胁迫的策略。植物谷胱甘肽-S-转移酶（glutathione-S-transferases,GSTs,EC2.5.1.18）可以催化亲核性的谷胱甘肽（glutathione,GSH）与各种亲电子外源化学物的结合反应,降低细胞体内活性氧（reactive oxygen species,ROS）水平,从而减轻非生物胁迫对植物的损伤。本文主要概述了GSTs在植物抗非生物胁迫的作用。     

植物响应低温胁迫的应答机制

介绍了植物响应低温胁迫的生理生化和分子机制及其信号转导途径的研究进展。并对今后这一领域研究前景作了展望和讨论。     

脱水素在植物低温胁迫响应中的作用

脱水素(dehydrin)是一类胚胎发育后期丰富蛋白(LEA.late embryogenesis abundant proteins),含有富含赖氨酸的K片段,属于具有高度热稳定性的亲水性蛋白,在植物脱水条件下能保护细胞内蛋白质和膜结构免受破坏.低温胁迫下,耐低温植物细胞内部会发生一系列的生理生化反应来抵御低温所造成的伤害.很多研究表明植物脱水素的表达和积累与多种双子叶植物(包括草本和木本植物)以及冬季栽培的禾本科植物品种(特别是小麦和大麦)的耐低温能力密切相关.本文对近年来国内外关于脱水素的结构、功能以及内源ABA(abscisie acid)含量、拟南芥CBF(C-repeat binding factor)同源转录激活因子、春化基因、光周期信号等对脱水素基因的表达调控机制进行综述.     

赤霉素信号在非生物胁迫中的作用及其调控机制研究进展

赤霉素(GA)能促进种子萌发和植物生长发育。近年来的研究表明赤霉素这一激素在植物响应非生物胁迫中同样发挥着重要的作用。植物通过调节GA生物合成、信号转导及其生物活性提高胁迫耐受性。综述了赤霉素在应对常见的几类非生物胁迫中所起的作用,分析了其合成、信号转导通路调控机制以及赤霉素与其他激素在响应非生物胁迫的关系。     

The Role of Antioxidant Systems in the Cold Stress Response of Escherichia coli

The response of aerobically grown Escherichia coli cells to the cold shock induced by the rapid lowering of growth temperature from 37 to 20°C was found to be basically the same as the oxidative stress response. The enhanced sensitivity of cells deficient in two superoxide dismutases, Mn-SOD and Fe-SOD, and the increased expression of the Mn-SOD gene, sodA, in response to cold stress were interpreted as both oxidative and cold stresses are due to a rise in the intracellular level of superoxide anion. The long-term cultivation of E. coli at 20°C was also accompanied by the typical oxidative stress response reactions—an enhanced expression of the Mn-SOD and catalase HPI genes and a decrease in the intracellular level of reduced glutathione (GSH) and in the GSH/GSSG ratio.     

The Role of Endogenous Abscisic Acid in the Response of Plants to Stress

When a continuous stream of warm air (38°C) was directedon to the leaves of dwarf bean seedlings they wilted and thengradually regained turgor. This process of adaptation was accompaniedby an increasing abscisic acid (ABA) level in the leaves andan increase in leaf resistance (R_L). It is suggested that theleaf-water deficit induced by the warm-air treatment causedthe increase in ABA level and that the latter was responsiblefor stimulating stomatal closure, enabling the plants to regainfull turgor. A similar type of adaptation, brought about byan increased level of ABA in the leaves, is believed to occurin tomato, dwarf bean, and wheat plants when they are flooded.Predictably, in rice, a species adapted to a flooded environment,seedlings showed no increase in ABA level as a result of flooding. It is proposed that adaptation may involve the formation ofan equilibrium between ABA and its conjugate form (i. e. theglucose ester). The ABA-conjugate was observed to disperse slowlyfrom leaves recovering from a water deficit and therefore itmay act as a metabolic ‘back-stop’, enabling the‘free’ ABA level to remain high for a period evenwhen the leaves have regained turgor. Abscisic acid appears to be responsible for alleviating theeffects of water stress in plants, making it possible for plantsto pass through periods of stress with little harm.     

植物激素在苔藓生长发育与逆境响应过程中的作用机制研究进展

植物激素是由植物自身代谢产生的一类从产生部位移动到作用部位发挥调控功能的微量小分子有机物质,在植物生长发育、响应环境胁迫过程中起到关键作用.苔藓植物作为早期登陆的非维管植物,处于陆生植物进化早期的阶段,具有许多不同于维管植物的形态和生理特征.大部分苔藓中普遍存在8种主要的植物激素及其衍生物(包括ABA、JA、ET、SA...     

Inorganic Polyphosphate in Escherichia coli: the Phosphate Regulon and the Stringent Response

Escherichia coli transiently accumulates large amounts of inorganic polyphosphate (polyP), up to 20 mM in phosphate residues (P_i), in media deficient in both P_i and amino acids. This transient accumulation is preceded by the appearance of nucleotides ppGpp and pppGpp, generated in response to nutritional stresses. Mutants which lack PhoB, the response regulator of the phosphate regulon, do not accumulate polyP even though they develop wild-type levels of (p)ppGpp when subjected to amino acid starvation. When complemented with a phoB-containing plasmid, phoB mutants regain the ability to accumulate polyP. PolyP accumulation requires high levels of (p)ppGpp independent of whether they are generated by RelA (active during the stringent response) or SpoT (expressed during P_i starvation). Hence, accumulation of polyP requires a functional phoB gene and elevated levels of (p)ppGpp. A rapid assay of polyP depends on its adsorption to an anion-exchange disk on which it is hydrolyzed by a yeast exopolyphosphatase.     

工业微生物的酸胁迫响应及其抵御策略

有机酸的积累在工业发酵过程中是一个较为普遍的现象,会导致发酵体系pH的降低,进而引起酸胁迫,限制细胞生长及目标产物的积累。针对这一问题,本文阐述了工业微生物应对酸胁迫所发生的生理变化,提出了微生物在酸性环境中可能的3种自我调节机制,概括总结了目前提高微生物酸耐受性的策略及各自的优缺点,指出了未来可能的发展方向,以期为提高工业微生物的酸耐受性提供思路。     

蛋白质的泛素化修饰在细胞应激反应中的作用

泛素是真核细胞内广泛存在的一种高度保守的蛋白质。在特定泛素化酶催化下实现的蛋白质泛素化修饰反应能够高选择性地降解细胞中的特定信号蛋白质,对维持细胞正常的生理功能具有非常重要的作用。另外,某些泛素化修饰反应也能够实现与蛋白质降解无关的功能调控作用。p53、NF-κB和GADD45α是在细胞应激损伤反应中具有广泛调控作用的信号蛋白,发生在这些分子上的泛素化修饰反应是它们发挥相关分子机制的重要基础。     

植物表皮蜡质参与干旱胁迫的反应机制

植物表皮是植物与外部环境直接接触的部位,包括具有立体网状结构的角质和填充其间并覆盖其上的蜡质。植物在适应外界环境的过程中,表皮蜡质形成了特殊的结构和复杂的化学组成。植物表皮蜡质最重要的功能是参与阻止植物非气孔性失水,提高植物对水分的利用效率,以实现对干旱环境的适应。干旱环境会导致植物表皮蜡质代谢的变化,这种变化最终通过调控基因表达来实现。目前已经发现了多个蜡质代谢相关基因参与了植物对干旱环境的适应,部分基因已经成功克隆并且用于改良农作物的抗旱性。但这些基因参与干旱响应的分子机制及其与ABA的关系并不很清楚。就植物适应水分胁迫而发生的包括蜡质组成和含量在内的代谢变化,以及该过程中所涉及的主要基因及其分子生物学研究进行综述。探讨表皮蜡质在植物适应干旱中的重要作用及其分子机制,可为农作物的抗旱育种提供新型的分子标记和重要靶基因,最终服务于农业生产实践。     

The Role of GIGANTEA Gene in Mediating the Oxidative Stress Response and in Arabidopsis

The Arabidopsis GIGANTEA (GI) gene has been shown to be involved in the regulation of the oxidative stress response; however, little is known about the mechanism by which GI gene regulates the oxidative stress response. We show here that enhanced tolerance of the gi-3 mutant to oxidative stress is associated, at least in part, with constitutive activation of superoxide dismutase (SOD) and ascorbate peroxidase (APX) genes. The gi-3 plants were more tolerant to parquart (PQ) or hydrogen peroxide (H₂O₂)-mediated oxidative stress than wild-type plants. Analyses of concentrations of endogenous H₂O₂ and superoxide anion radicals as well as lipid peroxidation revealed that enhanced tolerance of gi-3 plants to oxidative stress was not due to defects in the uptake of PQ or the sequestration of PQ from its site of action, and that the gi-3 mutation alleviated oxidative damage of plant cells from PQ stress. Moreover, the gi-3 mutant showed constitutive activation of cytosolic Cu/ZnSOD and plastidic FeSOD as well as cytosolic APX1 and stromal APX genes, which at least in part contributed to constitutive increases in activities of anti-oxidative enzymes SOD and APX, respectively. To our knowledge, we demonstrate, for the first time, that GI gene regulates the oxidative stress response, at least in part, through modulation of SOD and APX genes.     

The Role of Stress Fibers in the Shape Determination Mechanism of Fish Keratocytes

Crawling cells have characteristic shapes that are a function of their cell types. How their different shapes are determined is an interesting question. Fish epithelial keratocytes are an ideal material for investigating cell shape determination, because they maintain a nearly constant fan shape during their crawling locomotion. We compared the shape and related molecular mechanisms in keratocytes from different fish species to elucidate the key mechanisms that determine cell shape. Wide keratocytes from cichlids applied large traction forces at the rear due to large focal adhesions, and showed a spatially loose gradient associated with actin retrograde flow rate, whereas round keratocytes from black tetra applied low traction forces at the rear small focal adhesions and showed a spatially steep gradient of actin retrograde flow rate. Laser ablation of stress fibers (contractile fibers connected to rear focal adhesions) in wide keratocytes from cichlids increased the actin retrograde flow rate and led to slowed leading-edge extension near the ablated region. Thus, stress fibers might play an important role in the mechanism of maintaining cell shape by regulating the actin retrograde flow rate.     

The Stringent Response and Cell Cycle Arrest in Escherichia coli

The bacterial stringent response, triggered by nutritional deprivation, causes an accumulation of the signaling nucleotides pppGpp and ppGpp. We characterize the replication arrest that occurs during the stringent response in Escherichia coli. Wild type cells undergo a RelA-dependent arrest after treatment with serine hydroxamate to contain an integer number of chromosomes and a replication origin-to-terminus ratio of 1. The growth rate prior to starvation determines the number of chromosomes upon arrest. Nucleoids of these cells are decondensed; in the absence of the ability to synthesize ppGpp, nucleoids become highly condensed, similar to that seen after treatment with the translational inhibitor chloramphenicol. After induction of the stringent response, while regions corresponding to the origins of replication segregate, the termini remain colocalized in wild-type cells. In contrast, cells arrested by rifampicin and cephalexin do not show colocalized termini, suggesting that the stringent response arrests chromosome segregation at a specific point. Release from starvation causes rapid nucleoid reorganization, chromosome segregation, and resumption of replication. Arrest of replication and inhibition of colony formation by ppGpp accumulation is relieved in seqA and dam mutants, although other aspects of the stringent response appear to be intact. We propose that DNA methylation and SeqA binding to non-origin loci is necessary to enforce a full stringent arrest, affecting both initiation of replication and chromosome segregation. This is the first indication that bacterial chromosome segregation, whose mechanism is not understood, is a step that may be regulated in response to environmental conditions.