Differential effectiveness of Serratia plymuthica IC1270-induced systemic resistance against hemibiotrophic and necrotrophic leaf pathogens in rice

Background  

Induced resistance is a state of enhanced defensive capacity developed by a plant reacting to specific biotic or chemical stimuli. Over the years, several forms of induced resistance have been characterized, including systemic acquired resistance, which is induced upon localized infection by an avirulent necrotizing pathogen, and induced systemic resistance (ISR), which is elicited by selected strains of nonpathogenic rhizobacteria. However, contrary to the relative wealth of information on inducible defense responses in dicotyledoneous plants, our understanding of the molecular mechanisms underlying induced resistance phenomena in cereal crops is still in its infancy. Using a combined cytomolecular and pharmacological approach, we analyzed the host defense mechanisms associated with the establishment of ISR in rice by the rhizobacterium Serratia plymuthica IC1270.     

DNABII proteins play a central role in UPEC biofilm structure

Most chronic and recurrent bacterial infections involve a biofilm component, the foundation of which is the extracellular polymeric substance (EPS). Extracellular DNA (eDNA) is a conserved and key component of the EPS of pathogenic biofilms. The DNABII protein family includes integration host factor (IHF) and histone‐like protein (HU); both are present in the extracellular milieu. We have shown previously that the DNABII proteins are often found in association with eDNA and are critical for the structural integrity of bacterial communities that utilize eDNA as a matrix component. Here, we demonstrate that uropathogenic Escherichia coli (UPEC) strain UTI89 incorporates eDNA within its biofilm matrix and that the DNABII proteins are not only important for biofilm growth, but are limiting; exogenous addition of these proteins promotes biofilm formation that is dependent on eDNA. In addition, we show that both subunits of IHF, yet only one subunit of HU (HupB), are critical for UPEC biofilm development. We discuss the roles of these proteins in context of the UPEC EPS.     

p24 proteins play a role in peroxisome proliferation in yeast

Emp24 is a member of the p24 protein family, which was initially localized to the endoplasmic reticulum, Golgi and COP vesicles, but has recently shown to be associated with Saccharomyces cerevisiae peroxisomes as well. Using cell fractionation and electron- and fluorescence microscopy, we show that in the yeast Hansenula polymorpha, Emp24 also associates with peroxisomes. In addition, we show that peroxisome numbers are strongly decreased in H. polymorpha cells lacking two proteins of the p24 complex, Emp24 and Erp3. Detailed fluorescence microscopy analyses suggest that emp24.erp3 cells are disturbed in peroxisome fission and inheritance.     

Insights into the role of jasmonic acid-mediated defenses against necrotrophic and biotrophic fungal pathogens

Jasmonic acid (JA) is a natural hormone regulator involved in development,responses against wounding and pathogen attack.Upon perception of pathogens,JA is synthesized and mediates a signaling cascade ...     

SNARE proteins play a role in motor axon guidance in vertebrates and invertebrates

Axonal growth and guidance rely on correct growth cone responses to guidance cues, both in the central nervous system (CNS) and in the periphery. Unlike the signaling cascades that link axonal growth to cytoskeletal dynamics, little is known about the cross‐talk mechanisms between guidance and membrane dynamics and turnover in the axon. Our studies have shown that Netrin‐1/deleted in colorectal cancer signaling triggers exocytosis through the SNARE Syntaxin‐1 (STX‐1) during the formation of commissural pathways. However, limited in vivo evidence is available about the role of SNARE proteins in motor axonal guidance. Here we show that loss‐of‐function of SNARE complex members results in motor axon guidance defects in fly and chick embryos. Knock‐down of Syntaxin‐1, VAMP‐2, and SNAP‐25 leads to abnormalities in the motor axon routes out of the CNS. Our data point to an evolutionarily conserved role of the SNARE complex proteins in motor axon guidance, thereby pinpointing an important function of SNARE proteins in axonal navigation in vivo . © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 963–974, 2017     

Natural resistance mechanisms may play a role in protection against chemical carcinogenesis

Summary Mice deprived of B lymphocytes by the chronic administration of anti-IgM antibodies have been shown to possess a heightened natural resistance (NR) to micro-organisms, to parental bone marrow, and to natural killer (NK)-sensitive tumors in vitro and in vivo. Experiments described in this communication indicate that the latent period of primary tumors induced by the injection of methylcholanthrene (MC) is also prolonged in these mice. This observation suggests that NR mechanisms may provide protection against primary chemically induced tumors. Abbreviations used in this paper: MC, methylcholanthrene; NR, natural resistance; NRG, normal rabbit serum pool; NK, natural killer cell     

钾离子通道蛋白Shaker对果蝇心脏衰老的保护作用

钾离子通道在心肌细胞动作电位复极过程中起着重要作用。钾离子通道蛋白种类繁多,已知钾离子通道蛋白KCNQ和HERG/eag参与心脏动作电位的形成,调节心脏收缩节律。钾离子通道蛋白Shaker是果蝇(Drosophila)体内发现的第一个电压门控钾离子通道,维持神经元和肌肉细胞的电兴奋性,但是目前其在成人心脏功能中的作用仍不清楚。本研究以果蝇为模型,高频电刺激模拟心脏应激状态,观察钾离子通道蛋白shaker基因突变体的心衰发生率。同时,利用心脏特异性启动子hand4.2Gal4特异性敲低钾离子通道蛋白Shaker的表达;果蝇成体心脏生理学功能分析系统分析了1、3、5周龄特异性敲低钾离子通道蛋白Shaker的心脏表型。结果表明,shaker基因突变将严重影响果蝇心脏抗应激能力,表现在高频电刺激后的心力衰竭发生率显著性升高;心脏特异性敲低shaker基因导致5周龄果蝇心律失常发生率显著性增加;心脏特异性敲低HDAC3将显著降低果蝇寿命。综上所述,本研究推测钾离子通道蛋白Shaker在衰老过程中维护果蝇正常的心脏功能。     

Peroxiredoxins play a major role in protecting Trypanosoma cruzi against macrophage- and endogenously-derived peroxynitrite

There is increasing evidence that Trypanosoma cruzi antioxidant enzymes play a key immune evasion role by protecting the parasite against macrophage-derived reactive oxygen and nitrogen species. Using T. cruzi transformed to overexpress the peroxiredoxins TcCPX (T. cruzi cytosolic tryparedoxin peroxidase) and TcMPX (T. cruzi mitochondrial tryparedoxin peroxidase), we found that both cell lines readily detoxify cytotoxic and diffusible reactive oxygen and nitrogen species generated in vitro or released by activated macrophages. Parasites transformed to overexpress TcAPX (T. cruzi ascorbate-dependent haemoperoxidase) were also more resistant to H2O2 challenge, but unlike TcMPX and TcCPX overexpressing lines, the TcAPX overexpressing parasites were not resistant to peroxynitrite. Whereas isolated tryparedoxin peroxidases react rapidly (k=7.2 x 10(5) M(-1) x s(-1)) and reduce peroxynitrite to nitrite, our results demonstrate that both TcMPX and TcCPX peroxiredoxins also efficiently decompose exogenous- and endogenously-generated peroxynitrite in intact cells. The degree of protection provided by TcCPX against peroxynitrite challenge results in higher parasite proliferation rates, and is demonstrated by inhibition of intracellular redox-sensitive fluorescence probe oxidation, protein 3-nitrotyrosine and protein-DMPO (5,5-dimethylpyrroline-N-oxide) adduct formation. Additionally, peroxynitrite-mediated over-oxidation of the peroxidatic cysteine residue of peroxiredoxins was greatly decreased in TcCPX overexpressing cells. The protective effects generated by TcCPX and TcMPX after oxidant challenge were lost by mutation of the peroxidatic cysteine residue in both enzymes. We also observed that there is less peroxynitrite-dependent 3-nitrotyrosine formation in infective metacyclic trypomastigotes than in non-infective epimastigotes. Together with recent reports of up-regulation of antioxidant enzymes during metacyclogenesis, our results identify components of the antioxidant enzyme network of T. cruzi as virulence factors of emerging importance.     

Defensins play a crucial role in protecting mice against oral Shigella flexneri infection

An earlier study revealed that 4-day-old mice, but not older mice, were infected with invasive Shigella strains. Here we attempted to determine the underlying mechanism that induces inflammation in the intestines of neonate mice after oral Shigella infection. Wild-type BALB/c mice of different ages (7, 14, and 35 days old) were orally administered GFP-expressing Shigella flexneri 5a M90T strain (5 × 10⁹ CFU) and analyzed for colonization 6 h following infection. We found that Shigella localized in the epithelium, lamina propria, and crypt regions of the small intestines of 7-day-old BALB/c mice. Microarray analysis revealed that expression levels of cryptdin and various types of cryptdin-related mRNA (e.g., cryptrs-2, -5, -7, -12 and lysozyme) in the small intestines were significantly lower in 7-day-old than in older mice regardless of Shigella infection status. Interestingly, matrix metalloprotease-7 (matrilysin)-deficient (MAT^−/−) mice of B6 background had more colonies and more severe symptoms of inflammation in the intestines than did wild-type B6 mice after oral Shigella challenge. This suggests that cryptdin-related antimicrobial molecules are indispensable for efficient protection against oral Shigella infection.     

Electrostatic and hydrophobic interactions play a major role in the stability and refolding of halophilic proteins

In general, halophilic proteins are stable only in the presence of salts at high concentrations. Not only is high salt concentration important for structural stability of halophilic proteins, but also refolding of a denatured halophilic protein requires high salt concentration. This review summarizes the importance of electrostatic charge shielding and hydrophobic interactions in the stability and refolding of halophilic proteins.     

Marine microorganisms as biocontrol agents against fungal phytopathogens and mycotoxins

Mycotoxins are a serious food safety concern for human and animal health. Much attention should be paid to the dietary exposure to mycotoxins in order to minimise the risk of mycotoxin contamination in the food chain. Among the reported strategies to manage the mycotoxin contamination into food and feed, biological control seems a promising approach, depending on their biological origins, and on the use of living organisms or their derivatives. Marine microorganisms have developed unique metabolic and physiological capabilities to thrive in extreme habitats and produce novel metabolites which are not often present in microbes of terrestrial origin. Some marine bacteria and fungi have a good potential for the control of fungal phytopathogens and mycotoxins. Biologists and chemists are needed to work together to explore the storehouse of marine microorganisms and marine active metabolites, because marine bacteria and fungi have a huge potential for practical application in biocontrol of fungal phytopathogens and preventing mycotoxin contamination.     

The role of effectors of biotrophic and hemibiotrophic fungi in infection

Biotrophic and hemibiotrophic fungi are successful groups of plant pathogens that require living plant tissue to survive and complete their life cycle. Members of these groups include the rust fungi and powdery mildews and species in the Ustilago, Cladosporium and Magnaporthe genera. Collectively, they represent some of the most destructive plant parasites, causing huge economic losses and threatening global food security. During plant infection, pathogens synthesize and secrete effector proteins, some of which are translocated into the plant cytosol where they can alter the host's response to the invading pathogen. In a successful infection, pathogen effectors facilitate suppression of the plant's immune system and orchestrate the reprogramming of the infected tissue so that it becomes a source of nutrients that are required by the pathogen to support its growth and development. This review summarizes our current understanding of the function of fungal effectors in infection.     

Solubility-enhancing proteins MBP and NusA play a passive role in the folding of their fusion partners

It is well established that certain highly soluble proteins have the ability to enhance the solubility of their fusion partners. However, very little is known about how different solubility enhancers compare in terms of their ability to promote the proper folding of their passenger proteins. We compared the ability of two well-known solubility enhancers, Escherichia coli maltose-binding protein (MBP) and N utilization substance A (NusA), to improve the solubility and promote the proper folding of a variety of passenger proteins that are difficult to solubilize. We used an intracellular processing system to monitor the solubility of these passenger proteins after they were cleaved from MBP and NusA by tobacco etch virus protease. In addition, the biological activity of some fusion proteins was compared to serve as a more quantitative indicator of native structure. The results indicate that MBP and NusA have comparable solubility-enhancing properties. Little or no difference was observed either in the solubility of passenger proteins after intracellular processing of the MBP and NusA fusion proteins or in the biological activity of solubilized passenger proteins, suggesting that the underlying mechanism of solubility enhancement is likely to be similar for both the proteins, and that they play a passive role rather than an active one in the folding of their fusion partners.     

Secretory avocado idioblast oil cells: evidence of their defensive role against a non-adapted insect herbivore

We tested the hypothesis that avocado idioblast oil cells play a defensive role against herbivorous insects. Toxicities of the intact avocado idioblast oil cells and the extracted idioblast oil were compared for three insect herbivores. Spodoptera exigua (Hübner) larvae are generalists that do not feed on avocados. By contrast, Sabulodes aegrotata (Guenée) and Pseudoplusia includens (Walker) larvae are generalist herbivores that readily feed on avocados. All bioassays were performed at a naturally occurring concentration of idioblast oil cells (2% w/w). Choice experiments showed that S. exigua larvae avoided diet treated with avocado idioblast oil cells and consume more control than treated diet. In contrast, idioblast oil cells had no significant antifeedant effects on the adapted S. aegrotata and P. includens larvae. Subsequent experiments designed to assess resistance mechanisms separated pre-ingestive (behavioral) and post-ingestive (physiological) effects of the avocado idioblast oil cells, and the extracted idioblast oil, on the two adapted herbivores. Post-ingestive adaptation was the mechanism that allows feeding. Because the impact of the avocado idioblast oil cells was greatest on the performance of non-adapted S. exigua, additional experiments determined that larvae fed diet containing the oil cells had higher mortality and reduced larval growth compared to controls. Developmental times were significantly prolonged for the survivors. Thus, increased mortality, reduced developmental rates, and antifeedant activity in the non-adapted insect indicate that defense against non-adapted herbivores may be an important function of idioblast cells in avocados.     

RNAi: a defensive RNA-silencing against viruses and transposable elements

RNA silencing is a form of nucleic-acid-based immunity, targeting viruses and genomic repeated sequences. First documented in plants and invertebrate animals, this host defence has recently been identified in mammals. RNAi is viewed as a conserved ancient mechanism protecting genomes from nucleic acid invaders. However, these tamed sequences are known to occasionally escape this host surveillance and invade the genome of their host. This response is consistent with the overall idea that parasitic sequences compete with cells to systematically counter host defences. Using examples taken from the current literature, we illustrate the dynamic move-countermove game played between these two protagonists, the host cell and its parasitic sequences, and discuss the consequences of this game on genome stability.     

Electrostatic interactions play a critical role in Mycobacterium tuberculosis Hsp16.3 binding of substrate proteins

Mycobacterium tuberculosis Hsp16.3, a member of a small heat shock protein family, has chaperone-like activity in vitro and suppresses thermally or chemically induced aggregation of proteins. The nature of the interactions between Hsp16.3 and the denatured substrate proteins was investigated. A dramatic enhancement of chaperone-like activity of Hsp16.3 upon increasing temperature was accompanied by decreased ANS-detectable surface hydrophobicity. Hsp16.3 exhibited significantly enhanced chaperone-like activity after preincubation at 100°C with almost unchanged surface hydrophobicity. The interaction between Hsp16.3 and dithiothreitol-treated insulin B chains was markedly weakened in the presence of NaCl but greatly enhanced by the addition of a low-polarity alcohol, accompanied by significantly increased and decreased surface hydrophobicity, respectively. A working model for Hsp16.3 binding to its substrate proteins is proposed.     

Rhizobium NodI and NodJ proteins play a role in the efficiency of secretion of lipochitin oligosaccharides.

Thin-layer chromatographic analysis of extracts of D-[1-14C]glucosamine-labelled rhizobia was used to analyze the effects of nodI, nodJ, and nodT on secretion of lipochitin oligosaccharide (LCO) signal molecules. Secretion was analyzed by comparing quantities of radiolabelled LCOs present in the cellular and spent growth medium fractions. A second rapid and sensitive method was introduced to estimate the secreted LCO fractions by using D-[1-14C]glucosamine-labelled cells grown in medium supplemented with chitinase. At various times after induction of LCO synthesis, the quantity of degradation products of LCOs was compared with the amount of nondegraded LCOs. In wild-type strains of Rhizobium leguminosarum biovars viciae and trifolii the nodI and nodJ genes (but not the nodT gene) strongly enhance the secretion of LCOs during the first 5 h after the induction of LCO synthesis. In LCO-overproducing strains the enhancement of secretion was observed only during the first 3 h after induction. At times later than 5 h after induction, a significant influence of the presence of the nodI and nodJ genes on LCO secretion was detectable neither in the wild type nor in LCO-overproducing strains. By using plasmids in which the nodI and nodJ genes are cloned separately under control of a flavonoid-inducible promoter, it was shown that both genes are needed for a wild-type level of LCO secretion. Therefore, these results demonstrate that nodI and nodJ play a role in determining the efficiency of LCO secretion.