Mechanism Of Induced Resistance Research Articles

Differential susceptibility of Morettini pears to blue mold caused by Penicillium expansum

Pear fruit (Pyrus communis L. cv Beurre Precoce Morettini) developing on the outside of canopy and exposed to sunlight acquires a bright redness on the exposed side, compared to the green peel fruit that develop within the canopy. At harvest, the main physicochemical parameters of the red and green side of the fruit, including firmness, brix and titratable acidity, were similar in pears harvested at the same day and stage of maturity. However, it was observed that fruits with a red side or that mostly green showed a different response to biotic stress, namely to pathogenic fungi attack. Actually, after 7 days under shelf-life conditions, red fruits demonstrated to be more resistant than green ones when challenged with a postharvest Penicillium expansum inoculation. Significant differences were observed in antioxidant activity and total phenolic compounds between both sides of the fruits. Several polyphenols related to mechanisms of induced resistance against fungal plant pathogens were identified in the extracts, such as catechin, quercetin, quinic acid or caffeoylquinic acid. These results suggest that the accumulation of phenolic compounds triggered by sun exposure may be one of the mechanisms responsible for the increased resistance of red-skinned Morettini pears.

Biochemical mechanisms of induced resistance by rhizobial lipopolysaccharide in pea against crenate broomrape

Lipopolysaccharides (LPS) isolated from rhizobia have been demonstrated as inducer of systemic resistance against plant diseases. The role of bacterial LPS in induced resistance in plant has not been extensively reported. The capacity of Rhizobium leguminosarum Mabrouk et al. 2007 strain P.SOM to reduce parasitism of pea by Orobanche crenata Mabrouk et al. 2007 was previously demonstrated under greenhouse and field trials. The objective of this study was to examine the capacity of LPS isolated from strain P.SOM to induce resistance in pea against crenate broomrape, with more emphasis on the biochemical mechanisms of host plant defense reaction induced by LPS. Root chamber experiments using Petri dishes revealed that LPS reduce broomrape seed germination and restricted the broomrape attachment to the host root as well as retarded tubercle formation and development. In pot experiments, pea roots treatment with LPS reduced the total number of broomrape by up to 95 %. No biomass reduction of pea was observed after application of LPS. Broomrape necrosis was observed both before and after parasite attachment to treated pea roots in Petri dishes and pots experiments. Concomitantly, reduction in infection was accompanied by enhanced phenylalanine ammonia lyase, peroxidase, and polyphenoloxidase activities. As a consequence, the derived products, phenolics, and pisatin accumulated in response to LPS and conferred mechanical and chemical barriers to the invading parasite. Our findings indicate an important role for LPS as a direct inducer of defenses in pea against broomrape.

EFEITO DE EXTRATOS DE Allamanda blanchetti NO CONTROLE DE Alternaria brassicicola EM MUDAS DE COUVE-MANTEIGA

RESUMO: O objetivo do presente trabalho foi avaliar o efeito do extrato de uma planta nativa da caatinga (Allamanda blanchetti) no controle do fungo Alternaria brassicicola quanto à indução de mecanismos de resistência em mudas de couve-manteiga e ação fungitóxica diretaEm condições de casa de vegetação, as mudas de couve-manteiga foram pulverizadas com os extratos de A. blanchetti extraídos a quente e a frio, nas concentrações 0, 100, 500 e 1000 ppm. Avaliações da severidade da doença foram realizadas a 5, 6, 7, 8, 9 e 10 dias após a inoculação. Peroxidases foram analisadas em cinco tempos, quais sejam, 0, 24, 72, 120 e 168 horas após a pulverização das mudas com os extratos. Além disso, fora avaliado também a capacidade dos extratos a quente e a frio a 0, 100, 500 e 1000 ppm em inibir a germinação dos esporos de A. brassicicola. As concentrações de 1000 ppm dos extratos a quente e a frio foram as mais eficientes no controle da doença. O extrato de A. blanchetti induziu aumento da atividade de peroxidase às 24 horas após a aplicação dos tratamentos e promoveu inibição da germinação dos esporos de A. brassicicola. Estes resultados indicam o potencial de A. blanchetti no controle de A. brassicicola, tanto pela ação direta quanto pela ativação de mecanismos de defesa.

Regulation of inducible enzymes and suppression of anthracnose using submicron chitosan dispersions

The mechanism of suppression of Colletotrichum gloeosporioides was studied by using submicron chitosan dispersions. In vitro and in vivo experiments showed that mycelial growth and disease incidence/ severity were significantly (P<0.05) suppressed in 600nm submicron chitosan dispersion at 1% chitosan concentration. Field trials showed that host resistance was stimulated in dragon fruit plants at all the submicron chitosan dispersions (SCD) used. Results showed that the application of SCD significantly enhanced the production of plant-defense related enzymes such as PO, PPO and PAL. A further increase in inducible compounds and PR proteins was observed in plants inoculated with C. gloeosporioides. Increase in inducible compounds and delayed symptoms of anthracnose indicated the possible mechanism of induced resistance. However, the resistance decreased with the passage of time which could be due to highly stressed environment of the plants. Therefore, it is suggested that the plants should be sprayed with SCD to sustain the absolute effect.

NH4+ protects tomato plants against Pseudomonas syringae by activation of systemic acquired acclimation.

NH4 (+) nutrition provokes mild toxicity by enhancing H2O2 accumulation, which acts as a signal activating systemic acquired acclimation (SAA). Until now, induced resistance mechanisms in response to an abiotic stimulus and related to SAA were only reported for exposure to a subsequent abiotic stress. Herein, the first evidence is provided that this acclimation to an abiotic stimulus induces resistance to later pathogen infection, since NH4 (+) nutrition (N-NH4 (+))-induced resistance (NH4 (+)-IR) against Pseudomonas syringae pv tomato DC3000 (Pst) in tomato plants was demonstrated. N-NH4 (+) plants displayed basal H2O2, abscisic acid (ABA), and putrescine (Put) accumulation. H2O2 accumulation acted as a signal to induce ABA-dependent signalling pathways required to prevent NH4 (+) toxicity. This acclimatory event provoked an increase in resistance against later pathogen infection. N-NH4 (+) plants displayed basal stomatal closure produced by H2O2 derived from enhanced CuAO and rboh1 activity that may reduce the entry of bacteria into the mesophyll, diminishing the disease symptoms as well as strongly inducing the oxidative burst upon Pst infection, favouring NH4 (+)-IR. Experiments with inhibitors of Put accumulation and the ABA-deficient mutant flacca demonstrated that Put and ABA downstream signalling pathways are required to complete NH4 (+)-IR. The metabolic profile revealed that infected N-NH4 (+) plants showed greater ferulic acid accumulation compared with control plants. Although classical salicylic acid (SA)-dependent responses against biotrophic pathogens were not found, the important role of Put in the resistance of tomato against Pst was demonstrated. Moreover, this work revealed the cross-talk between abiotic stress acclimation (NH4 (+) nutrition) and resistance to subsequent Pst infection.

Menadione Sodium Bisulphite (MSB) enhances the resistance response of tomato, leading to repel mollusc pests.

Snails and slugs are terrestrial gastropods representing an important biotic stress that adversely affects crop yields. These pests are typically controlled with molluscicides, which produce pollution and toxicity and further induce the evolution of resistance mechanisms, making pest management even more challenging. In our work, we have assessed the efficacy of two different plant defence activators, menadione sodium bisulphite (MSB) and 1,2,3-benzothiadiazole-7-thiocarboxylic acid S-methyl ester (BTH), as inducers of resistance mechanisms of the model plant for defence, Solanum lycopersicum, against the generalist mollusc Theba grasseti (Helicidae). The study was designed to test the feeding behaviour and choice of snails, and also to analyse the expression profile of different genes specifically involved in defence against herbivores and wounds. Our data suggest that, through the downregulation of the terpene volatile genes and the production of proteinase inhibitors, treated MSB plants may be less apparent to herbivores that use herbivore-induced plant volatiles for host location. By contrast, BTH was not effective in the treatment of the pest, probably owing to an antagonistic effect derived from the induction of both salicylic-acid-dependent and jasmonic-acid-dependent pathways. This information is crucial to determine the genetic basis of the choice of terrestrial gastropod herbivores in tomato, providing valuable insight into how the plant defence activators could control herbivore pests in plants. Our work not only reports for the first time the interaction between tomato and a mollusc pest but also presents the action of two plant defence inductors that seems to produce opposed responses by inducing resistance mechanisms through different defence pathways.

Molecular mechanisms of clarithromycin resistance in Mycobacterium abscessus complex clinical isolates from Venezuela.

In this study, 26 clinical isolates of Mycobacterium abscessus complex strains were characterised using available identification algorithms for the three species (M. abscessus, M. massiliense and M. bolletii) and the genotypic characteristics of clarithromycin (CLR) resistance were determined. Strains were identified by PCR restriction fragment length polymorphism analysis of the hsp65 and erm(41) gene sequences. Susceptibility to CLR was determined by the broth microdilution method. The mechanism of resistance to this macrolide was evaluated by sequencing the erm(41) and rrl genes. Mutations and/or deletions associated with resistance to CLR as determined in this study were those that have been previously described. No constitutive resistance to CLR was found, however 35% (9/26) of the M. abscessus complex strains tested had a functional inducible erm(41) gene. Based on sequencing of this gene, the strains of M. abscessus were separated into six sequevars, of which only two are consistent with those previously reported. In conclusion, we demonstrated that the low percentage of strains with a resistant phenotype to CLR was due only to an inducible resistance mechanism conferred by the erm(41) gene and not to mutations in the rrl gene. CLR can still be useful for treatment in some Venezuelan patients infected with a member of the M. abscessus group, but drug resistance testing and/or molecular analysis must precede the prescription of this antibiotic.

Biological control of southern corn leaf blight by Trichoderma atroviride SG3403

Trichoderma atroviride SG3403 showed high biocontrol activity against southern corn leaf blight (SCLB; pathogen: Cochliobolus heterostrophus). T. atroviride SG3403 could cause death of C. heterostrophus race O hypha on plates. Spraying T. atroviride SG3403 conidia suspension over maize seedling leaves protected the corn from SCLB infection. Biocontrol effect lasted for 30 days in the field. Trichoderma strain was able to induce resistance response in corn leaves against pathogen infection. In corn leaves treated with T. atroviride SG3403, the enzyme activities of phenylalanine ammonia lyase (PAL) and superoxide dismutase (SOD) reached the highest at 24 h, enzyme activity of catalase (CAT) reached the highest at 36 h after inoculation of pathogen C. heterostrophus race O. RNA expression levels of Pal, Sod and Cat (which synthesis enzyme PAL, SOD and CAT) were also upregulated and corresponded to the enzyme activity at the same time point. Enzyme activities and corresponding genes expression induced by Trichoderma SG3403 was more obvious than that induced by pathogen only, which implies that T. atroviride SG3403 induced corn defense gene expression against pathogen infection. Thus, induced resistance mechanism was possibly involved in the biocontrol of SCLB by T. atroviride SG3403.

Methyl jasmonate induces a hypersensitive-like response of grapevine in the absence of avirulent pathogens

Methyl jasmonate (MeJA), a common plant secondary compound, when applied to the surface of grapevine leaves, caused the formation of lesions that mimic a typical hypersensitive response. Sustained exposure of grapevines to 50 µM MeJA provoked tissue damage, stimulated salicylic acid production, and expression of defense-related genes. Besides these local responses, after several days systemic expression of defense-related genes was induced as well, Thus, grapevine cells that perceived MeJA generated a cascade of events acting at local, short and long distances and causing the coordinated expression of specific defense responses with a timing and magnitude similar to the hypersensitive response against pathogens, MeJA represents a powerful tool to investigate the signals and their respective pathways involved in mechanism of induced disease resistance of grapevine.

Inducible Expression of a Resistance-Nodulation-Division-Type Efflux Pump in Staphylococcus aureus Provides Resistance to Linoleic and Arachidonic Acids.

Although Staphylococcus aureus is exposed to antimicrobial fatty acids on the skin, in nasal secretions, and in abscesses, a specific mechanism of inducible resistance to this important facet of innate immunity has not been identified. Here, we have sequenced the genome of S. aureus USA300 variants selected for their ability to grow at an elevated concentration of linoleic acid. The fatty acid-resistant clone FAR7 had a single nucleotide polymorphism resulting in an H₁₂₁Y substitution in an uncharacterized transcriptional regulator belonging to the AcrR family, which was divergently transcribed from a gene encoding a member of the resistance-nodulation-division superfamily of multidrug efflux pumps. We named these genes farR and farE, for regulator and effector of fatty acid resistance, respectively. Several lines of evidence indicated that FarE promotes efflux of antimicrobial fatty acids and is regulated by FarR. First, expression of farE was strongly induced by arachidonic and linoleic acids in an farR-dependent manner. Second, an H₁₂₁Y substitution in FarR resulted in increased expression of farE and was alone sufficient to promote increased resistance of S. aureus to linoleic acid. Third, inactivation of farE resulted in a significant reduction in the inducible resistance of S. aureus to the bactericidal activity of 100 μM linoleic acid, increased accumulation of [(14)C]linoleic acid by growing cells, and severely impaired growth in the presence of nonbactericidal concentrations of linoleic acid. Cumulatively, these findings represent the first description of a specific mechanism of inducible resistance to antimicrobial fatty acids in a Gram-positive pathogen. Staphylococcus aureus colonizes approximately 25% of humans and is a leading cause of human infectious morbidity and mortality. To persist on human hosts, S. aureus must have intrinsic defense mechanisms to cope with antimicrobial fatty acids, which comprise an important component of human innate defense mechanisms. We have identified a novel pair of genes, farR and farE, that constitute a dedicated regulator and effector of S. aureus resistance to linoleic and arachidonic acids, which are major fatty acids in human membrane phospholipid. Expression of farE, which encodes an efflux pump, is induced in an farR-dependent mechanism, in response to these antimicrobial fatty acids that would be encountered in a tissue abscess.

Detection of vancomycin resistances in enterococci within 3 ½ hours.

Vancomycin resistant enterococci (VRE) constitute a challenging problem in health care institutions worldwide. Novel methods to rapidly identify resistances are highly required to ensure an early start of tailored therapy and to prevent further spread of the bacteria. Here, a spectroscopy-based rapid test is presented that reveals resistances of enterococci towards vancomycin within 3.5 hours. Without any specific knowledge on the strain, VRE can be recognized with high accuracy in two different enterococci species. By means of dielectrophoresis, bacteria are directly captured from dilute suspensions, making sample preparation very easy. Raman spectroscopic analysis of the trapped bacteria over a time span of two hours in absence and presence of antibiotics reveals characteristic differences in the molecular response of sensitive as well as resistant Enterococcus faecalis and Enterococcus faecium. Furthermore, the spectroscopic fingerprints provide an indication on the mechanisms of induced resistance in VRE.

P070 Studies on the mechanisms of induced resistance in rice

P070 Studies on the mechanisms of induced resistance in rice

P071 Studies on the mechanisms of induced resistance in tomato

P071 Studies on the mechanisms of induced resistance in tomato

Intrinsic and induced drug resistance mechanisms: in silico investigations at the cellular and tissue scales.

Multiple cellular drug resistance mechanisms are present in a broad range of tumour types and act to counteract the effects of drugs. There are independent mechanisms by which drug resistance occurs; these include (i) the multi-drug resistance mechanism involving upregulation of ABC transporter proteins and (ii) intracellular mechanisms which sequester/degrade/detoxify drugs. In addition, drug resistance mechanisms could be either intrinsic, or directly induced by the drug. In this paper we focus on the behaviour of intrinsic and induced variants of these resistance mechanisms in solid tumours, by systematically elucidating their cellular and tissue level effects with an aim to bridge the gap between cell and tissue levels. This is achieved in a controlled in silico setting, which allows for an investigation of the interplay between transport, resistance pathways, and tissue level effects. Overall the paper (i) provides insights into the tissue level functioning of widespread classes of intracellular resistance mechanisms, showing important differences, (ii) systematically elucidates the difference between intrinsic and induced drug resistance mechanisms at the cell and tissue levels, (iii) demonstrates how spatial heterogeneity in intrinsic resistance in cells can significantly affect the response of solid tumours to drugs, and (iv) examines how different independent resistance mechanisms work in concert, to counteract drug dosages in tumours.

Field Screening of Mungbean Genotypes and the Role of Total Soluble Sugars and Phenols against Powdery Mildew Resistance

Powdery mildew of mungbean caused by Erysiphe polygoni DC may cause yield loss up to 20–40%. Mungbean (51) genotypes were screened in three consecutive seasons under natural epiphytotic conditions. Out of 51 genotypes, TM-96-2 exhibited highly resistance, nine as resistance, five as moderately resistance, 16 as susceptible and 20 as highly susceptible reactions for powdery mildew. On the basis of field screening, two resistant and 10 susceptible genotypes were selected for the study of relationship between induced resistance mechanism with total soluble sugars and phenol contents in plants. The resistant genotypes contained high level of phenols than the susceptible genotypes while, susceptible genotypes contained high level of total soluble sugars than the resistant genotypes.

Uncovering the defence responses of Eucalyptus to pests and pathogens in the genomics age.

Long-lived tree species are subject to attack by various pests and pathogens during their lifetime. This problem is exacerbated by climate change, which may increase the host range for pathogens and extend the period of infestation by pests. Plant defences may involve preformed barriers or induced resistance mechanisms based on recognition of the invader, complex signalling cascades, hormone signalling, activation of transcription factors and production of pathogenesis-related (PR) proteins with direct antimicrobial or anti-insect activity. Trees have evolved some unique defence mechanisms compared with well-studied model plants, which are mostly herbaceous annuals. The genome sequence of Eucalyptus grandis W. Hill ex Maiden has recently become available and provides a resource to extend our understanding of defence in large woody perennials. This review synthesizes existing knowledge of defence mechanisms in model plants and tree species and features mechanisms that may be important for defence in Eucalyptus, such as anatomical variants and the role of chemicals and proteins. Based on the E. grandis genome sequence, we have identified putative PR proteins based on sequence identity to the previously described plant PR proteins. Putative orthologues for PR-1, PR-2, PR-4, PR-5, PR-6, PR-7, PR-8, PR-9, PR-10, PR-12, PR-14, PR-15 and PR-17 have been identified and compared with their orthologues in Populus trichocarpa Torr. & A. Gray ex Hook and Arabidopsis thaliana (L.) Heynh. The survey of PR genes in Eucalyptus provides a first step in identifying defence gene targets that may be employed for protection of the species in future. Genomic resources available for Eucalyptus are discussed and approaches for improving resistance in these hardwood trees, earmarked as a bioenergy source in future, are considered.

Analysis of Clonostachys rosea-induced resistance to tomato gray mold disease in tomato leaves.

Tomato gray mold disease, caused by Botrytis cinerea, is a serious disease in tomato. Clonostachys rosea is an antagonistic microorganism to B. cinerea. To investigate the induced resistance mechanism of C. rosea, we examined the effects of these microorganisms on tomato leaves, along with changes in the activities of three defense enzymes (PAL, PPO, GST), second messengers (NO, H2O2, O2 −) and phytohormones (IAA, ABA, GA3, ZT, MeJA, SA and C2H4). Compared to the control, all treatments induced higher levels of PAL, PPO and GST activity in tomato leaves and increased NO, SA and GA3 levels. The expression of WRKY and MAPK, two important transcription factors in plant disease resistance, was upregulated in C. rosea- and C. rosea plus B. cinerea-treated samples. Two-dimensional gel electrophoresis analysis showed that two abundant proteins were present in the C. rosea plus B. cinerea-treated samples but not in the other samples. These proteins were determined (by mass spectrum analysis) to be LEXYL2 (β-xylosidase) and ATP synthase CF1 alpha subunit. Therefore, C. rosea plus B. cinerea treatment induces gray mold resistance in tomato. This study provides a basis for elucidating the mechanism of C. rosea as a biocontrol agent.

Intracellular interactions involved in induced systemic resistance in tomato

Induced resistance is based upon modulations in expression of defense related genes. Those complex changes in genome expression lead plant metabolites toward defensive state. Presently, a study has been carried out to investigate mechanism of induced resistance (IR) in tomato under the influence of a non-pathogenic fungal inducer (Penicillium oxalicum) against Alternaria alternata.Expression of different PR genes was altered due to application of P. oxalicum or A. alternata with concomitant alterations in plant pathways. Enhanced expression of all eight PR genes was recorded by application of either fungal species. In resistant variety, fungal species showed synergistic effects on expression of seven PR genes i.e. P69 acidic, PR1 basic, PR2 basic, PR2 acidic, chitinase acidic, metallothionein and PR5. Chitinase basic was the only gene which was upregulated up to a specific level by application of either single or both fungal species.Expression of PR genes was also analyzed in terms of their respective metabolic pathways and it was recorded that Phytochelatin biosynthesis pathway (PCB) and Salicylic acid pathway (SA) were directly interlinked with each other. Moreover, their direct relation was strengthened due to either application of single fungal species or both. Jasmonic acid pathway (JA) was inversely associated with SA as well as PCB. After a certain elevation in SA, increase in IR was due to decreased level of JA.Study will help investigators to design fundamental rules of IR and alterations in associated metabolic pathways. It also strongly recommends P. oxalicum as an inducer to protect tomato plants from fungal pathogens.

English

Our previous studies showed that living and heat-killed cells of the Rhizobium leguminosarum strain P.SOM induce in pea roots systemic resistance to infection by Orobanche crenata. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. leguminosarum-pea interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to pea roots, and tested for activity as an inducer of plant resistance to broomrape. Whereas EPS did not affect O. crenata infection, LPS reduced Orobanche infection significantly in concentrations as low as 1 and 0.5 mg ml-1. In contrast these compounds did not influence parasite germination induced by the artificial stimulant, GR24. Our results show that soil treatments with LPS resulted in a highly significant reduction of O. crenata infection of pea roots. The results clearly showed that LPS of R. leguminosarum P.SOM act as the inducing agent of systemic resistance in pea roots against Orobanche. Key words: Rhizobium leguminosarum, Lipopolysaccharides, Exopolysaccharides, Induced resistance, Orobanche crenata, Pea.

Induction of lignin and pathogenesis related proteins in dragon fruit plants in response to submicron chitosan dispersions

Chitosan is capable of triggering the induction of defence responses of the plants. This study was carried out to investigate in vitro and in vivo antifungal activity of submicron chitosan dispersions and also to determine the mechanism of induced resistance in dragon fruit plants by strengthening of cell wall and production of pathogenesis related proteins. Highest inhibition in radial mycelial growth (90.2%) was obtained by 600 nm droplet size at 1.0% chitosan concentration. None of the emulsifiers showed any antifungal effect during in vitro studies. Field studies showed the reduction of 22% disease incidence and 66% disease severity in anthracnose on dragon fruit plants treated with 600 nm droplet size as compared to control plants after one month of assessment. Lignin contents in cell wall of dragon fruit plants increased 2 folds in plants treated with 1.0% chitosan at 600 nm droplet size while 11 and 10 folds increase in β-1,3-glucanase and chitinase activity, respectively was also recorded in the plants inoculated with Colletotrichum gloeosporioides. The accumulation of lignin and higher level activity of pathogenesis related proteins in response to submicron chitosan dispersions may bolster in mounting effective resistance against the devastating disease of anthracnose.