Characterization of multiple regulatory networks and responses to environmental signals in Pseudomonas syringae during its association with plants

Pseudomonas syringae is a model bacterial plant pathogen that is adapted for growth and survival on leaf surfaces and in the leaf interior of its host plants. P. syringae likely experiences distinct environmental conditions in different phases of its interaction with plants. In this study, we used global transcriptome profiling of P. syringae pv. syringae B728a to analyze genes and traits that were responsive to growth and survival on the leaf surface versus in the leaf apoplast. We found that the epiphytic environment specifically favors active relocation via flagellar motility, swarming motility, chemosensing, and chemotaxis, whereas the apoplastic environment favors traits contributing to virulence including the synthesis of two phytotoxins and syingolin A as well as the degradation of an alternative amino acid that suppresses virulence. Through comparing the transcriptomes of in planta cells to those of cells exposed to various stresses in culture media, we found that water limitation is a major stress that limits B728a growth and survival in these leaf habitats. P. syringae can adapt to water stress by the production of a potent compatible solute, trehalose. Distinct P. syringae strains vary in their ability to tolerate water stress, possibly due, in part, to differences in the production or regulation of trehalose. To investigate this possibility, we compared the relative contribution of the trehalose biosynthetic pathways to trehalose synthesis in two closely related P. syringae strains B728a and DC3000 and characterized an apparent interdependency between these pathways. Our data showed that, of the two trehalose biosynthesis pathways, only one was required for trehalose production in B728a whereas both were needed in DC3000, and moreover that differences in trehalose production may help explain differences in their water stress tolerance. Lastly, to understand the contribution of distinct regulators to fitness and pathogenicity of P. syringae, we performed a transcriptome analysis of B728a and mutants lacking each of nine regulators, including quorum-sensing regulators (AhlR and AefR), global regulators (GacS, SalA and RetS), and alternative sigma factors (RpoN, AlgU, RpoS, and HrpL), with cells recovered from the surface and interior of bean leaves as well as exposed to various environmental stresses. Our data showed that AhlR and AefR had negligible roles during B728a leaf colonization, whereas GacS and SalA had major roles. GacS/SalA formed a large regulatory network with both plant signal-dependent and plant signal-independent branches. RetS functioned almost exclusively to repress secondary metabolite genes when B728a cells were not in the leaf environment. Among the alternative sigma factors, RpoN influenced the majority of the genome whereas AlgU influenced a large number and RpoS a small number of genes, with plant signals strongly attenuating RpoN activation of the AlgU-regulated genes. Lastly, HrpL influenced very few genes in planta, due primarily to suppression by GacS and SalA. Collectively, our results highlight the role of these regulators during P. syringae colonization of leaves and the central importance of signals in the leaf environment on their regulation

Glycine Betaine Catabolism Contributes to Pseudomonas syringae Tolerance to Hyperosmotic Stress by Relieving Betaine-Mediated Suppression of Compatible Solute Synthesis

Many bacteria can accumulate glycine betaine for osmoprotection and catabolize it as a growth substrate, but how they regulate these opposing roles is poorly understood. In Pseudomonas syringae B728a, expression of the betaine catabolism genes was reduced by an osmotic upshift to an intermediate stress level, consistent with betaine accumulation, but was increased by an upshift to a high stress level, as confirmed by an accompanying increase in degradation of radiolabeled betaine. Deletion of the gbcAB betaine catabolism genes reduced osmotolerance at a high osmolarity, and this reduction was due to the relief of betaine-mediated suppression of compatible solute synthesis. This conclusion was supported by the findings that, at high osmolarity, the ΔgbcAB mutant accumulated high betaine levels and low endogenous solutes and exhibited reduced expression of the solute synthesis genes. Moreover, the ΔgbcAB mutant and a mutant deficient in the synthesis of the compatible solutes NAGGN and trehalose exhibited similar reductions in osmotolerance and also in fitness on bean leaves. Activation of betaine catabolism at high osmotic stress resulted, in part, from induction of gbdR, which encodes the transcriptional activator GbdR. Betaine catabolism was subject to partial repression by succinate under hyperosmotic stress conditions, in contrast to strong repression in the absence of stress, suggesting that betaine functions both in nutrition and as an intracellular signal modulating solute synthesis under hyperosmotic stress conditions. Collectively, these results begin to provide a detailed mechanistic understanding of how P. syringae transitions from reliance on exogenously derived betaine to the use of endogenous solutes during adaptation to hyperosmotic conditions

Recent advances and perspectives for Zn-based batteries: Zn anode and electrolyte

Zn-based batteries have attracted extensive attention due to their high theoretical energy density, safety, abundant resources, environmental friendliness, and low cost. They are a new energy storage and conversion technology with significant development potential and have been widely used in renewable energy and portable electronic devices. Considerable attempts have been devoted to improving the performance of Zn-based batteries. Specifically, battery cycle life and energy efficiency can be improved by electrolyte modification and the construction of highly efficient rechargeable Zn anodes. This review compiles the progress of the research related to Zn anodes and electrolytes, especially in the last five years. This review will introduce fundamental concepts, summarize recent development, and inspire further systematic research for high-performance Zn-based batteries in the future

Physiological and Transcriptional Responses to Osmotic Stress of Two Pseudomonas syringae Strains That Differ in Epiphytic Fitness and Osmotolerance

The foliar pathogen Pseudomonas syringae is a useful model for understanding the role of stress adaptation in leaf colonization. We investigated the mechanistic basis of differences in the osmotolerance of two P. syringae strains, B728a and DC3000. Consistent with its higher survival rates following inoculation onto leaves, B728a exhibited superior osmotolerance over DC3000 and higher rates of uptake of plant-derived osmoprotective compounds. A global transcriptome analysis of B728a and DC3000 following an osmotic upshift demonstrated markedly distinct responses between the strains; B728a showed primarily upregulation of genes, including components of the type VI secretion system (T6SS) and alginate biosynthetic pathways, whereas DC3000 showed no change or repression of orthologous genes, including downregulation of the T3SS. DC3000 uniquely exhibited improved growth upon deletion of the biosynthetic genes for the compatible solute N-acetylglutaminylglutamine amide (NAGGN) in a minimal medium, due possibly to NAGGN synthesis depleting the cellular glutamine pool. Both strains showed osmoreduction of glnA1 expression, suggesting that decreased glutamine synthetase activity contributes to glutamate accumulation as a compatible solute, and both strains showed osmoinduction of 5 of 12 predicted hydrophilins. Collectively, our results demonstrate that the superior epiphytic competence of B728a is consistent with its strong osmotolerance, a proactive response to an osmotic upshift, osmoinduction of alginate synthesis and the T6SS, and resiliency of the T3SS to water limitation, suggesting sustained T3SS expression under the water-limited conditions encountered during leaf colonization

Transcriptional Analysis of the Global Regulatory Networks Active in Pseudomonas syringae during Leaf Colonization

The plant pathogen Pseudomonas syringae pv. syringae B728a grows and survives on leaf surfaces and in the leaf apoplast of its host, bean (Phaseolus vulgaris). To understand the contribution of distinct regulators to B728a fitness and pathogenicity, we performed a transcriptome analysis of strain B728a and nine regulatory mutants recovered from the surfaces and interior of leaves and exposed to environmental stresses in culture. The quorum-sensing regulators AhlR and AefR influenced few genes in planta or in vitro. In contrast, GacS and a downstream regulator, SalA, formed a large regulatory network that included a branch that regulated diverse traits and was independent of plant-specific environmental signals and a plant signal-dependent branch that positively regulated secondary metabolite genes and negatively regulated the type III secretion system. SalA functioned as a central regulator of iron status based on its reciprocal regulation of pyoverdine and achromobactin genes and also sulfur uptake, suggesting a role in the iron-sulfur balance. RetS functioned almost exclusively to repress secondary metabolite genes when the cells were not on leaves. Among the sigma factors examined, AlgU influenced many more genes than RpoS, and most AlgU-regulated genes depended on RpoN. RpoN differentially impacted many AlgU- and GacS-activated genes in cells recovered from apoplastic versus epiphytic sites, suggesting differences in environmental signals or bacterial stress status in these two habitats. Collectively, our findings illustrate a central role for GacS, SalA, RpoN, and AlgU in global regulation in B728a in planta and a high level of plasticity in these regulators’ responses to distinct environmental signals

Transcriptional responses of Pseudomonas syringae to growth in epiphytic versus apoplastic leaf sites

Some strains of the foliar pathogen Pseudomonas syringae are adapted for growth and survival on leaf surfaces and in the leaf interior. Global transcriptome profiling was used to evaluate if these two habitats offer distinct environments for bacteria and thus present distinct driving forces for adaptation. The transcript profiles of Pseudomonas syringae pv. syringae B728a support a model in which leaf surface, or epiphytic, sites specifically favor flagellar motility, swarming motility based on 3-(3-hydroxyalkanoyloxy)alkanoic acid surfactant production, chemosensing, and chemotaxis, indicating active relocation primarily on the leaf surface. Epiphytic sites also promote high transcript levels for phenylalanine degradation, which may help counteract phenylpropanoid-based defenses before leaf entry. In contrast, intercellular, or apoplastic, sites favor the high-level expression of genes for GABA metabolism (degradation of these genes would attenuate GABA repression of virulence) and the synthesis of phytotoxins, two additional secondary metabolites, and syringolin A. These findings support roles for these compounds in virulence, including a role for syringolin A in suppressing defense responses beyond stomatal closure. A comparison of the transcriptomes from in planta cells and from cells exposed to osmotic stress, oxidative stress, and iron and nitrogen limitation indicated that water availability, in particular, was limited in both leaf habitats but was more severely limited in the apoplast than on the leaf surface under the conditions tested. These findings contribute to a coherent model of the adaptations of this widespread bacterial phytopathogen to distinct habitats within its host

Characterization of multiple regulatory networks and responses to environmental signals in Pseudomonas syringae during its association with plants

Pseudomonas syringae is a model bacterial plant pathogen that is adapted for growth and survival on leaf surfaces and in the leaf interior of its host plants. P. syringae likely experiences distinct environmental conditions in different phases of its interaction with plants. In this study, we used global transcriptome profiling of P. syringae pv. syringae B728a to analyze genes and traits that were responsive to growth and survival on the leaf surface versus in the leaf apoplast. We found that the epiphytic environment specifically favors active relocation via flagellar motility, swarming motility, chemosensing, and chemotaxis, whereas the apoplastic environment favors traits contributing to virulence including the synthesis of two phytotoxins and syingolin A as well as the degradation of an alternative amino acid that suppresses virulence. Through comparing the transcriptomes of in planta cells to those of cells exposed to various stresses in culture media, we found that water limitation is a major stress that limits B728a growth and survival in these leaf habitats. P. syringae can adapt to water stress by the production of a potent compatible solute, trehalose. Distinct P. syringae strains vary in their ability to tolerate water stress, possibly due, in part, to differences in the production or regulation of trehalose. To investigate this possibility, we compared the relative contribution of the trehalose biosynthetic pathways to trehalose synthesis in two closely related P. syringae strains B728a and DC3000 and characterized an apparent interdependency between these pathways. Our data showed that, of the two trehalose biosynthesis pathways, only one was required for trehalose production in B728a whereas both were needed in DC3000, and moreover that differences in trehalose production may help explain differences in their water stress tolerance. Lastly, to understand the contribution of distinct regulators to fitness and pathogenicity of P. syringae, we performed a transcriptome analysis of B728a and mutants lacking each of nine regulators, including quorum-sensing regulators (AhlR and AefR), global regulators (GacS, SalA and RetS), and alternative sigma factors (RpoN, AlgU, RpoS, and HrpL), with cells recovered from the surface and interior of bean leaves as well as exposed to various environmental stresses. Our data showed that AhlR and AefR had negligible roles during B728a leaf colonization, whereas GacS and SalA had major roles. GacS/SalA formed a large regulatory network with both plant signal-dependent and plant signal-independent branches. RetS functioned almost exclusively to repress secondary metabolite genes when B728a cells were not in the leaf environment. Among the alternative sigma factors, RpoN influenced the majority of the genome whereas AlgU influenced a large number and RpoS a small number of genes, with plant signals strongly attenuating RpoN activation of the AlgU-regulated genes. Lastly, HrpL influenced very few genes in planta, due primarily to suppression by GacS and SalA. Collectively, our results highlight the role of these regulators during P. syringae colonization of leaves and the central importance of signals in the leaf environment on their regulation.</p

UV curing of a new epoxy formulation - kinetics multifunctional epoxy / cyclo epoxy adipate

UV curing has win a lot of attention nowadays and also seen a lot of application in fields like coatings, inks, adhesives and electronics. It is simple, fast and environment friendly and helps save cost & time in industry. UV curing making use of cationic polymerization is even better for it can be carried out in air. So a lot of research are looking into this field and many photoreactive formulations are being investigated to check their UV curing behavior. This project studies the formulation of Epiclon HP-7200, a new high performance type epoxy resin from DIC Corporation, as the monomer, Bis-(3, 4-epoxycyclohexyl) adipate as the co-solvent and Cyracure ® UVI-6976 as the photoinitiator using the photocalorimetry (DPC). Results show that this formulation system can function well in the sense that it can be UV cured and shows a consistency of the rate constant and activation energy & collision factor. Also, the proven applicability of the two modes for the autocatalyzed analysis lays foundation for future study. The effect of the UV light intensity which will increase the reaction rate is also proven. Finally, some recommendations are given to suggest some aspects that can be further investigated, including to exam the effects of other factors, and look into the electron beam curing of this formulation.Bachelor of Engineering (Materials Engineering

Curr. Nanosci.

In this work, magnetic Ni-cysteine hollow spheres were firstly fabricated by a facile room temperature self-assembly method. The most outstanding advantage of these hollow spheres is that the biocompatibility of amino acid and the magnetic property of metal nickel ions are successfully combined. Their coercivity in the magnetic measurement is 90 Oe at 80 K. This ferromagnetic performance and the satisfying blood compatibility in the anticoagulation test make them show promising applications in biological technique, especially the targeted drug delivery.In this work, magnetic Ni-cysteine hollow spheres were firstly fabricated by a facile room temperature self-assembly method. The most outstanding advantage of these hollow spheres is that the biocompatibility of amino acid and the magnetic property of metal nickel ions are successfully combined. Their coercivity in the magnetic measurement is 90 Oe at 80 K. This ferromagnetic performance and the satisfying blood compatibility in the anticoagulation test make them show promising applications in biological technique, especially the targeted drug delivery