Pathogenic Bacterium Ralstonia Solanacearum Research Articles

Isolation and identification of antifungal, antibacterial and nematocide agents from marine bacillus gottheilii MSB1.

Pathogenic fungi employ numerous strategies to colonize plants, infect them, reduce crop yield and quality, and cause significant losses in agricultural production. The increasing use of chemical pesticides has led to various ecological and environmental issues, including the emergence of resistant weeds, soil compaction, and water pollution, all negatively impacting agricultural sustainability. Additionally, the extensive development of synthetic fungicides has adverse effects on animal and human health, prompting the exploration of alternative approaches and green strategies for phytopathogen control. Microorganisms living in sponges represent a promising source of novel bioactive secondary metabolites, potentially useful in developing new nematicidal and antimicrobial agents. This study focuses on extracting bioactive compounds from endosymbiotic bacteria associated with the marine sponge Hyrtios erect sp. (collected from NIOF Station, Hurghada, Red Sea, Egypt) using various organic solvents. Bacillus sp. was isolated and identified through 16S rRNA gene sequencing. The biocidal activity of Bacillus gotheilii MSB1 extracts was screened against plant pathogenic bacteria, fungi, and nematodes. The n-butanol extract showed significant potential as a biological fungicide against Alternaria alternata and Fusarium oxysporum. Both n-hexane and ethyl acetate extracts exhibited negative impacts against the plant pathogenic bacteria Erwinia carotovora and Ralstonia solanacearum, whereas the n-butanol extract had a positive effect. Regarding nematicidal activity, ethyl acetate and n-butanol extracts demonstrated in-vitro activity against the root-knot nematode Meloidogyne incognita, which causes serious vegetable crop diseases, but the n-hexane extract showed no positive effects. The findings suggest that bioactive compounds from endosymbiotic bacteria associated with marine sponges, particularly B. gotheilii MSB1, hold significant potential as alternative biological control agents against plant pathogens. The n-butanol extract, in particular, displayed promising biocidal activities against various plant pathogenic fungi, bacteria, and nematodes. These results support further exploration and development of such bioactive compounds as sustainable, environmentally friendly alternatives to synthetic pesticides and fungicides in agricultural practices.

Antibacterial, Herbicidal, and Plant Growth-Promoting Properties of Streptomyces sp. STD57 from the Rhizosphere of Adenophora stricta

Bacterial wilt triggered by the soil-borne pathogenic bacterium Ralstonia solanacearum is one of the most serious diseases in tomato plants, leading to huge economic losses worldwide. Biological control is considered an environmentally friendly and sustainable way to manage soil-borne diseases. In this study, Streptomyces sp. STD57 isolated from the rhizosphere of Adenophora stricta showed strong antibacterial activity against R. solanacearum. Pot experiments showed that strain STD57 exhibited a significant biocontrol effect (81.7%) on tomato bacterial wilt in the greenhouse environment. Furthermore, strain STD57 could inhibit the growth of weeds (Amaranthus retroflexus, Portulaca oleracea, and Echinochloa crusgalli) but promote the growth of crops (wheat, rice, and tomato). The plant growth-promoting substance was identified as indoleacetic acid (IAA) by high-pressure liquid chromatography–mass spectrometry and genome analysis. Coarse separation of the fermented extracts revealed that the antibacterial and herbicidal substances were mainly in the fermentation supernatant and belonged to different products. These findings suggested that strain STD57 may be a potential biocontrol and bioherbicide agent useful in agriculture.

Parthenium hysterophorus alleviates wilt stress in tomato plants caused by Ralstonia solanacearum through direct antibacterial effect and indirect upregulation of host resistance.

Heavy damage to tomato crops due to wilt stress caused by the pathogenic bacterium Ralstonia solanacearum and the insufficient availability of management strategies with desired control levels urged the researchers to investigate more reliable control methods to manage this issue in tomato and other horticultural crops. In this study, Parthenium hysterophorus, a locally and freely available herbaceous plant, was successfully used to manage bacterial wilt of tomatoes. The significant growth reduction ability of P. hysterophorus leaf extract was recorded in an agar well diffusion test and its ability to severally damage the bacterial cells was confirmed in SEM analysis. In both greenhouse and field trials, soil amended with P. hysterophorus leaf powder at 25 g/kg soil was found to effectively suppress the pathogen population in soil and significantly reduce the wilt severity on tomato plants, resulting in increased growth and yield of tomato plants. P. hysterophorus leaf powder at concentrations greater than 25 g/kg soil caused phytotoxicity in tomato plants. The results showed that P. hysterophorus powder applied through the mixing of soil for a longer period of time before transplanting tomato plants was more effective than mulching application and a shorter period of transplantation. Finally, the indirect effect of P. hysterophorus powder in managing bacterial wilt stress was evaluated using expression analysis of two resistance-related genes, PR2 and TPX. The upregulation of these two resistance-related genes was recorded by the soil application of P. hysterophorus powder. The findings of this study revealed the direct and indirect action mechanisms of P. hysterophorus powder applied to the soil for the management of bacterial wilting stress in tomato plants and provided the basis for including this technique as a safe and effective management strategy in an integrated disease management package.

Resource availability drives bacteria community resistance to pathogen invasion via altering bacterial pairwise interactions.

Microbial interactions within resident communities are a major determinant of resistance to pathogen invasion. Yet, interactions vary with environmental conditions, raising the question of how community composition and environments interactively shape invasion resistance. Here, we use resource availability (RA) as a model parameter altering the resistance of model bacterial communities to invasion by the plant pathogenic bacterium Ralstonia solanacearum. We found that at high RA, interactions between resident bacterial species were mainly driven by the direct antagonism, in terms of the means of invader inhibition. Consequently, the competitive resident communities with a higher production of antibacterial were invaded to a lesser degree than facilitative communities. At low RA, bacteria produced little direct antagonist potential, but facilitative communities reached a relatively higher community productivity, which showed higher resistance to pathogen invasion than competitive communities with lower productivities. This framework may lay the basis to understand complex microbial interactions and biological invasion as modulated by the dynamic changes of environmental resource availability.

Maintenance of tRNA and elongation factors supports T3SS proteins translational elongations in pathogenic bacteria during nutrient starvation

BackgroundSufficient nutrition contributes to rapid translational elongation and protein synthesis in eukaryotic cells and prokaryotic bacteria. Fast synthesis and accumulation of type III secretion system (T3SS) proteins conduce to the invasion of pathogenic bacteria into the host cells. However, the translational elongation patterns of T3SS proteins in pathogenic bacteria under T3SS-inducing conditions remain unclear. Here, we report a mechanism of translational elongation of T3SS regulators, effectors and structural protein in four model pathogenic bacteria (Pseudomonas syringae, Pseudomonas aeruginosa, Xanthomonas oryzae and Ralstonia solanacearum) and a clinical isolate (Pseudomonas aeruginosa UCBPP-PA14) under nutrient-limiting conditions. We proposed a luminescence reporter system to quantitatively determine the translational elongation rates (ERs) of T3SS regulators, effectors and structural protein under different nutrient-limiting conditions and culture durations.ResultsThe translational ERs of T3SS regulators, effectors and structural protein in these pathogenic bacteria were negatively regulated by the nutrient concentration and culture duration. The translational ERs in 0.5× T3SS-inducing medium were the highest of all tested media. In 1× T3SS-inducing medium, the translational ERs were highest at 0 min and then rapidly decreased. The translational ERs of T3SS regulators, effectors and structural protein were inhibited by tRNA degradation and by reduced levels of elongation factors (EFs).ConclusionsRapid translational ER and synthesis of T3SS protein need adequate tRNAs and EFs in nutrient-limiting conditions. Numeric presentation of T3SS translation visually indicates the invasion of bacteria and provides new insights into T3SS expression that can be applied to other pathogenic bacteria.

Inactivation of plant pathogenic bacterium Ralstonia solanacearum in drainage solution from hydroponic system by a rotating advanced oxidation contactor equipped with TiO2/zeolite composite sheets

A rotating advanced oxidation contactor (RAOC) equipped with TiO2/zeolite composite sheets was developed to inactivate the plant pathogenic bacterium Ralstonia solanacearum in drainage solution (DS) from a hydroponic system. The inactivation efficiency of R. solanacearum in DS and pure culture solution (PS) by the RAOC was compared with that achieved by a submerged composite sheet photocatalysis reactor (SSPR). The initial number of living bacteria (N0) was adjusted to around 106–107 CFU mL−1. The inactivation efficiency of R. solanacearum by the SSPR at 4.0 × 107 CFU mL−1 of N0 significantly decreased compared with that at 1.8 × 106 CFU mL−1 of N0 owing to the attenuation of UV intensity by light absorption and scattering by solids derived from R. solanacearum, while the RAOC achieved >2-log inactivation during 24 h of treatment regardless of N0. The inactivation of R. solanacearum by the RAOC decelerated after 6 h, possibly because of competition for reactive oxygen species between R. solanacearum and products accumulated by inactivation of R. solanacearum. The ratio of rate constants for inactivation of R. solanacearum in DS to that in PS by the RAOC was 8 times that for the SSPR. This shows that the RAOC greatly mitigates the light attenuation and inhibitory effects of coexisting substances on inactivation of R. solanacearum in the DS. The RAOC is therefore a promising and upscalable photocatalytic reactor for efficient inactivation of R. solanacearum in DS.

Myxococcus xanthus R31 Suppresses Tomato Bacterial Wilt by Inhibiting the Pathogen Ralstonia solanacearum With Secreted Proteins.

The pathogenic bacterium Ralstonia solanacearum caused tomato bacterial wilt (TBW), a destructive soil-borne disease worldwide. There is an urgent need to develop effective control methods. Myxobacteria are microbial predators and are widely distributed in the soil. Compared with other biocontrol bacteria that produce antibacterial substances, the myxobacteria have great potential for biocontrol. This study reports a strain of Myxococcus xanthus R31 that exhibits high antagonistic activity to R. solanacearum. Plate test indicated that the strain R31 efficiently predated R. solanacearum. Pot experiments showed that the biocontrol efficacy of strain R31 against TBW was 81.9%. Further study found that the secreted protein precipitated by ammonium sulfate had significant lytic activity against R. solanacearum cells, whereas the ethyl acetate extract of strain R31 had no inhibitory activity against R. solanacearum. Substrate spectroscopy assay and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of secreted proteins showed that some peptidases, lipases, and glycoside hydrolases might play important roles and could be potential biocontrol factors involved in predation. The present study reveals for the first time that the use of strain M. xanthus R31 as a potential biocontrol agent could efficiently control TBW by predation and secreting extracellular lyase proteins.

Effect of Phyto‐Assisted Synthesis of Magnesium Oxide Nanoparticles (MgO‐NPs) on Bacteria and the Root‐Knot Nematode

The root-knot nematode was examined using magnesium oxide nanoparticles (MgO-NPs) made from strawberries. The biologically synthesized MgO-NPs were characterized by UV, SEM, FTIR, EDS, TEM, and dynamic light scattering (DLS). Nanoparticles (NPs) were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and shown to be spherical to hexagonal nanoparticles with an average size of 100 nm. MgO-NPs were tested on the root-knot nematode M. incognita (Meloidogynidae) and the plant pathogenic bacteria Ralstonia solanacearum. The synthesized MgO-NPs showed a significant inhibition of R. solanacearum and the root-knot nematode. MgO-NPs cause mortality and inhibit egg hatching of second-stage juveniles (J2) of M. incognita under the in vitro assay. This study aims to examine the biological activity of biogenic MgO-NPs. The findings marked that MgO-NPs may be utilized to manage R. solanacearum and M. incognita and develop effective nematicides. In addition, the antioxidant capacity of MgO-NPs was determined by using 2, 2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH).

English

Bacterial wilt is a serious disease of potato (Solanum tuberosum L.) caused by the soil-borne pathogenic bacterium Ralstonia solanacearum. Detecting changes in protein abundance in potato plants in response to R. solanacearum is a pivotal step in uncovering the molecular interactions of plant pathogens. In this study, using the disease-resistant cultivar ‘Zhongshu 3’, we analyzed protein expression in potato seedlings inoculated with R. solanacearum every 12 h for a total of 72 h using isobaric tags for relative and absolute quantitation-based proteomics. Our results indicate that pathogenesis-related proteins, stressrelated proteins, non-specific lipid transfer proteins, small heat shock proteins, and osmotin-like proteins were up-regulated in response to pathogen infection at different time points. The accumulation of these proteins in response to biotic stress suggests that these proteins play an important role in pathogen resistance. Our findings will provide an important basis for characterizing the role of these proteins in increasing plant resistance to pathogens and in breeding bacterial wilt-resistant plants.

Inactivation of Plant Pathogenic Bacterium Ralstonia Solanacearum in Drainage Solution from Hydroponic System by a Rotating Advanced Oxidation Contactor Equipped with Tio2/Zeolite Composite Sheets

Inactivation of Plant Pathogenic Bacterium Ralstonia Solanacearum in Drainage Solution from Hydroponic System by a Rotating Advanced Oxidation Contactor Equipped with Tio2/Zeolite Composite Sheets

Antimicrobial and Antioxidant properties of medicinal mushroom Ganoderma P. Karst

Ganoderma species have been known all over the world as highly medicinal mushrooms. Antimicrobial activity of it is an attractive approach which raises the global interests from the scientific community. In this study, the antimicrobial assay of ethanol and methanol extracts of Ganoderma were prepared by using the dried mycelial powder obtained from five different liquid media; was performed against seven plant pathogenic fungi viz., Alternaria macrospora, Aspergilus niger, A. flavus, Colletotrichum falcatum, Fusarium oxysporum, Pestalotiopsis mangiferae and Penicillium sp. and two plant pathogenic bacteria Xanthomonas oryzae and Ralstonia solanacearum. The extracts of mycelia obtained from Yeast Wine Media exhibited the highest inhibition percentage as compared to rest. At concentration 1000ppm, there was complete inhibition of mycelial growth for Alternaria macrospora, Aspergilus niger and A. flavus while for Fusarium oxysporum and Penicillum sp. complete inhibition was observed at 500ppm but for Colletotrichum falcatum and Pestalotiopsis mangiferae, more than 80% mycelial inhibition at concentration 1000ppm in both ethanol and methanol extracts. In the case of Xanthomonas oryzae and Ralstonia solanacearum, at concentration 1000ppm, methanol extract showed the highest inhibition zone (3.50mm, 3.75mm). Ganoderma exhibited antagonistic effect against plant pathogenic fungi could add to the interest of developing Ganoderma as a successful bioagent in the near future. Antioxidant activities were evaluated by using DPPH radical scavenging assay and Metal chelating activity on ferrous ions. The DPPH radical scavenging effect was detected in methanol extract (Inhibition% = 27.312%) was higher than that of the ethanol extract (Inhibition% = 24.79%) and also Ferrous ion chelating ability of methanol extract (Inhibition% =22.27%) was higher than the ethanol extract (Inhibition% =12.55%). It is clearly indicated that both methanol and ethanol extract of the Ganoderma show antioxidant properties and Ganoderma extracts act as an effective antioxidant agents.

Effects of Combined Application of Potassium Silicate and Salicylic Acid on the Defense Response of Hydroponically Grown Tomato Plants to Ralstonia solanacearum Infection

Bacterial wilt, caused by soilborne pathogenic bacterium Ralstonia solanacearum, is a serious and widespread disease that affects global tomato production. Both silicon (Si) and salicylic acid (SA) play important roles in enhancing tomato resistance against bacterial wilt, however, their combined effects on the defense responses of infected tomato plants remain unknown. Hence, the combined effects of Si and SA on physiological and biochemical parameters of R. solanacearum-infected tomato plants were investigated. The combination treatment of Si and SA significantly decreased disease incidences, lipoxygenase (LOX) activity and ethylene (ET) production. The combined treatments were more prominent in improving the morphological traits of root systems, such as root length, root surface area, average root diameter and root volume. The activities of polyphenol oxidase (PPO) and peroxidase (POD) and the concentrations of total soluble phenolics (TSPs) and lignin-thioglycolic acid (LTGA) derivatives were significantly increased in the plants with combined treatments. Si in combination with SA could significantly enhance neutral invertase (NI) and acid invertases (AI) activities in the leaves of tomato plants at 3 days post-infection (dpi) compared with application of Si alone. Three defense-related genes, PAL, POD and pathogenesis-related protein 1 (PR1), were significantly induced in Si+SA treatment at 7 dpi when compared with individual application of Si or SA. The expression level of salicylic acid-binding protein 2 (SABP2) was significantly higher for combination treatment when compared with treatment of Si or SA alone. The possible mechanisms involved in the synergistic effects of Si and SA on the control of tomato bacterial wilt were proposed. This study indicates that under hypertonic conditions, the combined application of 2.0 mM potassium silicate (K2SiO3) and 0.5 mM SA had a synergistic effect on the control of tomato bacterial wilt.

CaWRKY28 Cys249 is Required for Interaction with CaWRKY40 in the Regulation of Pepper Immunity to Ralstonia solanacearum.

WRKY transcription factors have been implicated in plant response to pathogens but how WRKY-mediated networks are organized and operate to produce appropriate transcriptional outputs remains largely unclear. Here, we identify a member of the WRKY family from pepper (Capsicum annuum), CaWRKY28, that physically interacts with CaWRKY40, a positive regulator of pepper immunity and thermotolerance. We confirmed CaWRKY28-CaWRKY40 interaction by coimmunoprecipitation, bimolecular fluorescence complementation, and microscale thermophoresis. Our findings supported the idea that CaWRKY28 is a nuclear protein that acts as positive regulator in pepper responses to infection by the pathogenic bacterium Ralstonia solanacearum. It performs its function not by directly modulating the W-box containing immunity-related genes but by promoting CaWRKY40 via physical interaction to bind and activate its immunity-related target genes, including CaPR1, CaNPR1, CaDEF1, and CaABR1, but not its thermotolerance-related target gene, CaHSP24. All of these data indicate that CaWRKY28 interacts with and potentiates CaWRKY40 in regulating immunity against R. solanacearum infection but not thermotolerance. Importantly, we discovered that CaWRKY28 Cys249, shared by CaWRKY28 and its orthologs probably only in the family Solanaceae, is crucial for the CaWRKY28-CaWRKY40 interaction. These results highlight how CaWRKY28 associates with CaWRKY40 during the establishment of WRKY networks, and how CaWRKY40 achieves its functional specificity during pepper responses to R. solanacearum infection.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Bacterial ClpP Protease Is a Potential Target for Methyl Gallate.

Methyl gallate (MG) is an effective microbicide with great potential application in the integrated management of plant diseases and an important potential drug for clinical application. However, its target remains unknown. This study conducted a transposon sequencing (Tn-seq) under MG treatment in plant pathogenic bacterium Ralstonia solanacearum. Tn-seq identified that the mutation of caseinolytic protease proteolytic subunit gene clpP significantly increased the resistance of R. solanacearum to MG, which was validated by the in-frame gene deletion. iTRAQ (isobaric tags for relative and absolute quantitation) proteomics analysis revealed that chemotaxis and flagella associated proteins were the major substrates degraded by ClpP under the tested condition. Moreover, sulfur metabolism-associated proteins were potential substrates of ClpP and were upregulated by MG treatment in wild-type R. solanacearum but not in clpP mutant. Furthermore, molecular docking confirmed the possible interaction between MG and ClpP. Collectively, this study revealed that MG might target bacterial ClpP, inhibit the activity of ClpP, and consequently disturb bacterial proteostasis, providing a theoretical basis for the application of MG.

Insights into the Root Invasion by the Plant Pathogenic Bacterium Ralstonia solanacearum.

The plant pathogenic bacterium Ralstonia solanacearum, causal agent of the devastating bacterial wilt disease, is a soil-borne microbe that infects host plants through their roots. The initial mutual recognition between host plants and bacteria and the ensuing invasion of root tissues by R. solanacearum are critical steps in the establishment of the infection, and can determine the outcome of the interaction between plant and pathogen. In this minireview, we will focus on the early stages of the bacterial invasion, offering an overview of the defence mechanisms deployed by the host plants, the manipulation exerted by the pathogen in order to promote virulence, and the alterations in root development concomitant to bacterial colonization.

Medicago-Sinorhizobium-Ralstonia Co-infection Reveals Legume Nodules as Pathogen Confined Infection Sites Developing Weak Defenses.

Legumes have the capacity to develop root nodules hosting nitrogen-fixing bacteria, called rhizobia. For the plant, the benefit of the symbiosis is important in nitrogen-deprived conditions, but it requires hosting and feeding massive numbers of rhizobia. Recent studies suggest that innate immunity is reduced or suppressed within nodules [1-10]; this likely maintains viable rhizobial populations. To evaluate the potential consequences and risks associated with an altered immuni`ty in the symbiotic organ, we developed a tripartite system with the model legume Medicago truncatula [11, 12], its nodulating symbiont of the genus Sinorhizobium (syn. Ensifer) [13, 14], and the pathogenic soil-borne bacterium Ralstonia solanacearum [15-18]. We show that nodules are frequent infection sites where pathogen multiplication is comparable to that in the root tips and independent of nodule ability to fix nitrogen. Transcriptomic analyses indicate that, despite the presence of the hosted rhizobia, nodules are able to develop weak defense reactions against pathogenic R.solanacearum. Nodule defense response displays specificity compared to that activated in roots. In agreement with nodule innate immunity, optimal R.solanacearum growth requires pathogen virulence factors. Finally, our data indicate that the high susceptibility of nodules is counterbalanced by the existence of a diffusion barrier preventing pathogen spreading from nodules to the rest of the plant.

CaWRKY27 negatively regulates salt and osmotic stress responses in pepper

WRKY transcription factors are key regulatory components of plant responses to both biotic and abiotic stresses. In pepper (Capsicum annuum), CaWRKY27 positively regulates resistance to the pathogenic bacterium Ralstonia solanacearum and negatively regulates thermotolerance. Here, we report that CaWRKY27 functions in the response to salinity and osmotic stress. CaWRKY27 transcription was induced by salinity, osmotic, and abscisic acid (ABA) treatments, as determined using qPCR and GUS assays. Transgenic Arabidopsis thaliana and tobacco (Nicotiana tabacum) plants heterologously expressing CaWRKY27 had an increased sensitivity to salinity and osmotic stress, with a higher inhibition of both root elongation and whole plant growth, more severe chlorosis and wilting, lower germination rates, and an enhanced germination sensitivity to ABA than the corresponding wild-type plants. Furthermore, most marker genes associated with reactive oxygen species (ROS) detoxification and polyamine and ABA biosynthesis, as well as stress-responsive genes NtDREB3, were downregulated in plants transgenically expressing CaWRKY27 upon exposure to salinity or osmotic stress. Consistently, silencing of CaWRKY27 using virus-induced gene silencing conferred tolerance to salinity and osmotic stress in pepper plants. These findings suggest that CaWRKY27 acts as a molecular link in the antagonistic crosstalk regulating the expression of defense-related genes in the responses to both abiotic and biotic stresses by acting either as a transcriptional activator or repressor in pepper.

Effect of Different Concentrations of Ozone on in Vitro Plant Pathogens Development, Tomato Yield and Quality, Photosynthetic Activity and Enzymatic Activities

ABSTRACTAs an effective alternative to traditional pesticides, ozonated water has been used for direct immersion and spraying applications, respectively, against the pathogenic bacterium Ralstonia solanacearum (R. solanacearum) and fungus Alternaria solani (A. solani) that are pathogens of tomato. Immersing R. solanacearum in 0.8 mg/L ozonated water resulted in complete inactivation, while the growth-inhibition rates of the A. solani radial mycelia gradually increased with a 67.0% decrease compared to those of the control at an ozonated water concentration of 7.5 mg/L. This indicated that ozonated water was effective at restraining pathogens in the tomato plant. In addition, spraying wild tomato species (Solanum lycopersicum) plants with ozonated water at concentrations below 10 mg/L for 25 d had no negative effects after treatment compared to those of the control. Photosynthetic activities and the antioxidant system response in the untreated and ozonated water-treated plant leaves had no observable changes. To determine the optimal ozonated water concentration for the pathogen and its host plant, we examined a variety of modes of action, and then, below 10 mg/L of ozonated water. Thus, ozonated water not only inhibits the proliferation of plant pathogens, but is an effective alternative to the pesticides traditionally used to prevent disease in agricultural production.

Transcriptome Analysis Reveals New Insights into the Bacterial Wilt Resistance Mechanism Mediated by Silicon in Tomato.

Bacterial wilt is a devastating disease of tomato caused by soilborne pathogenic bacterium Ralstonia solanacearum. Previous studies found that silicon (Si) can increase tomato resistance against R. solanacearum, but the exact molecular mechanism remains unclear. RNA sequencing (RNA-Seq) technology was used to investigate the dynamic changes of root transcriptome profiles between Si-treated (+Si) and untreated (−Si) tomato plants at 1, 3, and 7 days post-inoculation with R. solanacearum. The contents of salicylic acid (SA), ethylene (ET), and jasmonic acid (JA) and the activity of defense-related enzymes in roots of tomato in different treatments were also determined. The burst of ET production in roots was delayed, and SA and JA contents were altered in Si treatment. The transcriptional response to R. solanacearum infection of the +Si plants was quicker than that of the untreated plants. The expression levels of differentially-expressed genes involved in pathogen-associated molecular pattern-triggered immunity (PTI), oxidation resistance, and water-deficit stress tolerance were upregulated in the Si-treated plants. Multiple hormone-related genes were differentially expressed in the Si-treated plants. Si-mediated resistance involves mechanisms other than SA- and JA/ET-mediated stress responses. We propose that Si-mediated tomato resistance to R. solanacearum is associated with activated PTI-related responses and enhanced disease resistance and tolerance via several signaling pathways. Such pathways are mediated by multiple hormones (e.g., SA, JA, ET, and auxin), leading to diminished adverse effects (e.g., senescence, water-deficit, salinity and oxidative stress) normally caused by R. solanacearum infection. This finding will provide an important basis to further characterize the role of Si in enhancing plant resistance against biotic stress.

A feedback loop between CaWRKY41 and H2O2 coordinates the response to Ralstonia solanacearum and excess cadmium in pepper.

WRKY transcription factors have been implicated in both plant immunity and plant responses to cadmium (Cd); however, the mechanism underlying the crosstalk between these processes is unclear. Here, we characterized the roles of CaWRKY41, a group III WRKY transcription factor, in immunity against the pathogenic bacterium Ralstonia solanacearum and Cd stress responses in pepper (Capsicum annuum). CaWRKY41 was transcriptionally up-regulated in response to Cd exposure, R. solanacearum inoculation, and H2O2 treatment. Virus-induced silencing of CaWRKY41 increased Cd tolerance and R. solanacearum susceptibility, while heterologous overexpression of CaWRKY41 in Arabidopsis impaired Cd tolerance, and enhanced Cd and zinc (Zn) uptake and H2O2 accumulation. Genes encoding reactive oxygen species-scavenging enzymes were down-regulated in CaWRKY41-overexpressing Arabidopsis plants, whereas genes encoding Zn transporters and enzymes involved in H2O2 production were up-regulated. Consistent with these findings, the ocp3 (overexpressor of cationic peroxidase 3) mutant, which has elevated H2O2 levels, displayed enhanced sensitivity to Cd stress. These results suggest that a positive feedback loop between H2O2 accumulation and CaWRKY41 up-regulation coordinates the responses of pepper to R. solanacearum inoculation and Cd exposure. This mechanism might reduce Cd tolerance by increasing Cd uptake via Zn transporters, while enhancing resistance to R. solanacearum.