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Pathogen Attack (pathogen + attack)

Distribution by Scientific Domains

Life Sciences	83%

Selected Abstracts

Health monitoring of plants by their emitted volatiles: trichome damage and cell membrane damage are detectable at greenhouse scale

ANNALS OF APPLIED BIOLOGY, Issue 3 2009
R.M.C. Jansen
Abstract Pathogen attack and herbivore infestation have a major impact on plant health. In a model study, these two plant health issues were simulated to study whether plant health can be monitored at greenhouse scale through the analysis of volatile organic compounds (VOCs) in greenhouse atmosphere. To simulate pathogen attack and herbivore infestation, we repeatedly stroked the stems of tomato plants (Lycopersicon esculentum) and repeatedly removed their side shoots. In addition, we studied the effect of fruit picking on the concentration of plant-emitted VOCs in greenhouse atmosphere. Analysis of air samples obtained before these treatments revealed up to 17 VOCs that are known to be released from tomato plants, of which the most dominant one was the monoterpene ,-phellandrene. When plants were 7 weeks old, the concentration of this VOC was approximately 0.06 ppbv before treatment. When plants were 12 weeks old, this concentration was raised to approximately 0.14 ppbv. Stroking of the stems, removing the side shoots and fruit picking resulted in an increase in the concentrations of all mono- and most sesquiterpenes up to 60-fold, which was expected because these VOCs are well-known constituents of trichomes. The treatments did not result in substantially increased concentrations of the stress-related compounds ,-copaene, methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast to stroking and fruit picking, shoot removal resulted in the emission of the lipoxygenase-derived product (Z)-3-hexenol in greenhouse atmosphere expressing cell membrane degradation. The findings presented in this paper focus on the feasibility of monitoring plant health through the analysis of VOCs in greenhouse air, but findings might also be relevant for atmospheric chemistry. [source]

Global Change Effects on Plant Chemical Defenses against Insect Herbivores

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 11 2008
M. Gabriela Bidart-Bouzat
Abstract This review focuses on individual effects of major global change factors, such as elevated CO2, O3, UV light and temperature, on plant secondary chemistry. These secondary metabolites are well-known for their role in plant defense against insect herbivory. Global change effects on secondary chemicals appear to be plant species-specific and dependent on the chemical type. Even though plant chemical responses induced by these factors are highly variable, there seems to be some specificity in the response to different environmental stressors. For example, even though the production of phenolic compounds is enhanced by both elevated CO2 and UV light levels, the latter appears to primarily increase the concentrations of flavonoids. Likewise, specific phenolic metabolites seem to be induced by O3 but not by other factors, and an increase in volatile organic compounds has been particularly detected under elevated temperature. More information is needed regarding how global change factors influence inducibility of plant chemical defenses as well as how their indirect and direct effects impact insect performance and behavior, herbivory rates and pathogen attack. This knowledge is crucial to better understand how plants and their associated natural enemies will be affected in future changing environments. [source]

Transcriptome analysis of root-knot nematode functions induced in the early stages of parasitism,

NEW PHYTOLOGIST, Issue 2 2007
G. Dubreuil
Summary ,,Root-knot nematodes of the genus Meloidogyne are obligate biotrophic parasites able to infest > 2000 plant species. The nematode effectors responsible for disease development are involved in the adaptation of the parasite to its host environment and host response modulation. ,,Here, the differences between the transcriptomes of preparasitic exophytic second-stage juveniles (J2) and parasitic endophytic third-stage juveniles (J3) of Meloidogyne incognita were investigated. ,,Genes up-regulated at the endophytic stage were isolated by suppression subtractive hybridization and validated by dot blots and real-time quantitative polymerase chain reaction (PCR). ,,Up-regulation was demonstrated for genes involved in detoxification and protein degradation, for a gene encoding a putative secreted protein and for genes of unknown function. Transcripts of the glutathione S-transferase gene Mi-gsts-1 were 27 times more abundant in J3 than in J2. The observed Mi-gsts-1 expression in the oesophageal secretory glands and the results of functional analyses based on RNA interference suggest that glutathione S-transferases are secreted during parasitism and are required for completion of the nematode life cycle in its host. Secreted glutathione S-transferases may protect the parasite against reactive oxygen species or modulate the plant responses triggered by pathogen attack. [source]

Multivesicular compartments proliferate in susceptible and resistant MLA12 -barley leaves in response to infection by the biotrophic powdery mildew fungus

NEW PHYTOLOGIST, Issue 3 2006
Qianli An
Summary ,,There is growing evidence that multivesicular bodies and cell wall-associated paramural bodies participate in the enhanced vesicle trafficking induced by pathogen attack. ,,Here, we performed transmission electron microscopy in combination with cytochemical localization of H2O2 to investigate multivesicular compartments during establishment of compatible interaction in susceptible barley (Hordeum vulgare) and during hypersensitive response in resistant MLA12 -barley infected by the barley powdery mildew fungus (Blumeria graminis f. sp. hordei). ,,Multivesicular bodies, intravacuolar vesicle aggregates and paramural bodies proliferated in the penetrated epidermal cell during development of the fungal haustorium. These vesicular structures also proliferated at the periphery of intact cells, which were adjacent to the hypersensitive dying cells and deposited cell wall appositions associated with H2O2 accumulation. All plasmodesmata between intact cells and hypersensitive cells were constricted or blocked by cell wall appositions. ,,These results suggest that multivesicular compartments participate in secretion of building blocks for cell wall appositions not only to arrest fungal penetration but also to contain hypersensitive cell death through blocking plasmodesmata. They may also participate in internalization of damaged membranes, deleterious materials, nutrients, elicitors and elicitor receptors. [source]

Oligocarrageenans and tissue-dependant oxidative burst in Solieria chordalis (Rhodophyceae, Gigartinales)

PHYCOLOGICAL RESEARCH, Issue 1 2008
Erwan Ar Gall
SUMMARY The release of hydrogen peroxide by thallus fragments of the rhodophycean Solieria chordalis (C. Agardh) J. Agardh has been documented both in the presence and in the absence of oligosaccharides. Within 1 h, ramuli were able to release large amounts of peroxide in the absence of any chemical stress. Among potential elicitors tested, only degree of polymerization 1 (DP1) and DP7-8 oligo-iota-carrageenans stimulated defense mechanisms in both axes and ramuli as shown by the occurrence of an oxidative burst. Chopping of the tissues had no effect on the intensity of the burst, therefore suggesting that mainly cortical cell layers were involved in the process. After 5 min incubation, a dose of 125 ,g mL,1 of an oligomeric mixture containing a large proportion of DP1 units proved to be sufficient to obtain a maximal response. The intensity of the burst was significantly higher with isolated ramuli than with pieces of the axis, with outer peroxide accumulations reaching 200 nmol g,1 fresh weight of treated tissue. Altogether, our results show that S. chordalis is able to react to a simulated pathogen attack by an oxidative burst and that the capacity to carry out an oxidative burst is stronger in ramuli than in axes. [source]

Genotype and temperature influence pea aphid resistance to a fungal entomopathogen

PHYSIOLOGICAL ENTOMOLOGY, Issue 2 2003
David A. Stacey
Abstract. The influence of temperature on life history traits of four Acyrthosiphon pisum clones was investigated, together with their resistance to one genotype of the fungal entomopathogen Erynia neoaphidis. There was no difference among aphid clones in development rate, but they did differ in fecundity. Both development rate and fecundity were influenced by temperature, but all clones showed similar responses to the changes in temperature (i.e. the interaction term was nonsignificant). However, there were significant differences among clones in susceptibility to the pathogen, and this was influenced by temperature. Furthermore, the clones differed in how temperature influenced susceptibility, with susceptibility rankings changing with temperature. Two clones showed changes in susceptibility which mirrored changes in the in vitro vegetative growth rate of E. neoaphidis at different temperatures, whereas two other clones differed considerably from this expected response. Such interactions between genotype and temperature may help maintain heritable variation in aphid susceptibility to fungal pathogen attack and have implications for our understanding of disease dynamics in natural populations. This study also highlights the difficulties of drawing conclusions about the efficacy of a biological control agent when only a restricted range of pest genotypes or environmental conditions are considered. [source]

Fine-Tuning Plant Defence Signalling: Salicylate versus Jasmonate

PLANT BIOLOGY, Issue 1 2006
G. J. M. Beckers
Abstract: Plant defences against pathogens and herbivorous insects form a comprehensive network of interacting signal transduction pathways. The signalling molecules salicylic acid (SA) and jasmonic acid (JA) play important roles in this network. SA is involved in signalling processes providing systemic acquired resistance (SAR), protecting the plant from further infection after an initial pathogen attack. SAR is long-lasting and provides broad spectrum resistance to biotrophic pathogens that feed on a living host cell. The regulatory protein NPR1 is a central positive regulator of SAR. SA-activated NPR1 localizes to the nucleus where it interacts with TGA transcription factors to induce the expression of a large set of pathogenesis-related proteins that contribute to the enhanced state of resistance. In a distinct signalling process, JA protects the plant from insect infestation and necrotrophic pathogens that kill the host cell before feeding. JA activates the regulatory protein COI1 that is part of the E3 ubiquitin ligase-containing complex SCFCOI1, which is thought to derepress JA-responsive genes involved in plant defence. Both synergistic and antagonistic interactions have been observed between SA- and JA-dependent defences. NPR1 has emerged as a critical modulator of cross-talk between the SA and JA signal and is thought to aid in fine tuning defence responses specific to the encountered attacker. Here we review SA- and JA-dependent signal transduction and summarize our current understanding of the molecular mechanisms of cross-talk between these defences. [source]

Comparative Analysis of Phytophthora infestans Induced Gene Expression in Potato Cultivars with Different Levels of Resistance

PLANT BIOLOGY, Issue 6 2005
B. Ros
Abstract: Differential gene expression was analyzed after infection with Phytophthora infestans in six potato cultivars with different levels of resistance to late blight. To verify the infection of the potato leaflets, the amount of phytopathogen mRNA within the plant material was quantified by real-time quantitative PCR. The expression of 182 genes selected from two subtracted cDNA libraries was studied with cDNA array hybridization using RNA from non-infected and infected potato leaflets. Gene up- and down-regulation were clearly detectable in all cultivars 72 h post inoculation. Gene expression patterns in susceptible cultivars differed from those in potato varieties with a higher level of resistance. In general, a stronger gene induction was observed in the susceptible cultivars compared to the moderately to highly resistant potato varieties. Five genes with the highest homology to stress and/or defence-related genes were induced specifically in the susceptible cultivars. Four genes responded to pathogen attack independently of the level of resistance of the cultivar used, and three genes were repressed in infected tissue of most cultivars. Even in the absence of P. infestans infection, six genes showed higher expression levels in the somewhat resistant cultivars Bettina and Matilda. Possible reasons for the different levels of gene expression are discussed. [source]

The role of NADPH oxidase and MAP kinase phosphatase in UV-B-dependent gene expression in Arabidopsis

PLANT CELL & ENVIRONMENT, Issue 9 2006
IRINA KALBINA
ABSTRACT Plant responses to supplementary UV-B irradiation have been reported to include formation of reactive oxygen species (ROS), hydrogen peroxide, in particular, and regulation by mitogen-activated protein kinase (MAPK) cascades which in turn are fine-tuned by MAPK phosphatases (MKPs). Here we present direct genetic evidence for the involvement of plasma membrane NADPH oxidase, a source of superoxide and hydrogen peroxide in the apoplasts, in UV-B signalling in Arabidopsis thaliana, by analysis of gene expression of the UV-B molecular markers in NADPH oxidase (atrbohD, F and DF) and MAP kinase phosphatase 1 (MKP1) knockout mutants (mkp1). Whereas the NADPH oxidase mutants were affected in UV-B-dependent CHS, PYROA and MEB5.2 gene expression, the mkp1 mutant was affected in the general expression pattern of the pathogenesis-related (PR) and PDF1.2 genes. The results indicate involvement of MKP1 in repressive action on gene expression of more general stress response pathways, similar to those activated by pathogen attack, while NADPH oxidase is involved in quantitative (rather than absolute) regulation of more UV-B-specific genes. The expressions of the molecular markers in the knockout mutant mkp1 and in its complemented lines (lines 6 and 10) were similar, as opposed to the responses of the corresponding wild-type Wassilewskija-4 (Ws-4). Lines 6 and 10 showed much higher MKP1 mRNA than Ws-4 but did not complement the mutant. This suggests a complex dependency of the MAPK phosporylation level of the PR and PDF1.2 genes. Both NADPH oxidase mutants and the mkp1 mutant phenotypically responded to UV-B by growth retardation. [source]

Ascorbic acid, a familiar small molecule intertwined in the response of plants to ozone, pathogens, and the onset of senescence

PLANT CELL & ENVIRONMENT, Issue 8 2004
P. L. CONKLIN
ABSTRACT Ascorbic acid is a well-known antioxidant and cellular reductant with an intimate and complex role in the response of plants to ozone. It is clear from a number of studies that sensitivity to ozone is correlated with total ascorbic acid levels, and that a first line of defence against the reactive oxygen species generated in the apoplastic space by ozone is ascorbic acid. For activity, ascorbic acid must be in the fully reduced state. Therefore, both the rate of ascorbic acid synthesis and recycling via dehydroascorbate and monodehydroascorbate reductases are critical in the maintenance of a high ascorbic acid redox state. Active transport of ascorbic acid across the plasma membrane is necessary to achieve reduction of oxidized ascorbic acid by cytoplasm-localized reductases. It has been known for some time that the chlorotic lesions produced by exposure to ozone are not unlike lesions produced by the hypersensitive response to avirulent pathogen attack. Surprisingly, activation of a defence gene-signalling network by both ozone and pathogens is influenced by the level of ascorbic acid. Indeed, in addition to acting simply as an antioxidant in the apoplastic space, ascorbic acid appears to be involved in a complex phytohormone-mediated signalling network that ties together ozone and pathogen responses and influences the onset of senescence. [source]

Apical leaf necrosis as a defence mechanism against pathogen attack: effects of high nutrient availability on onset and rate of necrosis

PLANT PATHOLOGY, Issue 6 2008
F. Van Den Berg
An outdoor experiment was conducted to increase understanding of apical leaf necrosis in the presence of pathogen infection. Holcus lanatus seeds and Puccinia coronata spores were collected from two adjacent and otherwise similar habitats with differing long-term N fertilization levels. After inoculation, disease and necrosis dynamics were observed during the plant growing seasons of 2003 and 2006. In both years high nutrient availability resulted in earlier disease onset, a higher pathogen population growth rate, earlier physiological apical leaf necrosis onset and a reduced time between disease onset and apical leaf necrosis onset. Necrosis rate was shown to be independent of nutrient availability. The results showed that in these nutrient-rich habitats H. lanatus plants adopted necrosis mechanisms which wasted more nutrients. There was some indication that these necrosis mechanisms were subject to local selection pressures, but these results were not conclusive. The findings of this study are consistent with apical leaf necrosis being an evolved defence mechanism. [source]

Influence of drought, salt stress and abscisic acid on the resistance of tomato to Botrytis cinerea and Oidium neolycopersici

PLANT PATHOLOGY, Issue 2 2006
E. A. Achuo
Abiotic stress may affect plant response to pathogen attack through induced alterations in growth regulator and gene expression. Abscisic acid (ABA) mediates several plant responses to abiotic stress. The effects of drought, salt stress and ABA on the interaction of tomato (Lycopersicon esculentum) with the biotrophic fungus Oidium neolycopersici and the necrotrophic fungus Botrytis cinerea were investigated. Drought stress resulted in a twofold increase in endogenous ABA as well as a 50% reduction in B. cinerea infection and a significant suppression of O. neolycopersici on tomato cv. Moneymaker. Salt stress did not affect B. cinerea infection, but significantly reduced infection by O. neolycopersici, with no obvious increase in endogenous ABA. Compared with the wild type, the ABA-deficient sitiens mutant was more resistant to O. neolycopersici and B. cinerea. Exogenous ABA resulted in increased susceptibility of sitiens to both pathogens, but did not increase the basal susceptibility of wild-type plants. It is concluded that, in tomato, drought and salt stress stimulate different, but possibly overlapping, pathogen-defence pathways which may not necessarily involve ABA. Meanwhile, basal endogenous ABA levels suppress the resistance of tomato to O. neolycopersici and B. cinerea, but an ABA increase above the basal level, resulting from exogenous application, does not increase susceptibility to these pathogens. [source]

Mechanism of cell death and disease resistance induction by transgenic expression of bacterio-opsin

THE PLANT JOURNAL, Issue 5 2002
Dominique Pontier
Summary One of the earliest signal transduction events that trigger the hypersensitive response (HR) of plants against pathogen attack is thought to be an alteration of proton flux across the plasma membrane (PM). However, no direct genetic evidence for the involvement of PM-localised proton channels or pumps in the induction of this response has been reported. We previously showed that expression of the bacterial proton pump bacterio-opsin (bO) in transgenic plants resulted in the spontaneous activation of the HR. Here we show that the bO protein is likely localised to the PM in transgenic tobacco plants. Furthermore, mutational analysis shows that induction of the HR by bO expression is dependent upon the capability of bO to translocate protons. Although bO functions as a light-driven proton pump in Halobacteria when assembled with retinal, we also show by mutational analysis that this chromophore binding is unnecessary for its in planta activity. Taken together, our results suggest that expression of bO in plants leads to the insertion of a passive proton channel into the PM. The activity of this channel in the PM results in spontaneous activation of cell death and HR-associated phenotypes including enhanced resistance to a broad spectrum of plant pathogens. Our work provides direct molecular evidence to support a working model in which alterations in ionic homeostasis at the level of the PM may work as one of the critical steps in the signalling pathway for the activation of the HR. [source]

Health monitoring of plants by their emitted volatiles: trichome damage and cell membrane damage are detectable at greenhouse scale

Enhancing the natural defences and barrier protection of aquaculture species

AQUACULTURE RESEARCH, Issue 3 2010
John W Sweetman
Abstract The promotion of nutritional strategies that optimize natural defence mechanisms in fish is of critical importance in producing robust juveniles and adult fish. These animals are more capable of minimizing the impact of opportunistic pathogen attack, thus improving liveability and performance characteristics. The importance of the piscine gastrointestinal tract as a major endocrine and osmoregulatory organ is well reported as is its function as a defensive barrier to pathogen attack. Investigations using the inclusion of a specific structural form of mannan oligosaccharide have been shown to improve the performance parameters, immune status, and gut morphology and improve an important aspect of barrier protection through the enhancement of mucal production in a number of aquaculture species. The selenium status of an animal is pivotal in determining the success of the innate and adaptive immune response of the animal, and the use of an organic selenium source, in the form of a selenoyeast, has been shown to improve enzyme function and tissue uptake. The antioxidant role of many of the selenoptroteins and the role of selenium in the glutathione peroxidase enzyme pathways involved in the control of oxidative stress is critical if oxidative damage and cell membrane lipid peroxidation are to be prevented. The use of these compounds as feed additives has important implications for health management in commercial aquaculture facilities. Further research is needed to evaluate the benefits offered by a range of commercial products. [source]

Layers of defense responses to Leptosphaeria maculans below the RLM1 - and camalexin-dependent resistances

NEW PHYTOLOGIST, Issue 2 2009
Mattias Persson
Summary ,,Plants have evolved different defense components to counteract pathogen attacks. The resistance locus resistance to Leptosphaeria maculans 1 (RLM1) is a key factor for Arabidopsis thaliana resistance to L. maculans. The present work aimed to reveal downstream defense responses regulated by RLM1. ,,Quantitative assessment of fungal colonization in the host was carried out using quantitative polymerase chain reaction (qPCR) and GUS expression analyses, to further characterize RLM1 resistance and the role of salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) in disease development. Additional assessments of A. thaliana mutants were performed to expand our understanding of this pathosystem. ,,Resistance responses such as lignification and the formation of vascular plugs were found to occur in an RLM1 -dependent manner, in contrast to the RLM1 -independent increase in reactive oxygen species at the stomata and hydathodes. Analyses of mutants defective in hormone signaling in the camalexin-free rlm1Lerpad3 background revealed a significant influence of JA and ET on symptom development and pathogen colonization. ,,The overall results indicate that the defense responses of primary importance induced by RLM1 are all associated with physical barriers, and that responses of secondary importance involve complex cross-talk among SA, JA and ET. Our observations further suggest that ET positively affects fungal colonization. [source]

Proteome, salicylic acid, and jasmonic acid changes in cucumber plants inoculated with Trichoderma asperellum strain T34

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 21 2007
Guillem Segarra
Abstract Trichoderma spp. is one of the most commonly used biological control agents against plant pathogens. This fungus produces changes in plant metabolism, thus increasing growth and enhancing resistance to biotic and abiotic stresses. However, its modes of action remain to be defined. In the first hours of interaction between cucumber plant roots and Trichoderma asperellum strain T34, salicylic and jasmonic acid levels and typical antipathogenic peroxidase activity increase in the cotyledons to different degrees depending on the applied concentration of the fungi. The use of 2-DE protein profiling and MS analysis allowed us to identify 28 proteins whose expression was affected in cotyledons after cucumber root colonization by Trichoderma applied at high concentrations: 17 were found to be up-regulated while 11 were down-regulated. Proteins involved in ROS scavenging, stress response, isoprenoid and ethylene biosynthesis, and in photosynthesis, photorespiration, and carbohydrate metabolism were differentially regulated by Trichoderma. The proteome changes found in this study help to give an understanding of how Trichoderma -treated plants become more resistant to pathogen attacks through the changes in expression of a set of defence-oriented proteins which can directly protect the plant or switch the metabolism to a defensive, nonassimilatory state. [source]