Mechanism of resistance to Cucumber mosaic virus elicited by inoculation with Bacillus subtilis subsp. subtilis. - Related Documents




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878501.0000Mechanism of resistance to Cucumber mosaic virus elicited by inoculation with Bacillus subtilis subsp. subtilis. BACKGROUND: Systemic resistance stimulated by rhizosphere bacteria is an important strategy for the management of plant viruses. The efficacy of Bacillus subtilis subsp. subtilis was assessed for protection of cucumber and Arabidopsis against Cucumber mosaic virus (CMV). Moreover, transcriptomic analysis was carried out for A. thaliana colonized with B. subtilis subsp. subtilis and infected with CMV. RESULTS: Treatment with a cell suspension of Bacillus revealed a significant reduction of CMV severity in comparison to their control. All Arabidopsis mutants treated with B. subtilis showed a clear reduction in CMV accumulation. Disease severity data and virus concentration titer measurements correlated with gene up-regulation in microarray and reverse transcription quantitative polymerase chain reaction (RT-qPCR) experiments. Bacillus treatment increased Arabidopsis growth characteristics (fresh and dry weights and number of leaflets) under pot conditions. The molecular mechanisms by which Bacillus activated resistance to CMV were investigated. Using the microarray hybridization technique, we were able to determine the mechanism of resistance elicited by B. subtilis against CMV. The transcriptomic analysis confirmed the up-regulation of more than 250 defense-related genes in Arabidopsis expressing induced systemic resistance (ISR). RT-qPCR results validated the overexpression of defense genes (YLS9 and PR1 in Arabidopsis and PR1 and LOX in cucumber), implying their important roles in the stimulated defense response. CONCLUSION: Through the study of microarray and RT-qPCR analyses, it can be concluded that the overexpression of pathogenesis-related genes was necessary to stimulate CMV defense in cucumber and Arabidopsis by B. subtilis subsp. subtilis. © 2021 Society of Chemical Industry.202234437749
878410.9997Bacillus firmus Strain I-1582, a Nematode Antagonist by Itself and Through the Plant. Bacillus firmus I-1582 is approved in Europe for the management of Meloidogyne on vegetable crops. However, little information about its modes of action and temperature requirements is available, despite the effect of these parameters in its efficacy. The cardinal temperatures for bacterial growth and biofilm formation were determined. The bacteria was transformed with GFP to study its effect on nematode eggs and root colonization of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) by laser-scanning confocal microscopy. Induction of plant resistance was determined in split-root experiments and the dynamic regulation of genes related to jasmonic acid (JA) and salicylic acid (SA) by RT-qPCR at three different times after nematode inoculation. The bacteria was able to grow and form biofilms between 15 and 45°C; it degraded egg-shells and colonized eggs; it colonized tomato roots more extensively than cucumber roots; it induced systemic resistance in tomato, but not in cucumber; SA and JA related genes were primed at different times after nematode inoculation in tomato, but only the SA-related gene was up-regulated at 7 days after nematode inoculation in cucumber. In conclusion, B. firmus I-1582 is active at a wide range of temperatures; its optimal growth temperature is 35°C; it is able to degrade Meloidogyne eggs, and to colonize plant roots, inducing systemic resistance in a plant dependent species manner.202032765537
878320.9997Characterization and potential of plant growth promoting rhizobacteria isolated from native Andean crops. Bacteria isolated from soil and rhizosphere samples collected in Peru from Andean crops were tested in vitro and in vivo to determine their potential as plant growth promoters and their ability to induce systemic resistance to Alternaria alternata in tomato plants. The isolates were identified by sequencing their 16S ribosomal RNA gene. Test for phosphate solubilization, and indolacetic acid were also carried out, together with in vitro antagonism assays in dual cultures towards the plant pathogens Fusarium solani, A. alternata and Curvularia lunata. The three most promising isolates (Pa15, Ps155, Ps168) belonged to the genus Pseudomonas. Further assays were carried out with tomato plants to assess their plant protection effect towards A. alternata and as growth promoters. Inoculation of tomato seeds with all isolates significantly enhanced seed germination, plantlets emergence and plant development. Bacterial inoculation also reduce damage level caused by A. alternata. The expression levels of three tomato genes involved in the jasmonate (AOS), ethylene responsive (ERF-2) and pathogenesis related (PR-P2) pathways were determined in plants challenged with A. alternata, alone or with each bacterial isolate, respectively. Results showed that at 24 h after infection, in absence of the pathogen, the expression level of the tested genes was very low. The presence of A. alternata alone and in combination with bacteria increased the transcripts of all genes. Data showed a potential of best performing isolate Ps168 to sustain tomato plants nutrition and activate defense-related genes for protection by pathogenic fungi.201729079927
878230.9996Antagonistic bacterium Bacillus amyloliquefaciens induces resistance and controls the bacterial wilt of tomato. BACKGROUND: Bacterial wilt caused by Ralstonia solanacearum (RS) is a serious threat for agricultural production. In this study, Bacillus amyloliquefaciens strains CM-2 and T-5 antagonistic to RS were used to create bioorganic fertilisers to control tomato wilt under greenhouse conditions. The possible mechanism of resistance inducement by the antagonistic bacteria was also evaluated. RESULTS: The application of bioorganic fertilisers significantly reduced incidences of tomato wilt (by 63-74%), promoted plant growth and significantly reduced the RS populations in rhizosphere compared with the control. Both strains CM-2 and T-5 applied with bioorganic fertilisers survived well in the tomato rhizosphere. Tomato seedlings treated with cell suspension of T-5 followed by challenge inoculation with RS increased the activities of polyphenol oxidase, phenylalanine ammonia lyase and peroxidase compared with the untreated control. Furthermore, the expressions of the marker genes responsible for synthesis of phytohormones salicylic acid, ethylene and jasmonic acid in seedlings treated with T-5 in response to inoculated pathogen were significantly higher. CONCLUSIONS: This study suggests that strains CM-2 and T-5 containing bioorganic fertilisers effectively control tomato wilt. Increased enzyme activities and expression of defence genes in plants indicated that the antagonistic bacteria induced plant resistance, which was the potential biocontrol mechanism of tomato wilt.201323519834
32740.9995Natural variation in RPS2-mediated resistance among Arabidopsis accessions: correlation between gene expression profiles and phenotypic responses. Natural variation in gene expression (expression traits or e-traits) is increasingly used for the discovery of genes controlling traits. An important question is whether a particular e-trait is correlated with a phenotypic trait. Here, we examined the correlations between phenotypic traits and e-traits among 10 Arabidopsis thaliana accessions. We studied defense against Pseudomonas syringae pv tomato DC3000 (Pst), with a focus on resistance gene-mediated resistance triggered by the type III effector protein AvrRpt2. As phenotypic traits, we measured growth of the bacteria and extent of the hypersensitive response (HR) as measured by electrolyte leakage. Genetic variation among accessions affected growth of Pst both with (Pst avrRpt2) and without (Pst) the AvrRpt2 effector. Variation in HR was not correlated with variation in bacterial growth. We also collected gene expression profiles 6 h after mock and Pst avrRpt2 inoculation using a custom microarray. Clusters of genes whose expression levels are correlated with bacterial growth or electrolyte leakage were identified. Thus, we demonstrated that variation in gene expression profiles of Arabidopsis accessions collected at one time point under one experimental condition has the power to explain variation in phenotypic responses to pathogen attack.200718083910
32450.9995Capillary electrophoresis-based profiling and quantitation of total salicylic acid and related phenolics for analysis of early signaling in Arabidopsis disease resistance. A capillary electrophoresis-based method for quantitation of total salicylic acid levels in Arabidopsis leaves was developed. Direct comparison to previous high-performance liquid chromatography (HPLC)-based measurements showed similar levels of salicylic acid. Simultaneous quantitation of trans-cinnamic acid, benzoic acid, sinapic acid, and an internal recovery standard was achieved. A rapid, streamlined protocol with requirements for plant tissue reduced relative to those of HPLC-based protocols is presented. Complicated, multiparameter experiments were thus possible despite the labor-intensive nature of inoculating plants with bacterial pathogens. As an example of this sort of experiment, detailed time course studies of total salicylic acid accumulation by wild-type Arabidopsis and two lines with mutations affecting salicylic acid accumulation in response to either of two avirulent bacterial strains were performed. Accumulation in the first 12h was biphasic. The first phase was partially SID2 and NDR1 dependent with both bacterial strains. The second phase was largely independent of both genes with bacteria carrying avrB, but dependent upon both genes with bacteria carrying avrRpt2. Virulent bacteria did not elicit salicylic acid accumulation at these time points. Application of this method to various Arabidopsis pathosystems and the wealth of available disease resistance signaling mutants will refine knowledge of disease resistance and associated signal transduction.200312927828
814660.9995The Influence of Chitosan Derivatives in Combination with Bacillus subtilis Bacteria on the Development of Systemic Resistance in Potato Plants with Viral Infection and Drought. Viral diseases of potatoes are among the main problems causing deterioration in the quality of tubers and loss of yield. The growth and development of potato plants largely depend on soil moisture. Prevention strategies require comprehensive protection against pathogens and abiotic stresses, including modeling the beneficial microbiome of agroecosystems combining microorganisms and immunostimulants. Chitosan and its derivatives have great potential for use in agricultural engineering due to their ability to induce plant immune responses. The effect of chitosan conjugate with caffeic acid (ChCA) in combination with Bacillus subtilis 47 on the transcriptional activity of PR protein genes and changes in the proteome of potato plants during potato virus Y (PVY) infection and drought was studied. The mechanisms of increasing the resistance of potato plants to PVY and lack of moisture are associated with the activation of transcription of genes encoding PR proteins: the main protective protein (PR-1), chitinase (PR-3), thaumatin-like protein (PR-5), protease inhibitor (PR-6), peroxidase (PR-9), and ribonuclease (PR-10), as well as qualitative and quantitative changes in the plant proteome. The revealed activation of the expression of marker genes of systemic acquired resistance and induced systemic resistance under the influence of combined treatment with B. subtilis and chitosan conjugate indicate that, in potato plants, the formation of resistance to viral infection in drought conditions proceeds synergistically. By two-dimensional electrophoresis of S. tuberosum leaf proteins followed by MALDI-TOF analysis, 10 proteins were identified, the content and composition of which differed depending on the experiment variant. In infected plants treated with ChCA, the synthesis of proteinaceous RNase P 1 and oxygen-evolving enhancer protein 2 was enhanced in conditions of normal humidity, and 20 kDa chaperonin and TMV resistance protein N-like was enhanced in conditions of lack of moisture. The virus coat proteins were detected, which intensively accumulated in the leaves of plants infected with potato Y-virus. ChCA treatment reduced the content of these proteins in the leaves, and in plants treated with ChCA in combination with Bacillus subtilis, viral proteins were not detected at all, both in conditions of normal humidity and lack of moisture, which suggests the promising use of chitosan derivatives in combination with B. subtilis bacteria in the regulation of plant resistance.202439204646
879470.9995The Enhancement of Potato (Solanum Tuberosum L. Cv. Odyssey) Resistance to Bacterial Soft Rot Disease Through Transformation of the Glyphosate-Resistant Gene from Dickeya Dadanti. OBJECTIVE: An efficient protocol was developed via the Agrobacterium-mediated transformation method with the plasmid, p485, harboring the aroA gene from the bacterial species Dickeya dadantii, to improve resistance to potato bacterial soft rot disease. The study aimed to investigate the relationship between glyphosate application and the enhancement of potatoes' resistance to two bacterial pathogens affecting the plants. MATERIALS AND METHODS: An optimal concentration of 1.8 mg.L(-1) of glyphosate was applied to transgenic potato varieties. The leaves of the Odyssey cultivar demonstrated resistance to two pathogenic strains, Pectobacterium atrosepticum 21A and D. dadantii ENA49. Polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR) validation demonstrated the successful integration and heterologous expression of the aroA gene in the potato genome. Additionally, the transcriptional analysis revealed the expression of pathogenesis-related genes and genes associated with the potato defence response. RESULTS: The study revealed a significant increase in the expression of pathogenesis-related genes (PR-2, PR-3, and PR-5) and defence response genes (HSR-203j and HIN1 in transgenic potato leaves after glyphosate treatment and subsequent exposure to pathogenic bacterial infection, with a particular emphasis on the upregulation of HSR-203j. A comparative analysis assessed the average expression levels of these genes in both experimental and control samples. In contrast, minimal changes in gene expression were observed in plants infected with bacteria but not treated with glyphosate. CONCLUSION: The study suggests that glyphosate treatment in potatoes can enhance systemic acquired resistance to bacterial pathogens by upregulating pathogenesis-related and defence response genes. This approach shows potential for addressing bacterial diseases in potatoes, including soft bacterial rot.202440225297
877580.9995Induction of systemic resistance in tomato by N-acyl-L-homoserine lactone-producing rhizosphere bacteria. N-acyl-L-homoserine lactone (AHL) signal molecules are utilized by Gram-negative bacteria to monitor their population density (quorum sensing) and to regulate gene expression in a density-dependent manner. We show that Serratia liquefaciens MG1 and Pseudomonas putida IsoF colonize tomato roots, produce AHL in the rhizosphere and increase systemic resistance of tomato plants against the fungal leaf pathogen, Alternaria alternata. The AHL-negative mutant S. liquefaciens MG44 was less effective in reducing symptoms and A. alternata growth as compared to the wild type. Salicylic acid (SA) levels were increased in leaves when AHL-producing bacteria colonized the rhizosphere. No effects were observed when isogenic AHL-negative mutant derivatives were used in these experiments. Furthermore, macroarray and Northern blot analysis revealed that AHL molecules systemically induce SA- and ethylene-dependent defence genes (i.e. PR1a, 26 kDa acidic and 30 kDa basic chitinase). Together, these data support the view that AHL molecules play a role in the biocontrol activity of rhizobacteria through the induction of systemic resistance to pathogens.200617087474
8490.9995Two pathways act in an additive rather than obligatorily synergistic fashion to induce systemic acquired resistance and PR gene expression. BACKGROUND: Local infection with necrotizing pathogens induces whole plant immunity to secondary challenge. Pathogenesis-related genes are induced in parallel with this systemic acquired resistance response and thought to be co-regulated. The hypothesis of co-regulation has been challenged by induction of Arabidopsis PR-1 but not systemic acquired resistance in npr1 mutant plants responding to Pseudomonas syringae carrying the avirulence gene avrRpt2. However, experiments with ndr1 mutant plants have revealed major differences between avirulence genes. The ndr1-1 mutation prevents hypersensitive cell death, systemic acquired resistance and PR-1 induction elicited by bacteria carrying avrRpt2. This mutation does not prevent these responses to bacteria carrying avrB. RESULTS: Systemic acquired resistance, PR-1 induction and PR-5 induction were assessed in comparisons of npr1-2 and ndr1-1 mutant plants, double mutant plants, and wild-type plants. Systemic acquired resistance was displayed by all four plant lines in response to Pseudomonas syringae bacteria carrying avrB. PR-1 induction was partially impaired by either single mutation in response to either bacterial strain, but only fully impaired in the double mutant in response to avrRpt2. PR-5 induction was not fully impaired in any of the mutants in response to either avirulence gene. CONCLUSION: Two pathways act additively, rather than in an obligatorily synergistic fashion, to induce systemic acquired resistance, PR-1 and PR-5. One of these pathways is NPR1-independent and depends on signals associated with hypersensitive cell death. The other pathway is dependent on salicylic acid accumulation and acts through NPR1. At least two other pathways also contribute additively to PR-5 induction.200212381270
8788100.9995Plant nitrate supply regulates Erwinia amylovora virulence gene expression in Arabidopsis. We showed previously that nitrogen (N) limitation decreases Arabidopsis resistance to Erwinia amylovora (Ea). We show that decreased resistance to bacteria in low N is correlated with lower apoplastic reactive oxygen species (ROS) accumulation and lower jasmonic acid (JA) pathway expression. Consistently, pretreatment with methyl jasmonate (Me-JA) increased the resistance of plants grown under low N. In parallel, we show that in planta titres of a nonvirulent type III secretion system (T3SS)-deficient Ea mutant were lower than those of wildtype Ea in low N, as expected, but surprisingly not in high N. This lack of difference in high N was consistent with the low expression of the T3SS-encoding hrp virulence genes by wildtype Ea in plants grown in high N compared to plants grown in low N. This suggests that expressing its virulence factors in planta could be a major limiting factor for Ea in the nonhost Arabidopsis. To test this hypothesis, we preincubated Ea in an inducing medium that triggers expression of hrp genes in vitro, prior to inoculation. This preincubation strongly enhanced Ea titres in planta, independently of the plant N status, and was correlated to a significant repression of JA-dependent genes. Finally, we identify two clusters of metabolites associated with resistance or with susceptibility to Ea. Altogether, our data showed that high susceptibility of Arabidopsis to Ea, under low N or following preincubation in hrp-inducing medium, is correlated with high expression of the Ea hrp genes in planta and low expression of the JA signalling pathway, and is correlated with the accumulation of specific metabolites.202134382308
80110.9995Virus infection induces resistance to Pseudomonas syringae and to drought in both compatible and incompatible bacteria-host interactions, which are compromised under conditions of elevated temperature and CO(2) levels. Plants are simultaneously exposed to a variety of biotic and abiotic stresses, such as infections by viruses and bacteria, or drought. This study aimed to improve our understanding of interactions between viral and bacterial pathogens and the environment in the incompatible host Nicotiana benthamiana and the susceptible host Arabidopsis thaliana, and the contribution of viral virulence proteins to these responses. Infection by the Potato virus X (PVX)/Plum pox virus (PPV) pathosystem induced resistance to Pseudomonas syringae (Pst) and to drought in both compatible and incompatible bacteria-host interactions, once a threshold level of defence responses was triggered by the virulence proteins P25 of PVX and the helper component proteinase of PPV. Virus-induced resistance to Pst was compromised in salicylic acid and jasmonic acid signalling-deficient Arabidopsis but not in N. benthamiana lines. Elevated temperature and CO(2) levels, parameters associated with climate change, negatively affected resistance to Pst and to drought induced by virus infection, and this correlated with diminished H(2)O(2) production, decreased expression of defence genes and a drop in virus titres. Thus, diminished virulence should be considered as a potential factor limiting the outcome of beneficial trade-offs in the response of virus-infected plants to drought or bacterial pathogens under a climate change scenario.202031730035
323120.9994Systemic acquired resistance delays race shifts to major resistance genes in bell pepper. ABSTRACT The lack of durability of host plant disease resistance is a major problem in disease control. Genotype-specific resistance that involves major resistance (R) genes is especially prone to failure. The compatible (i.e., disease) host-pathogen interaction with systemic acquired resistance (SAR) has been studied extensively, but the incompatible (i.e., resistant) interaction less so. Using the pepper-bacterial spot (causal agent, Xanthomonas axonopodis pv. vesicatoria) pathosystem, we examined the effect of SAR in reducing the occurrence of race-change mutants that defeat R genes in laboratory, greenhouse, and field experiments. Pepper plants carrying one or more R genes were sprayed with the plant defense activator acibenzolar-S-methyl (ASM) and challenged with incompatible strains of the pathogen. In the greenhouse, disease lesions first were observed 3 weeks after inoculation. ASM-treated plants carrying a major R gene had significantly fewer lesions caused by both the incompatible (i.e., hypersensitive) and compatible (i.e., disease) responses than occurred on nonsprayed plants. Bacteria isolated from the disease lesions were confirmed to be race-change mutants. In field experiments, there was a delay in the detection of race-change mutants and a reduction in disease severity. Decreased disease severity was associated with a reduction in the number of race-change mutants and the suppression of disease caused by the race-change mutants. This suggests a possible mechanism related to a decrease in the pathogen population size, which subsequently reduces the number of race-change mutants for the selection pressure of R genes. Thus, inducers of SAR are potentially useful for increasing the durability of genotype-specific resistance conferred by major R genes.200418943709
8777130.9994Systemic resistance in Arabidopsis induced by biocontrol bacteria is independent of salicylic acid accumulation and pathogenesis-related gene expression. Systemic acquired resistance is a pathogen-inducible defense mechanism in plants. The resistant state is dependent on endogenous accumulation of salicylic acid (SA) and is characterized by the activation of genes encoding pathogenesis-related (PR) proteins. Recently, selected nonpathogenic, root-colonizing biocontrol bacteria have been shown to trigger a systemic resistance response as well. To study the molecular basis underlying this type of systemic resistance, we developed an Arabidopsis-based model system using Fusarium oxysporum f sp raphani and Pseudomonas syringae pv tomato as challenging pathogens. Colonization of the rhizosphere by the biological control strain WCS417r of P. fluorescens resulted in a plant-mediated resistance response that significantly reduced symptoms elicited by both challenging pathogens. Moreover, growth of P. syringae in infected leaves was strongly inhibited in P. fluorescens WCS417r-treated plants. Transgenic Arabidopsis NahG plants, unable to accumulate SA, and wild-type plants were equally responsive to P. fluorescens WCS417r-mediated induction of resistance. Furthermore, P. fluorescens WCS417r-mediated systemic resistance did not coincide with the accumulation of PR mRNAs before challenge inoculation. These results indicate that P. fluorescens WCS417r induces a pathway different from the one that controls classic systemic acquired resistance and that this pathway leads to a form of systemic resistance independent of SA accumulation and PR gene expression.19968776893
322140.9994Resistance inducers modulate Pseudomonas syringae pv. tomato strain DC3000 response in tomato plants. The efficacy of hexanoic acid (Hx) as an inducer of resistance in tomato plants against Pseudomonas syringae pv. tomato DC3000 was previously demonstrated, and the plant response was characterized. Because little is known about the reaction of the pathogen to this effect, the goal of the present work was to determine whether the changes in the plant defence system affect the pathogen behaviour. This work provides the first demonstration of the response of the pathogen to the changes observed in plants after Hx application in terms of not only the population size but also the transcriptional levels of genes involved in quorum sensing establishment and pathogenesis. Therefore, it is possible that Hx treatment attenuates the virulence and survival of bacteria by preventing or diminishing the appearance of symptoms and controlling the growth of the bacteria in the mesophyll. It is interesting to note that the gene transcriptional changes in the bacteria from the treated plants occur at the same time as the changes in the plants. Hx is able to alter bacteria pathogenesis and survival only when it is applied as a resistance inducer because the changes that it promotes in plants affect the bacteria.201425244125
8786150.9994Pattern triggered immunity (PTI) in tobacco: isolation of activated genes suggests role of the phenylpropanoid pathway in inhibition of bacterial pathogens. BACKGROUND: Pattern Triggered Immunity (PTI) or Basal Resistance (BR) is a potent, symptomless form of plant resistance. Upon inoculation of a plant with non-pathogens or pathogenicity-mutant bacteria, the induced PTI will prevent bacterial proliferation. Developed PTI is also able to protect the plant from disease or HR (Hypersensitive Response) after a challenging infection with pathogenic bacteria. Our aim was to reveal those PTI-related genes of tobacco (Nicotiana tabacum) that could possibly play a role in the protection of the plant from disease. METHODOLOGY/PRINCIPAL FINDINGS: Leaves were infiltrated with Pseudomonas syringae pv. syringae hrcC- mutant bacteria to induce PTI, and samples were taken 6 and 48 hours later. Subtraction Suppressive Hybridization (SSH) resulted in 156 PTI-activated genes. A cDNA microarray was generated from the SSH clone library. Analysis of hybridization data showed that in the early (6 hpi) phase of PTI, among others, genes of peroxidases, signalling elements, heat shock proteins and secondary metabolites were upregulated, while at the late phase (48 hpi) the group of proteolysis genes was newly activated. Microarray data were verified by real time RT-PCR analysis. Almost all members of the phenyl-propanoid pathway (PPP) possibly leading to lignin biosynthesis were activated. Specific inhibition of cinnamic-acid-4-hydroxylase (C4H), rate limiting enzyme of the PPP, decreased the strength of PTI--as shown by the HR-inhibition and electrolyte leakage tests. Quantification of cinnamate and p-coumarate by thin-layer chromatography (TLC)-densitometry supported specific changes in the levels of these metabolites upon elicitation of PTI. CONCLUSIONS/SIGNIFICANCE: We believe to provide first report on PTI-related changes in the levels of these PPP metabolites. Results implicated an actual role of the upregulation of the phenylpropanoid pathway in the inhibition of bacterial pathogenic activity during PTI.201425101956
81160.9994Biological control of bacterial wilt in Arabidopsis thaliana involves abscissic acid signalling. Means to control bacterial wilt caused by the phytopathogenic root bacteria Ralstonia solanacearum are limited. Mutants in a large cluster of genes (hrp) involved in the pathogenicity of R. solanacearum were successfully used in a previous study as endophytic biocontrol agents in challenge inoculation experiments on tomato. However, the molecular mechanisms controlling this resistance remained unknown. We developed a protection assay using Arabidopsis thaliana as a model plant and analyzed the events underlying the biological control by genetic, transcriptomic and molecular approaches. High protection rates associated with a significant decrease in the multiplication of R. solanacearum were observed in plants pre-inoculated with a ΔhrpB mutant strain. Neither salicylic acid, nor jasmonic acid/ethylene played a role in the establishment of this resistance. Microarray analysis showed that 26% of the up-regulated genes in protected plants are involved in the biosynthesis and signalling of abscissic acid (ABA). In addition 21% of these genes are constitutively expressed in the irregular xylem cellulose synthase mutants (irx), which present a high level of resistance to R. solanacearum. We propose that inoculation with the ΔhrpB mutant strain generates a hostile environment for subsequent plant colonization by a virulent strain of R. solanacearum.201222432714
79170.9994A novel link between tomato GRAS genes, plant disease resistance and mechanical stress response. SUMMARY Members of the GRAS family of transcriptional regulators have been implicated in the control of plant growth and development, and in the interaction of plants with symbiotic bacteria. Here we examine the complexity of the GRAS gene family in tomato (Solanum lycopersicum) and investigate its role in disease resistance and mechanical stress. A large number of tomato ESTs corresponding to GRAS transcripts were retrieved from the public database and assembled in 17 contigs of putative genes. Expression analysis of these genes by real-time RT-PCR revealed that six SlGRAS transcripts accumulate during the onset of disease resistance to Pseudomonas syringae pv. tomato. Further analysis of two selected family members showed that their transcripts preferentially accumulate in tomato plants in response to different avirulent bacteria or to the fungal elicitor EIX, and their expression kinetics correlate with the appearance of the hypersensitive response. In addition, transcript levels of eight SlGRAS genes, including all the Pseudomonas-inducible family members, increased in response to mechanical stress much earlier than upon pathogen attack. Accumulation of SlGRAS transcripts following mechanical stress was in part dependent on the signalling molecule jasmonic acid. Remarkably, suppression of SlGRAS6 gene expression by virus-induced gene silencing impaired tomato resistance to P. syringae pv. tomato. These results support a function for GRAS transcriptional regulators in the plant response to biotic and abiotic stress.200620507472
8149180.9994Genes related to antioxidant metabolism are involved in Methylobacterium mesophilicum-soybean interaction. The genus Methylobacterium is composed of pink-pigmented methylotrophic bacterial species that are widespread in natural environments, such as soils, stream water and plants. When in association with plants, this genus colonizes the host plant epiphytically and/or endophytically. This association is known to promote plant growth, induce plant systemic resistance and inhibit plant infection by phytopathogens. In the present study, we focused on evaluating the colonization of soybean seedling-roots by Methylobacterium mesophilicum strain SR1.6/6. We focused on the identification of the key genes involved in the initial step of soybean colonization by methylotrophic bacteria, which includes the plant exudate recognition and adaptation by planktonic bacteria. Visualization by scanning electron microscopy revealed that M. mesophilicum SR1.6/6 colonizes soybean roots surface effectively at 48 h after inoculation, suggesting a mechanism for root recognition and adaptation before this period. The colonization proceeds by the development of a mature biofilm on roots at 96 h after inoculation. Transcriptomic analysis of the planktonic bacteria (with plant) revealed the expression of several genes involved in membrane transport, thus confirming an initial metabolic activation of bacterial responses when in the presence of plant root exudates. Moreover, antioxidant genes were mostly expressed during the interaction with the plant exudates. Further evaluation of stress- and methylotrophic-related genes expression by qPCR showed that glutathione peroxidase and glutathione synthetase genes were up-regulated during the Methylobacterium-soybean interaction. These findings support that glutathione (GSH) is potentially a key molecule involved in cellular detoxification during plant root colonization. In addition to methylotrophic metabolism, antioxidant genes, mainly glutathione-related genes, play a key role during soybean exudate recognition and adaptation, the first step in bacterial colonization.201526238382
8778190.9994The transcriptome of rhizobacteria-induced systemic resistance in arabidopsis. Plants develop an enhanced defensive capacity against a broad spectrum of plant pathogens after colonization of the roots by selected strains of nonpathogenic, fluorescent Pseudomonas spp. In Arabidopsis thaliana, this rhizobacteria-induced systemic resistance (ISR) functions independently of salicylic acid but requires responsiveness to the plant hormones jasmonic acid and ethylene. In contrast to pathogen-induced systemic acquired resistance, rhizobacteria-mediated ISR is not associated with changes in the expression of genes encoding pathogenesis-related proteins. To identify ISR-related genes, we surveyed the transcriptional response of over 8,000 Arabidopsis genes during rhizobacteria-mediated ISR. Locally in the roots, ISR-inducing Pseudomonas fluorescens WCS417r bacteria elicited a substantial change in the expression of 97 genes. However, systemically in the leaves, none of the approximately 8,000 genes tested showed a consistent change in expression in response to effective colonization of the roots by WCS417r, indicating that the onset of ISR in the leaves is not associated with detectable changes in gene expression. After challenge inoculation of WCS417r-induced plants with the bacterial leaf pathogen P. syringae pv. tomato DC3000, 81 genes showed an augmented expression pattern in ISR-expressing leaves, suggesting that these genes were primed to respond faster or more strongly upon pathogen attack. The majority of the primed genes was predicted to be regulated by jasmonic acid or ethylene signaling. Priming of pathogen-induced genes allows the plant to react more effectively to the invader encountered, which might explain the broad-spectrum action of rhizobacteria-mediated ISR.200415305611