Priming Of Defense Responses Research Articles

γ-Aminobutyric acid induces resistance against Penicillium expansum by priming of defence responses in pear fruit

The results from this study showed that treatment with γ-aminobutyric acid (GABA), at 100–1000μg/ml, induced strong resistance against blue mould rot caused by Penicillium expansum in pear fruit. Moreover, the activities of five defence-related enzymes (including chitinase, β-1,3-glucanase, phenylalnine ammonialyase, peroxidase and polyphenol oxidase) and the expression of these corresponding genes were markedly and/or promptly enhanced in the treatment with GABA and inoculation with P. expansum compared with those that were treated with GABA or inoculated with pathogen alone. In addition, the treatment of pear with GABA had little adverse effect on the edible quality of the fruit. To the best of our knowledge, this is the first report that GABA can effectively reduce fungal disease of harvested fruit. Its mechanisms may be closely correlated with the induction of fruit resistance by priming activation and expression of defence-related enzymes and genes upon challenge with pathogen.

Mitogen-activated Protein Kinase Signaling in Inflammation-related Carcinogenesis

The role of mitogen-activated protein kinases (MAPKs) in regulation of inflammation is well known. MAPK family is activated by various stimuli and involved in transmitting extracellular signals to nucleus leading to gene regulation. Inflammation is primary defensive response of host against microbes. Controlled inflammation is helpful and indispensable for host defense. However, uncontrolled inflammatory response leads to various inflammatory diseases and cancer. Persistent inflammation leads to cell proliferation and survival that plays crucial role in tumorigenesis. In this review, we recapitulate the recent knowledge of MAPK signaling and its roles in inflammation-associated carcinogenesis.

Involvement of phospholipase D and NADPH-oxidase in salicylic acid signaling cascade

Salicylic acid is associated with the primary defense responses to biotic stress and formation of systemic acquired resistance. However, molecular mechanisms of early cell reactions to phytohormone application are currently undisclosed. The present study investigates the participation of phospholipase D and NADPH-oxidase in salicylic acid signal transduction cascade. The activation of lipid signaling enzymes within 15 min of salicylic acid application was shown in Arabidopsis thaliana plants by measuring the phosphatidic acid accumulation. Adding of primary alcohol (1-butanol) to the incubation medium led to phosphatidylbutanol accumulation as a result of phospholipase D (PLD) action in wild-type and NADPH-oxidase RbohD deficient plants. Salicylic acid induced rapid increase in NADPH-oxidase activity in histochemical assay with nitroblue tetrazolium but the reaction was not observed in presence of 1-butanol and NADPH-oxidase inhibitor diphenylene iodide (DPI). The further physiological effect of salicylic acid and inhibitory analysis of the signaling cascade were made in the guard cell model. Stomatal closure induced by salicylic acid was inhibited by 1-butanol and DPI treatment. rbohD transgenic plants showed impaired stomatal reaction upon phytohormone effect, while the reaction to H2O2 did not differ from that of wild-type plants. Thus a key role of NADPH-oxidase D-isoform in the process of stomatal closure in response to salicylic acid has been postulated. It has enabled to predict a cascade implication of PLD and NADPH oxidase to salicylic acid signaling pathway.

Reactive Oxygen Species (ROS): Role in Plant Defense

Reactive oxygen species (ROS) play an important role in the defense response of plants against various pathogens and under stress conditions. Any stress condition results in the excess production of reactive oxygen species (ROS) e.g. superoxide, hydrogen peroxide and hydroxyl radicals, a phenomenon known as the oxidative burst, which is the primary defense response against pathogens in the early stages of infection. These ROS species, some of which are toxic are rapidly detoxified by various cellular enzymatic and non-enzymatic mechanisms. The present paper deals with the ROS, mechanism, chemistry and their role in the defense response of plants.

Bacillus cereus AR156 induces resistance against Rhizopus rot through priming of defense responses in peach fruit

The biocontrol effects of Bacillus cereus AR156 on Rhizopus rot caused by Rhizopus stolonifer in postharvest peach fruit and the possible mechanisms were investigated. The results showed that fruit treated with B. cereus AR156 had significantly lower disease incidence and smaller lesion diameter than the control fruit did. B. cereus AR156 treatment remarkably enhanced activities of chitinase and β-1,3-glucanase, promoted accumulation of H2O2, and improved total phenolic content and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity. Transcripts of four defense related genes were only significantly enhanced in fruit both treated with B. cereus AR156 and inoculated with R. stolonifer compared with those that were only treated with B. cereus AR156 or inoculated with R. stolonifer. These results suggest that B. cereus AR156 can effectively inhibit Rhizopus rot caused by R. stolonifer and enhance antioxidant activity in peach fruit through the priming of defense responses.

Thiamine induced resistance to Plasmopara viticola in grapevine and elicited host–defense responses, including HR like-cell death

Recently, thiamine (VitaminB1) has been shown to induce resistance against Pseudomonas syringae in Arabidopsis plants through priming of defense responses. In this paper, we have demonstrated the efficiency of thiamine to induce resistance against downy mildew caused by the oomycete Plasmopara viticola in a susceptible Vitis vinifera cultivar "Chardonnay" under glasshouse controlled conditions by providing a dual mode of action involving direct antifungal activity and elicitation of host-defense responses. Thiamine-induced defense responses included the generation of hydrogen peroxide (H(2)O(2)) in both grapevine suspension cultured cells (SCC) and plant leaves, upregulation of an array of defense-related genes and the induction of other defense responses at subcellular level such as callose deposition in stomata cells, phenolic compounds accumulation and hypersensitive response (HR) like-cell death. Epifluorescence microscopy studies revealed dramatic changes in P. viticola individual developmental stages during its colonization of the intercellular space of the leaf mesophyll in thiamine-treated plants. Collectively, our report evidenced the efficiency of thiamine in the control of downy mildew in grapevine by direct and indirect effects, suggesting that thiamine could be an attractive alternative to chemical fungicides in disease management in vineyards.

Aversive life events enhance human freezing responses.

In the present study, we investigated the effect of prior aversive life events on freezing-like responses. Fifty healthy females were presented neutral, pleasant, and unpleasant images from the International Affective Picture System while standing on a stabilometric platform and wearing a polar band to assess body sway and heart rate. In the total sample, only unpleasant pictures elicited reduced body sway and reduced heart rate (freezing). Moreover, participants who had experienced 1 or more aversive life events showed greater reductions in heart rate for unpleasant versus pleasant pictures than those who had experienced no such event. In addition, relative to no-event participants, single-event participants showed reduced body sway to unpleasant pictures, while multiple-event participants showed reduced body sway in response to all picture categories. These results indicate that aversive life events affect automatic freezing responses and may indicate the cumulative effect of multiple trauma. The experimental paradigm presented is a promising method to study freezing as a primary defense response in trauma-related disorders.

Cytokinins Mediate Resistance againstPseudomonas syringaein Tobacco through Increased Antimicrobial Phytoalexin Synthesis Independent of Salicylic Acid Signaling

Cytokinins are phytohormones that are involved in various regulatory processes throughout plant development, but they are also produced by pathogens and known to modulate plant immunity. A novel transgenic approach enabling autoregulated cytokinin synthesis in response to pathogen infection showed that cytokinins mediate enhanced resistance against the virulent hemibiotrophic pathogen Pseudomonas syringae pv tabaci. This was confirmed by two additional independent transgenic approaches to increase endogenous cytokinin production and by exogenous supply of adenine- and phenylurea-derived cytokinins. The cytokinin-mediated resistance strongly correlated with an increased level of bactericidal activities and up-regulated synthesis of the two major antimicrobial phytoalexins in tobacco (Nicotiana tabacum), scopoletin and capsidiol. The key role of these phytoalexins in the underlying mechanism was functionally proven by the finding that scopoletin and capsidiol substitute in planta for the cytokinin signal: phytoalexin pretreatment increased resistance against P. syringae. In contrast to a cytokinin defense mechanism in Arabidopsis (Arabidopsis thaliana) based on salicylic acid-dependent transcriptional control, the cytokinin-mediated resistance in tobacco is essentially independent from salicylic acid and differs in pathogen specificity. It is also independent of jasmonate levels, reactive oxygen species, and high sugar resistance. The novel function of cytokinins in the primary defense response of solanaceous plant species is rather mediated through a high phytoalexin-pathogen ratio in the early phase of infection, which efficiently restricts pathogen growth. The implications of this mechanism for the coevolution of host plants and cytokinin-producing pathogens and the practical application in agriculture are discussed.

Systemic acquired resistance is induced by R gene‐mediated responses independent of cell death

On infection by pathogens, plants initiate defence responses that are able to curtail infection locally. These responses are mediated either by receptor-like proteins that recognize pathogen-associated molecular patterns or by the protein products of disease resistance (R) genes. At the same time, primary defence responses often result in the generation of signals that induce what is known as systemic acquired resistance (SAR), such that defence responses are enhanced on secondary pathogen challenge in distal tissues. R protein-mediated SAR induction is normally accompanied by a type of programmed cell death known as the hypersensitive response (HR) and, in some instances, cell death alone has been implicated in the induction of SAR. This has raised the question of whether R protein-mediated signalling per se induces SAR or whether SAR is an indirect result of the induction of HR. Using the Rx gene of potato, which confers resistance to Potato Virus X in the absence of cell death, we have shown that the HR is dispensable for R protein-mediated induction of SAR and that Rx-induced SAR is mediated by the same salicylate-dependent pathway induced by other R proteins.

Pseudomonas spp.-induced systemic resistance to Botrytis cinerea is associated with induction and priming of defence responses in grapevine

Non-pathogenic rhizobacteria Pseudomonas spp. can reduce disease in plant tissues through induction of a defence state known as induced systemic resistance (ISR). This resistance is based on multiple bacterial determinants, but nothing is known about the mechanisms underlying rhizobacteria-induced resistance in grapevine. In this study, the ability of Pseudomonas fluorescens CHA0 and Pseudomonas aeruginosa 7NSK2 to induce resistance in grapevine against Botrytis cinerea is demonstrated. Both strains also triggered an oxidative burst and phytoalexin (i.e. resveratrol and viniferin) accumulation in grape cells and primed leaves for accelerated phytoalexin production upon challenge with B. cinerea. Treatment of cell cultures with crude cell extracts of bacteria strongly enhanced oxidative burst, but resulted in comparable amounts of phytoalexins and resistance to B. cinerea to those induced by living bacteria. This suggests the production of bacterial compounds serving as inducers of disease resistance. Using other strains with different characteristics, it is shown that P. fluorescens WCS417 (Pch-deficient), P. putida WCS358 (Pch- and SA-deficient) and P. fluorescens Q2-87 (a DAPG producer) were all capable of inducing resistance to an extent similar to that induced by CHA0. However, in response to WCS417 (Pch-negative) the amount of H2O2 induced is less than for the CHA0. WCS417 induced low phytoalexin levels in cells and lost the capacity to prime for phytoalexins in the leaves. This suggests that, depending on the strain, SA, pyochelin, and DAPG are potentially effective in inducing or priming defence responses. The 7NSK2 mutants, KMPCH (Pch- and Pvd-negative) and KMPCH-567 (Pch-, Pvd-, and SA-negative) induced only partial resistance to B. cinerea. However, the amount of H2O2 triggered by KMPCH and KMPCH-567 was similar to that induced by 7NSK2. Both mutants also led to a low level of phytoalexins in grapevine cells, while KMPCH slightly primed grapevine leaves for enhanced phytoalexins. This highlights the importance of SA, pyochelin, and/or pyoverdin in priming phytoalexin responses and induced grapevine resistance by 7NSK2 against B. cinerea.

A β-1,3 Glucan Sulfate Induces Resistance in Grapevine against Plasmopara viticola Through Priming of Defense Responses, Including HR-like Cell Death

Sulfated laminarin (PS3) has been shown previously to be an elicitor of plant defense reactions in tobacco and Arabidopsis and to induce protection against tobacco mosaic virus. Here, we have demonstrated the efficiency of PS3 in protecting a susceptible grapevine cultivar (Vitis vinifera cv. Marselan) against downy mildew (Plasmopara viticola) under glasshouse conditions. This induced resistance was associated with potentiated H2O2 production at the infection sites, upregulation of defense-related genes, callose and phenol depositions, and hypersensitive response-like cell death. Interestingly, similar responses were observed following P. viticola inoculation in a tolerant grapevine hybrid cultivar (Solaris). A pharmacological approach led us to conclude that both callose synthesis and jasmonic acid pathway contribute to PS3-induced resistance.

Nitric oxide donor seed priming enhances defense responses and induces resistance against pearl millet downy mildew disease

Nitric oxide (NO) donors Nitroso- R-Salt, 2-Nitroso-1-Naphthol and Sodium Nitro Prusside (SNP) were evaluated for their effectiveness in protecting pearl millet [( Pennisetum glaucum L.) R. Br.] plants against downy mildew disease caused by Sclerospora graminicola [(Sacc). Schroet]. Optimization experiments with NO donors showed no adverse effect either on the host or pathogen. Aqueous SNP seed treatment with or without polyethylene glycol (PEG) priming was the most effective in inducing the host resistance against downy mildew both under greenhouse and field conditions. Potassium Ferrocyanide, a structural analog of NO donor lacking NO moiety failed to protect the pearl millet plants from downy mildew indicating a role for NO in induced host resistance. Spatio-temporal studies corroborated that the protection offered by NO donor treatment was systemic in nature and a minimum of 3-day time gap between the inducer treatment and subsequent pathogen inoculation was necessary for maximum resistance development. Disease protection ability of NO donors was also validated as durable in nature. Conversely, prior-treatment with NO scavenger 2-4-carboxyphenyl-4,4,5,5 tetrazoline-1-oxyl-3-oxide potassium salt (C-PTIO) rendered the pearl millet plants relatively susceptible for pathogen infection. Expression of primary defense responses like hypersensitive response, lignin deposition and defense related enzyme phenylalanine ammonialyase −EC 4.3.1.5 (PAL) were enhanced by NO donor treatments.

Resistance proteins: scouts of the plant innate immune system

Recognition of non-self in plants is mediated by specialised receptors that upon pathogen perception trigger induction of host defence responses. Primary, or basal, defence is mainly triggered by trans-membrane receptors that recognise conserved molecules released by a variety of (unrelated) microbes. Pathogens can overcome these basal defences by the secretion of specific effectors. Subsequent recognition of these effectors by specialised receptors (called resistance proteins) triggers induction of a second layer of plant defence responses. These responses are qualitatively similar to primary defence responses; however, they are generally faster and stronger. Here we give an overview of the predicted (domain) structures of resistance proteins and their proposed mode of action as molecular switches of plant innate immunity. We also highlight recent advances revealing that some of these proteins act in the plant nucleus as transcriptional co-regulators and that crosstalk can occur between members of different resistance protein families.

Gene Expression Patterns in Near Isogenic Lines for Wheat Rust Resistance Gene Lr34/Yr18

ABSTRACT The Lr34/Yr18 resistance gene provides durable, adult-plant, slow rusting resistance to leaf rust, yellow rust, and several other diseases of wheat. Flag leaves may exhibit spontaneous leaf tip necrosis and tips are more resistant than leaf bases. Despite the importance of this gene, the mechanism of resistance is unknown. Patterns of expression for 55,052 transcripts were examined by microarray analysis in mock-inoculated flag leaves of two pairs of wheat near isogenic lines for Lr34/Yr18 (Jupateco 73S/Jupateco 73R and Thatcher/Thatcher-Lr34). The Thatcher isolines were also examined for patterns of expression after inoculation with leaf rust. Mock-inoculated leaf tips of resistant plants showed up-regulation of 57 transcripts generally associated with ABA inducibility, osmotic stress, cold stress, and/or seed maturation. Several transcripts may be useful as expression markers for Lr34/Yr18. Five transcripts were also up-regulated in resistant leaf bases. The possible role of these transcripts in resistance is discussed. In mock-inoculated plants, pathogenesis-related (PR) proteins were not up-regulated in resistant flag leaves compared with that in susceptible flag leaves. In inoculated plants, the same set of PR proteins was up-regulated in both resistant and susceptible flag leaves. However, expression was often higher in resistant plants, suggesting a possible role for Lr34/Yr18 in priming of defense responses.

Human defensive behaviors to threat scenarios show parallels to fear- and anxiety-related defense patterns of non-human mammals

Defense patterns of rats and mice have been characterized in terms of the relationships between the type of defensive behavior (e.g. flight, freezing, hiding, defensive threat/attack, and risk assessment) and particular features of the eliciting (threat) stimulus and the situation in which it is encountered. Because the defense systems of rodents serve as major models for investigating and understanding both the physiology and the behavioral expression of emotional response to aversive stimuli, it is essential to evaluate whether these systems show strong parallels in human responsivity to threat.One hundred and sixty male and female undergraduate students read a set of 12 scenarios involving a present or potential threatening conspecific, and chose a primary defensive response to each. These scenarios were designed to vary features known to influence defensive responding in rodents: magnitude of threat; escapability of the situation; ambiguity of the threat stimulus; distance between the threat and the subject; presence of a hiding place. Male and female responses to the various scenarios were highly correlated, except for yell, scream, or call for help which was frequent for females, rare for males. However, a combination of this response category with ‘attack’ showed a highly positive (+0.96) male–female correlation, across scenarios.Correlations between manipulated (and rated) features of the threat stimulus and situation, and type of defensive behavior chosen, strongly supported a view that the patterning of defensive behavior is similar for humans and non-human mammals. Significant correlations were obtained relevant to eight specific hypotheses derived from the animal literature, with some support for two additional hypotheses (non-significant correlations averaging 0.4 or more in expected direction). While three predicted correlations were not supported in these findings, only a single significant correlation was obtained that had not been predicted on the basis of the animal literature. Although the scenario approach, and this application, have specific limitations, these results provide substantial suggestion of congruence between human and non-human mammal defense systems.

Uclacyanins, stellacyanins, and plantacyanins are distinct subfamilies of phytocyanins: plant-specific mononuclear blue copper proteins.

The cDNAs encoding plantacyanin from spinach were isolated and characterized. In addition, four new cDNA sequences from Arabidopsis ESTs were identified that encode polypeptides resembling phytocyanins, plant-specific proteins constituting a distinct family of mononuclear blue copper proteins. One of them encodes plantacyanin from Arabidopsis, while three others, designated as uclacyanin 1, 2, and 3, encode protein precursors that are closely related to precursors of stellacyanins and a blue copper protein from pea pods. Comparative analyses with known phytocyanins allow further classification of these proteins into three distinct subfamilies designated as uclacyanins, stellacyanins, and plantacyanins. This specification is based on (1) their spectroscopic properties, (2) their glycosylation state, (3) the domain organization of their precursors, and (4) their copper-binding amino acids. The recombinant copper binding domain of Arabidopsis uclacyanin 1 was expressed, purified, and shown to bind a copper atom in a fashion known as "blue" or type 1. The mutant of cucumber stellacyanin in which the glutamine axial ligand was substituted by a methionine (Q99M) was purified and shown to possess spectroscopic properties similar to uclacyanin 1 rather than to plantacyanins. Its redox potential was determined by cyclic voltammetry to be +420 mV, a value that is significantly higher than that determined for the wild-type protein (+260 mV). The available structural data suggest that stellacyanins (and possibly other phytocyanins) might not be diffusible electron-transfer proteins participating in long-range electron-transfer processes. Conceivably, they are involved in redox reactions occurring during primary defense responses in plants and/or in lignin formation.

Granular cells are required for encapsulation of foreign targets by insect haemocytes.

Haemocytes play an essential role in defending invertebrates against pathogens and parasites that enter their haemocoel. A primary defense response is encapsulation; a process in which haemocytes attach to the foreign organism and kill it. Whether encapsulation requires cooperation between specific subpopulations of haemocytes is unknown. Using purified subpopulations of haemocytes and an in vitro encapsulation assay, we investigated the process of capsule formation in the insect Pseudoplusia includens. Immunocytochemical staining revealed that capsule formation involves a three step process. Encapsulation began when granular cells attached to the foreign target. This was followed by attachment of multiple layers of plasmatocytes. Termination of capsule formation occurred when a subpopulation of granular cells formed a monolayer around the periphery of the capsule. Neither granular cells nor plasmatocytes were capable of forming a capsule independently. However, plasmatocytes encapsulated targets if granular cells were present or if targets were preincubated in medium conditioned by granular cells. The effect of granular cell-conditioned medium could be blocked by the addition of the cell adhesion recognition sequence, RGDS, but not by RGES. These results demonstrate experimentally that granular cells are required for encapsulation of foreign targets by plasmatocytes in vitro, and that the role of granular cells in this process involves an RGD-dependent cell adhesion mechanism.