菜籽饼肥对香蕉枯萎病的防效及其对土壤细菌的影响

研究菜籽饼肥对香蕉枯萎病的防治效果,探究菜籽饼肥施用后对土壤细菌群落的影响.设置2组实验,CN组为菜籽饼肥处理组,YN组为对照实验组.种植120d后,统计各组的发病率;利用qPCR技术检测2组中的FOC4孢子数量;采集2组土壤,利用Illumina Miseq高通量测序平台对CN处理组与YN对照组的土壤细菌群落结构和差异进行分析对比.实验研究发现:(1)施菜籽饼肥的CN处理组枯萎病发病率比YN对照组低63.33％;施用菜籽饼肥的处理土壤中FOC4的数量由2.94×104个/克土下降为1.96×103个/克土,YN对照组土壤中FOC4孢子的数量由2.94×104个/克土上升为4.55×105个/克土,CN处理组较YN对照组枯萎病菌数量下降了 2个数量级;(2)土壤细菌宏基因组微生物分类测序结果显示,CN处理组的Alpha多样性指数均优于YN对照组,这表明施用菜籽饼肥后增加了土壤细菌群落的丰度及多样性;(3)在门水平上,菜籽饼肥处理增加了变形菌门(Proteobacteria)和拟杆菌门(Bacteroidetes)的相对丰度,同时也降低了酸杆菌门(Acidobact-eria)、厚壁菌门(Firmicutes)和Patescibacteria等菌门的相对丰度;在属水平,CN处理组中的不动杆菌属(Aci-netobacter)、水杆菌属(Aquabacterium)、热单胞菌属(Thermomonas)、产黄杆菌属(Rhodanobacter)、假单胞菌属(Pseudomonas)和奥托氏菌属(Ottowia)等菌属的相对丰度较YN对照组有明显提高,而酸热菌属(Acidother-mus)、Bryobacter菌属以及Acidipila等菌属相对丰度较YN对照组有所减少.施用菜籽饼肥可以改变土壤中细菌的群落结构,显著降低土壤中FOC4孢子数量,从而降低香蕉枯萎病的发病率.本研究结果为菜籽饼肥用于香蕉枯萎病综合防控提供了理论依据.     

Profiling of Substrate Specificity of SARS-CoV 3CLpro

Background

The 3C-like protease (3CL^pro) of severe acute respiratory syndrome-coronavirus is required for autoprocessing of the polyprotein, and is a potential target for treating coronaviral infection.

Methodology/Principal Findings

To obtain a thorough understanding of substrate specificity of the protease, a substrate library of 198 variants was created by performing saturation mutagenesis on the autocleavage sequence at P5 to P3'' positions. The substrate sequences were inserted between cyan and yellow fluorescent proteins so that the cleavage rates were monitored by in vitro fluorescence resonance energy transfer. The relative cleavage rate for different substrate sequences was correlated with various structural properties. P5 and P3 positions prefer residues with high β-sheet propensity; P4 prefers small hydrophobic residues; P2 prefers hydrophobic residues without β-branch. Gln is the best residue at P1 position, but observable cleavage can be detected with His and Met substitutions. P1'' position prefers small residues, while P2'' and P3'' positions have no strong preference on residue substitutions. Noteworthy, solvent exposed sites such as P5, P3 and P3'' positions favour positively charged residues over negatively charged one, suggesting that electrostatic interactions may play a role in catalysis. A super-active substrate, which combined the preferred residues at P5 to P1 positions, was found to have 2.8 fold higher activity than the wild-type sequence.

Conclusions/Significance

Our results demonstrated a strong structure-activity relationship between the 3CL^pro and its substrate. The substrate specificity profiled in this study may provide insights into a rational design of peptidomimetic inhibitors.     

Protective effects of pre-germinated brown rice diet on low levels of Pb-induced learning and memory deficits in developing rat

Lead (Pb) is a known neurotoxicant in humans and experimental animals. Numerous studies have provided evidence that humans, especially young children, and animals chronically intoxicated with low levels of Pb show learning and memory impairments. Unfortunately, Pb-poisoning cases continue to occur in many countries. Because the current treatment options are very limited, there is a need for alternative methods to attenuate Pb toxicity. In this study, the weaning (postnatal day 21, PND21) rats were randomly divided into five groups: the control group (AIN-93G diet, de-ionized water), the lead acetate (PbAC) group (AIN-93G diet, 2 g/L PbAC in de-ionized water), the lead acetate + WR group (white rice diet, 2 g/L PbAC in de-ionized water; PbAC + WR), the lead acetate + BR group (brown rice diet, 2 g/L PbAC in de-ionized water; PbAC + BR) and the lead acetate + PR group (pre-germinated brown rice diet, 2 g/L PbAC in de-ionized water; PbAC + PR). The animals received the different diets until PND60, and then the experiments were terminated. The protective effects of pre-germinated brown rice (PR) on Pb-induced learning and memory impairment in weaning rats were assessed by the Morris water maze and one-trial-learning passive avoidance test. The anti-oxidative effects of feeding a PR diet to Pb-exposed rats were evaluated. The levels of reactive oxygen species (ROS) were determined by flow cytometry. The levels of 8-hydroxy-2-deoxyguanosine (8-OHdG), γ-aminobutyric acid (GABA) and glutamate were determined by HPLC. Our data showed that feeding a PR diet decreased the accumulation of lead and decreased Pb-induced learning and memory deficits in developing rats. The mechanisms might be related to the anti-oxidative effects and large amount of GABA in PR. Our study provides a regimen to reduce Pb-induced toxicity, especially future learning and memory deficits in the developing brain.     

"In vitro" protection of DNA from Fenton reaction by plant polyphenol verbascoside

The protection effect of verbascoside (Ver) against Fenton reaction on plasmid pBR322 DNA was studied using agarose gel electrophoresis and UV-visible spectroscopy. The pBR322 plasmid DNA is damaged by hydroxyl radical (OH*) generated from the Fenton reaction with H2O2 and Fe(II) or Fe(III). This DNA damage is characterized by the diminution of supercoiled DNA forms or by the increase of relaxed or linear DNA forms after oxidative attack. The UV spectrum study showed that verbascoside can form complexes with Fe(II) or Fe(III), and the complexation can be reversed by the addition of EDTA. The formation constants of verbascoside-Fe complexes were estimated as 10(21.03) and 10(31.94) M(-2) for Fe(II) and Fe(III) respectively. The inhibition of Fenton reaction by verbascoside could be partially explained by the sequestration of Fe ions.     

A truncated Fibrobacter succinogenes 1,3-1,4-beta-d-glucanase with improved enzymatic activity and thermotolerance

As an approach to improving Fibrobacter succinogenes 1,3-1,4-beta-d-glucanase (Fsbeta-glucanase) for use in industry and to studying the structure-function relationship of the C-terminus in the enzyme, a C-terminally truncated ( approximately 10 kDa) Fsbeta-glucanase was generated using a PCR-based gene truncation method and then overexpressed in either Escherichia coli BL21(DE3) or Pichia pastoris strain X-33 host cells. The initial rate kinetics, protein folding, and thermostability of the wild-type and truncated glucanases were characterized. The truncated enzyme expressed in Pichia cells was found to be glycosylated and composed of two dominant polypeptide bands as judged by SDS-PAGE. An approximate 3-4-fold increase in the turnover rate (k(cat)), relative to that of the full-length enzyme, was detected for the purified truncated glucanases produced in E. coli (designated TF-glucanase) or Pichia host cells (designated glycosylated TF-glucanase). The glycosylated TF-glucanase is the most active known 1,3-1,4-beta-d-glucanase, with a specific activity of 10 800 +/- 200 units/mg. Similar binding affinities for lichenan (K(m) = 2.5-2.89 mg/mL) were detected for the full-length enzyme, TF-glucanase, and glycosylated TF-glucanase. Both forms of truncated glucanase retained more than 80% of their original enzymatic activity after a 10 min incubation at 90 degrees C, whereas the full-length enzyme possessed only 30% of its original enzymatic activity after the same treatment. This report demonstrates that deletion of the C-terminal region ( approximately 10 kDa) in Fsbeta-glucanase, consisting of serine-rich repeats and a basic terminal domain rich in positively charged amino acids, significantly increases the catalytic efficiency and thermotolerance of the enzyme.     

RACK1 binds to a signal transfer region of G betagamma and inhibits phospholipase C beta2 activation

Receptor for Activated C Kinase 1 (RACK1), a novel G betagamma-interacting protein, selectively inhibits the activation of a subclass of G betagamma effectors such as phospholipase C beta2 (PLCbeta2) and adenylyl cyclase II by direct binding to G betagamma (Chen, S., Dell, E. J., Lin, F., Sai, J., and Hamm, H. E. (2004) J. Biol. Chem. 279, 17861-17868). Here we have mapped the RACK1 binding sites on G betagamma. We found that RACK1 interacts with several different G betagamma isoforms, including G beta1gamma1, Gbeta1gamma2, and Gbeta5gamma2, with similar affinities, suggesting that the conserved residues between G beta1 and G beta5 may be involved in their binding to RACK1. We have confirmed this hypothesis and shown that several synthetic peptides corresponding to the conserved residues can inhibit the RACK1/G betagamma interaction as monitored by fluorescence spectroscopy. Interestingly, these peptides are located at one side of G beta1 and have little overlap with the G alpha subunit binding interface. Additional experiments indicate that the G betagamma contact residues for RACK1, in particular the positively charged amino acids within residues 44-54 of G beta1, are also involved in the interaction with PLCbeta2 and play a critical role in G betagamma-mediated PLCbeta2 activation. These data thus demonstrate that RACK1 can regulate the activity of a G betagamma effector by competing for its binding to the signal transfer region of G betagamma.     

Lifespan and patterns of accumulation and mobilization of nutrients in the sugar-fed phorid fly, Pseudacteon tricuspis

Abstract. The effect of sugar feeding on the survival of adult phorid fly Pseudacteon tricuspis is investigated. Flies fed 25% sucrose in aqueous solution continuously throughout their lifespan have greater longevity (mean ± SE longevity: female = 7.9 ± 0.8 days, male = 8.9 ± 0.9 days) than completely starved (provided no water and no sugar solution) flies, sugar-starved (provided water only) flies, or flies fed sugar solution only on their first day of adult life. Completely starved flies rarely lived beyond one day. Provision of water increases longevity by 2 days, and one full day of sugar feeding further increases longevity by an additional 1–2 days. Flies fed 50% sucrose have similar survivorship as those fed 25% sucrose. The temporal patterns of nutrient accumulation and utilization are also compared in P. tricuspis fed different diets: sugar-starved, sucrose-fed on the first day of adult life only, and sucrose-fed continuously. Adult P. tricuspis emerge with no gut sugars, and only minimal amounts of body sugars and glycogen. Although the levels of body sugars and glycogen decline gradually in sugar-starved flies, a single day of sugar feeding results in the accumulation of maximum amounts of gut sugars, body sugars and glycogen. High levels of these nutrients are maintained in female and male phorid flies fed on sucrose continuously over the observation period, whereas nutrient levels decline in flies fed only on the first day of life, beginning 1 day postfeeding. Female and male P. tricuspis emerge with an estimated 12.3 ± 2.3 and 7.2 ± 1 g of lipid reserves per fly, respectively. These teneral amounts represent the highest lipid levels detected in adult flies, irrespective of their diet, and are maintained over the life times of sucrose-fed female and male flies, but declined steadily in sugar-starved females. These data suggest that adult P. tricuspis are capable of converting dietary sucrose to body sugars and glycogen, but not lipids.     

黏附分子在肿瘤发生及发展中的作用

细胞黏附分子是以配体和受体相结合的形式,介导细胞与细胞间或细胞与基质间相互作用的一类分子,参与机体的多种重要生理和病理过程.近年来,在对肿瘤发生和发展的研究中发现,黏附分子可通过多种途径影响肿瘤的生长、浸润及转移过程.因此.对黏附分子在肿瘤发生和发展中作用及机制的深入研究,可为肿瘤早期诊断提供重要的分子指标和发现新的治疗靶标.并为进而形成临床诊疗新策略提供重要理论支持.现就几种重要黏附分子在肿瘤生长与转移中的作用进行综述.     

Microbial subversion of heparan sulfate proteoglycans

The interactions between the host and microbial pathogen largely dictate the onset, progression, and outcome of infectious diseases. Pathogens subvert host components to promote their pathogenesis and, among these, cell surface heparan sulfate proteoglycans are exploited by many pathogens for their initial attachment and subsequent cellular entry. The ability to interact with heparan sulfate proteoglycans is widespread among viruses, bacteria, and parasites. Certain pathogens also use heparan sulfate proteoglycans to evade host defense mechanisms. These findings suggest that heparan sulfate proteoglycans are critical in microbial pathogenesis, and that heparan sulfate proteoglycan-pathogen interactions are potential targets for novel prophylactic and therapeutic approaches.