Solanum lycopersicum heme-binding protein 2 as a potent antimicrobial weapon against plant pathogens.

The rise in antibiotic-resistant bacteria caused by the excessive use of antibiotics has led to the urgent exploration of alternative antimicrobial solutions. Among these alternatives, antimicrobial proteins, and peptides (Apps) have garnered attention due to their wide-ranging antimicrobial effects. This study focuses on evaluating the antimicrobial properties of Solanum lycopersicum heme-binding protein 2 (SlHBP2), an apoplastic protein extracted from tomato plants treated with 1-Methyl tryptophan (1-MT), against Pseudomonas syringae pv. tomato DC3000 (Pst). Computational studies indicate that SlHBP2 is annotated as a SOUL heme-binding family protein. Remarkably, recombinant SlHBP2 demonstrated significant efficacy in inhibiting the growth of Pst within a concentration range of 3-25 µg/mL. Moreover, SlHBP2 exhibited potent antimicrobial effects against other microorganisms, including Xanthomonas vesicatoria (Xv), Clavibacter michiganensis subsp. michiganensis (Cmm), and Botrytis cinerea. To understand the mechanism of action employed by SlHBP2 against Pst, various techniques such as microscopy and fluorescence assays were employed. The results revealed that SlHBP2 disrupts the bacterial cell wall and causes leakage of intracellular contents. To summarize, the findings suggest that SlHBP2 has significant antimicrobial properties, making it a potential antimicrobial agent against a wide range of pathogens. Although further studies are warranted to explore the full potential of SlHBP2 and its suitability in various applications.

Insight into the antibacterial mechanism of Cu-enriched sol-gel coatings employing proteomics.

Advanced antibacterial biomaterials can help reduce the severe consequences of infections. Using copper compounds is an excellent option to achieve this goal; they offer a combination of regenerative and antimicrobial functions. In this study, new CuCl2-doped sol-gel coatings were developed and physicochemically characterised. Their osteogenic and inflammatory responses were tested in vitro using human osteoblasts and THP-1 macrophages. Their antibacterial effect was evaluated using Escherichia coli and Staphylococcus aureus. The Cu influence on the adsorption of human serum proteins was analysed employing proteomics. The materials released Cu2+ and were not cytotoxic. The osteoblasts in contact with these materials showed an increased ALP, BMP2 and OCN gene expression. THP-1 showed an increase in pro-inflammatory markers related to M1 polarization. Moreover, Cu-doped coatings displayed a potent antibacterial behaviour against E. coli and S. aureus. The copper ions affected the adsorption of proteins related to immunity, coagulation, angiogenesis, fibrinolysis, and osteogenesis. Interestingly, the coatings had increased affinity to proteins with antibacterial functions and proteins linked to the complement system activation that can lead to direct bacterial killing via large pore-forming complexes. These results contribute to our understanding of the antibacterial mechanisms of Cu-biomaterials and their interaction with biological systems.

Exploiting Tomato Genotypes to Understand Heat Stress Tolerance.

Increased temperatures caused by climate change constitute a significant threat to agriculture and food security. The selection of improved crop varieties with greater tolerance to heat stress is crucial for the future of agriculture. To overcome this challenge, four traditional tomato varieties from the Mediterranean basin and two commercial genotypes were selected to characterize their responses at high temperatures. The screening of phenotypes under heat shock conditions allowed to classify the tomato genotypes as: heat-sensitive: TH-30, ADX2; intermediate: ISR-10 and Ailsa Craig; heat-tolerant: MM and MO-10. These results reveal the intra-genetical variation of heat stress responses, which can be exploited as promising sources of tolerance to climate change conditions. Two different thermotolerance strategies were observed. The MO-10 plants tolerance was based on the control of the leaf cooling mechanism and the rapid RBOHB activation and ABA signaling pathways. The variety MM displayed a different strategy based on the activation of HSP70 and 90, as well as accumulation of phenolic compounds correlated with early induction of PAL expression. The importance of secondary metabolism in the recovery phase has been also revealed. Understanding the molecular events allowing plants to overcome heat stress constitutes a promising approach for selecting climate resilient tomato varieties.

Resistance Induction in Olive Tree (Olea europaea) Against Verticillium Wilt by Two Beneficial Microorganisms and a Copper Phosphite Fertilizer.

Enhancement of the natural defenses of a plant by beneficial microorganisms, i.e., endophytic bacteria and fungi or fertilizers such as copper phosphonates, could result in a potential alternative strategy against verticillium wilt of olive tree (Olea europaea). In this study, two beneficial microorganisms (the fungus Aureobasidium pullulans AP08 and the bacterium Bacillus amyloliquefaciens PAB-024) and a phosphonate salt copper phosphite (CuPh) were evaluated for their effectiveness as host resistance inducers against Verticillium dahliae in olive. To this end, 6-month-old healthy olive plants of the susceptible cultivar Picual were treated by foliar or root applications by spraying 15 ml per plant or by irrigation with 350 ml per plant of the dilutions of each product (CuPh: 3 or 10 ml l-1, respectively; PAB-024: 108 UFC ml-1; AP08: 106 UFC ml-1). Treatments were conducted weekly from 2 weeks before inoculation to 10 days after inoculation. A cornmeal-water-sand mixture (1:2:9; w:v:w) colonized by V. dahliae was used for plant inoculation. Additionally, treated and noninoculated, nontreated and inoculated, and nontreated and noninoculated plants were included for comparative purposes. Disease severity progress and shoot fresh weight were assessed. Parameters involved in plant resistance were monitored through determination and quantification of reactive oxygen species (ROS) response (H2O2), and evaluation of hormones was done by gene expression analysis. Aureobasidium pullulans and CuPh were the most effective in disease reduction in planta by foliar or root application, respectively. Plants treated with CuPh showed significantly higher shoot fresh weight compared to the other treatments. ROS was significantly enhanced in plants treated with B. amyloliquefaciens PAB-024 compared to the rest of treatments and control. With regard to the evaluation of hormones, high levels of salicylic acid were detected on leaves from all treatment combinations, but without significant enhancements compared to the nontreated control. Regarding the gene expression related to salicylic acid, only the WRKY5 gene has shown a strong enhancement in the treatment with B. amyloliquefaciens. On the other hand, a strong accumulation of jasmonic acid and jasmonic acid-isoleucine in plants treated with A. pullulans was observed in all the tissues analyzed and also in the roots of plants treated with B. amyloliquefaciens and CuPh.

Jasmonic acid pathway is required in the resistance induced by Acremonium sclerotigenum in tomato against Pseudomonas syringae.

The use of fungal endophytes is considered as a new tool to confer resistance in plants against stresses. However, the mechanisms involved in colonization as well as in the induction of resistance by the endophytes are usually unclear. In this work, we tested whether a fungal endophyte isolated from an ancestor of wheat could induce resistance in plants of a different class from the ones that were isolated from the beginning. Seeds of Solanum lycopersicum were inoculated with Acremonium sclerotigenum and after four weeks, seedlings were inoculated with the bacterium Pseudomonas syringae pv tomato. Plants inoculated with endophytes showed significantly lower symptoms of infection as well as lower levels of colony forming units compared with control plants. Moreover, the presence of the endophytes induced an enhancement of Jasmonic acid (JA) upon inoculation with P. syringae compared with endophyte free plants. To ascertain the implication of JA in the resistance induced by A. sclerotigenum, two mutants defective in JA were tested. Results showed that the endophyte is not able to induce resistance in the mutant spr2, which is truncated in the first step of JA biosynthesis. On the contrary, acx1 mutant plants, which are unable to synthesize JA from OPC8, show a phenotype similar to wild type plants. Moreover, experiments with GFP-tagged endophytes showed no differences in the colonization in both mutants. In conclusion, the jasmonic acid pathway is required for the resistance mediated by the endophyte A. sclerotigenum in tomato against the biotrophic bacterium P. syringae but is not necessary for the colonization.

Putrescine: A Key Metabolite Involved in Plant Development, Tolerance and Resistance Responses to Stress.

Putrescine (Put) is the starting point of the polyamines (PAs) pathway and the most common PA in higher plants. It is synthesized by two main pathways (from ornithine and arginine), but recently a third pathway from citrulline was reported in sesame plants. There is strong evidence that Put may play a crucial role not only in plant growth and development but also in the tolerance responses to the major stresses affecting crop production. The main strategies to investigate the involvement of PA in plant systems are based on the application of competitive inhibitors, exogenous PAs treatments, and the most efficient approaches based on mutant and transgenic plants. Thus, in this article, the recent advances in understanding the role of this metabolite in plant growth promotion and protection against abiotic and biotic stresses will be discussed to provide an overview for future research.

Putrescine biosynthetic pathways modulate root growth differently in tomato seedlings grown under different N sources.

The biosynthesis of putrescine is mainly driven by arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). Hence, in this study, we generated independent ADC and ODC transgenic silenced tomato lines (SilADC and SilODC, respectively) to test the effect of defective ADC and ODC gene expression on root development under nitrate (NN) or ammonium (NA) conditions. The results showed that SilODC seedlings displayed an increase in ADC expression that led to polyamine accumulation, suggesting a compensatory effect of ADC. However, this effect was not observed in SilADC seedlings. These pathways are involved in different growth processes. The SilADC seedlings showed an increase in fresh weight, shoot length, lateral root number and shoot:root ratio under the NN source and an enhancement in fresh weight, and shoot and root length under NA conditions. However, SilODC seedlings displayed greater weight and shoot length under the NN source, whereas a decrease in lateral root density was found under NA conditions. Moreover, two overexpressed ODC lines were generated to check the relevance of the compensatory effect of the ADC pathway when ODC was silenced. These overexpressed lines showed not only an enhancement of almost all the studied growth parameters under both N sources but also an amelioration of ammonium syndrome under NA conditions. Together, these results reflect the importance of both pathways in plant growth, particularly ODC silencing, which requires compensation by ADC induction.

The Botrytis cinerea Crh1 transglycosylase is a cytoplasmic effector triggering plant cell death and defense response.

Crh proteins catalyze crosslinking of chitin and glucan polymers in fungal cell walls. Here, we show that the BcCrh1 protein from the phytopathogenic fungus Botrytis cinerea acts as a cytoplasmic effector and elicitor of plant defense. BcCrh1 is localized in vacuoles and the endoplasmic reticulum during saprophytic growth. However, upon plant infection, the protein accumulates in infection cushions; it is then secreted to the apoplast and translocated into plant cells, where it induces cell death and defense responses. Two regions of 53 and 35 amino acids are sufficient for protein uptake and cell death induction, respectively. BcCrh1 mutant variants that are unable to dimerize lack transglycosylation activity, but are still able to induce plant cell death. Furthermore, Arabidopsis lines expressing the bccrh1 gene exhibit reduced sensitivity to B. cinerea, suggesting a potential use of the BcCrh1 protein in plant immunization against this necrotrophic pathogen.

1-Methyltryptophan Treatment Increases Defense-Related Proteins in the Apoplast of Tomato Plants.

The activation of induced resistance in plants may enhance the production of defensive proteins to avoid the invasion of pathogens. In this way, the composition of the apoplastic fluid could represent an important layer of defense that plants can modify to avoid the attack. In this study, we performed a proteomic study of the apoplastic fluid from plants treated with the resistance inducer 1-methyltryptophan (1-MT) as well as infected with Pseudomonas syringae pv. tomato (Pst). Our results showed that both the inoculation with Pst and the application of the inducer provoke changes in the proteomic composition in the apoplast enhancing the accumulation of proteins involved in plant defense. Finally, one of the identified proteins that are overaccumulated upon the treatment have been expressed in Escherichia coli and purified in order to test their antimicrobial effect. The result showed that the tested protein is able to reduce the growth of Pst in vitro. Taken together, in this work, we described the proteomic changes in the apoplast induced by the treatment and by the inoculation, as well as demonstrated that the proteins identified have a role in the plant protection.

Exogenous Carbon Compounds Modulate Tomato Root Development.

NO3- is not only a nutrient, but also a signaling compound that plays an important role in several plant processes, like root development. The present study aimed to investigate the effect of three different exogenous C compounds (sucrose, glucose, 2-oxoglutarate) added to NO3- nutrition on C/N, auxin and antioxidant metabolisms in 10-day-old tomato seedlings. Sucrose and glucose supplementation enhanced primary root (PR) length, lateral root number and root density, while 2-oxoglutarate negatively affected them. This phenomenon was accompanied by a slight increase in NRT2.1 and GS1 gene expression, together with an increase in LAX2 and LAX3 and a decrease in LAX4 in the roots growing under sucrose and glucose sources. The addition of 2-oxoglutarate enhanced the expression of NiR, GDH, PEPC1, LAX1, LAX3 and the antioxidant gene SOD Cl. Taken together, these findings contribute to a better understanding of how these C sources can modulate N uptake and C/N, auxin and antioxidant gene expression, which could be useful for improving nitrogen use efficiency.

The Apoplast: A Key Player in Plant Survival.

The apoplast comprises the intercellular space, the cell walls, and the xylem. Important functions for the plant, such as nutrient and water transport, cellulose synthesis, and the synthesis of molecules involved in plant defense against both biotic and abiotic stresses, take place in it. The most important molecules are ROS, antioxidants, proteins, and hormones. Even though only a small quantity of ROS is localized within the apoplast, apoplastic ROS have an important role in plant development and plant responses to various stress conditions. In the apoplast, like in the intracellular cell compartments, a specific set of antioxidants can be found that can detoxify the different types of ROS produced in it. These scavenging ROS components confer stress tolerance and avoid cellular damage. Moreover, the production and accumulation of proteins and peptides in the apoplast take place in response to various stresses. Hormones are also present in the apoplast where they perform important functions. In addition, the apoplast is also the space where microbe-associated molecular Patterns (MAMPs) are secreted by pathogens. In summary, the diversity of molecules found in the apoplast highlights its importance in the survival of plant cells.

Tomato root development and N assimilation depend on C and ABA content under different N sources.

Root plasticity is controlled by hormonal homeostasis and nutrient availability. In this work, we have determined the influence of different N regimens on growth parameters and on the expression of genes involved in auxin transport and N-assimilation in tomato seedlings. NH4+ nutrition led to an inhibitory effect on root fresh weight (FW), lateral root (LR) number and root density, while an increase in the primary root (PR) length was observed. The expression of N assimilation genes GS2 and ASN1, is affected by NH4+ nutrition. Moreover, in order to relieve the toxic effect of NH4+ on root development, glucose or 2-oxoglutarate was supplied as a C source during NH4+ treatment. The addition of 2-oxoglutarate improved root parameters compared to the NH4+ regimen. N-assimilation gene analysis showed that NH4+-fed tomato plants try to alleviate the toxic effect by concurrently upregulating ASN1 and anaplerotic PEPC2 expression, whereas when 2-oxoglutarate is supplied, ASN1 induction was not observed. The addition of both C skeletons induced the expression of the ROS-scavenging genes GSH and SOD. In addition, since ABA plays a role in root development, the ABA-synthesis-defective mutant flacca was studied under NO3- and NH4+ regimens. It displayed a decrease in LR number under NO3- conditions, whereas, the NH4+-fed seedlings showed a decrease solely in PR length that was reverted when ABA was exogenously supplied. Moreover, flacca seedlings displayed a reprogramming of the N/C assimilation genes. Altogether, these results reflect the importance of N and C sources and ABA homeostasis in root development of tomato seedlings.

Role of Jasmonic Acid Pathway in Tomato Plant-Pseudomonas syringae Interaction.

The jasmonic acid pathway has been considered as the backbone of the response against necrotrophic pathogens. However, a hemi-biotrophic pathogen, such as Pseudomonas syringae, has taken advantage of the crosstalk between the different plant hormones in order to manipulate the responses for its own interest. Despite that, the way in which Pseudomonas syringae releases coronatine to activate jasmonic acid-derived responses and block the activation of salicylic acid-mediated responses is widely known. However, the implication of the jasmonic intermediates in the plant-Pseudomonas interaction is not studied yet. In this work, we analyzed the response of both, plant and bacteria using SiOPR3 tomato plants. Interestingly, SiOPR3 plants are more resistant to infection with Pseudomonas. The gene expression of bacteria showed that, in SiOPR3 plants, the activation of pathogenicity is repressed in comparison to wild type plants, suggesting that the jasmonic acid pathway might play a role in the pathogenicity of the bacteria. Moreover, treatments with JA restore the susceptibility as well as activate the expression of bacterial pathogenicity genes. The observed results suggest that a complete jasmonic acid pathway is necessary for the susceptibility of tomato plants to Pseudomonas syringae.

Ammonium mediated changes in carbon and nitrogen metabolisms induce resistance against Pseudomonas syringae in tomato plants.

Predominant NH4+ nutrition causes an "ammonium syndrome" that induces metabolic changes and thereby provides resistance against Pseudomonas syringae infection through the activation of systemic acquired acclimation (SAA). Hence, to elucidate the mechanisms underlying NH4+-mediated SAA, the changes in nutrient balance and C and N skeletons were studied in NH4+-treated plants upon infection by P. syringae. A general decrease in cation and an increase in anion levels was observed in roots and leaves of NH4+-treated plants. Upon NH4+-based nutrition and infection, tomato leaves showed an accumulation of S, P, Zn, and of Mn. Mn accumulation might be required for ROS detoxification since it acts as a cofactor of superoxide dismutase (SOD). Primary metabolism was modified in both tissues of NH4+-fed plants to counteract NH4+ toxicity by decreasing TCA intermediates. A significant increase in Arg, Gln, Asn, Lys, Tyr, His and Leu was observed in leaves of NH4+-treated plants. The high level of the putrescine precursor Arg hints towards the importance of the Glu pathway as a key metabolic check-point in NH4+-treated and infected plants. Taken together, NH4+-fed plants displayed a high level of basal responses allowing them to activate SAA and to trigger defense responses against P. syringae through nutrient imbalances and changes in primary metabolism.

1-Methyltryptophan Modifies Apoplast Content in Tomato Plants Improving Resistance Against Pseudomonas syringae.

Plants can produce numerous natural products, many of which have been shown to confer protection against microbial attack. In this way, we identified 1-methyltryptophan (1-MT), a natural compound produced by tomato plants in response to Pseudomonas syringae attack, whose application by soil drench provided protection against this pathogen. In the present work, we have studied the mechanisms underlying this protection. The results demonstrated that 1-MT can be considered a new activator of plant defense responses that acts by inhibiting the stomatal opening produced by coronatine (COR) and could thereby, prevent bacteria entering the mesophyll. Besides, 1-MT acts by blocking the jasmonic acid (JA) pathway that, could avoid manipulation of the salicylic acid (SA) pathway by the bacterium, and thus hinder its growth. Although the concentration of 1-MT reached in the plant did not show antimicrobial effects, we cannot rule out a role for 1-MT acting alone because it affects the expression of the fliC gene that is involved in synthesis of the flagellum. These changes would result in reduced bacterium motility and, therefore, infective capacity. The results highlight the effect of a tryptophan derivative on induced resistance in plants.

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.

An untargeted global metabolomic analysis reveals the biochemical changes underlying basal resistance and priming in Solanum lycopersicum, and identifies 1-methyltryptophan as a metabolite involved in plant responses to Botrytis cinerea and Pseudomonas syringae.

In this study, we have used untargeted global metabolomic analysis to determine and compare the chemical nature of the metabolites altered during the infection of tomato plants (cv. Ailsa Craig) with Botrytis cinerea (Bot) or Pseudomonas syringae pv. tomato DC3000 (Pst), pathogens that have different invasion mechanisms and lifestyles. We also obtained the metabolome of tomato plants primed using the natural resistance inducer hexanoic acid and then infected with these pathogens. By contrasting the metabolomic profiles of infected, primed, and primed + infected plants, we determined not only the processes or components related directly to plant defense responses, but also inferred the metabolic mechanisms by which pathogen resistance is primed. The data show that basal resistance and hexanoic acid-induced resistance to Bot and Pst are associated with a marked metabolic reprogramming. This includes significant changes in amino acids, sugars and free fatty acids, and in primary and secondary metabolism. Comparison of the metabolic profiles of the infections indicated clear differences, reflecting the fact that the plant's chemical responses are highly adapted to specific attackers. The data also indicate involvement of signaling molecules, including pipecolic and azelaic acids, in response to Pst and, interestingly, to Bot. The compound 1-methyltryptophan was shown to be associated with the tomato-Pst and tomato-Bot interactions as well as with hexanoic acid-induced resistance. Root application of this Trp-derived metabolite also demonstrated its ability to protect tomato plants against both pathogens.

Silencing of OPR3 in tomato reveals the role of OPDA in callose deposition during the activation of defense responses against Botrytis cinerea.

Cis-(+)-12-oxo-phytodienoic acid (OPDA) is likely to play signaling roles in plant defense that do not depend on its further conversion to the phytohormone jasmonic acid. To elucidate the role of OPDA in Solanum lycopersicum (tomato) plant defense, we have silenced the 12-oxophytodienoate reductase 3 (OPR3) gene. Two independent transgenic tomato lines (SiOPR3-1 and SiOPR3-2) showed significantly reduced OPR3 expression upon infection with the necrotrophic pathogen Botrytis cinerea. Moreover, SiOPR3 plants are more susceptible to this pathogen, and this susceptibility is accompanied by a significant decrease in OPDA levels and by the production of JA-Ile being almost abolished. OPR3 silencing also leads to a major reduction in the expression of other genes of the jasmonic acid (JA) synthesis and signaling pathways after infection. These results confirm that in tomato plants, as in Arabidopsis, OPR3 determines OPDA availability for JA biosynthesis. In addition, we show that an intact JA biosynthetic pathway is required for proper callose deposition, as its pathogen-induced accumulation is reduced in SiOPR3 plants. Interestingly, OPDA, but not JA, treatment restored basal resistance to B. cinerea and induced callose deposition in SiOPR3-1 and SiOPR3-2 transgenic plants. These results provide clear evidence that OPDA by itself plays a major role in the basal defense of tomato plants against this necrotrophic pathogen.

Resistance 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.

Hexanoic acid is a resistance inducer that protects tomato plants against Pseudomonas syringae by priming the jasmonic acid and salicylic acid pathways.

Hexanoic acid-induced resistance (Hx-IR) is effective against several pathogens in tomato plants. Our study of the mechanisms implicated in Hx-IR against Pseudomonas syringae pv. tomato DC3000 suggests that hexanoic acid (Hx) treatment counteracts the negative effect of coronatine (COR) and jasmonyl-isoleucine (JA-Ile) on the salicylic acid (SA) pathway. In Hx-treated plants, an increase in the expression of jasmonic acid carboxyl methyltransferase (JMT) and the SA marker genes PR1 and PR5 indicates a boost in this signalling pathway at the expense of a decrease in JA-Ile. Moreover, Hx treatment potentiates 12-oxo-phytodienoic acid accumulation, which suggests that this molecule might play a role per se in Hx-IR. These results support a positive relationship between the SA and JA pathways in Hx-primed plants. Furthermore, one of the mechanisms of virulence mediated by COR is stomatal re-opening on infection with P. syringae. In this work, we observed that Hx seems to inhibit stomatal opening in planta in the presence of COR, which suggests that, on infection in tomato, this treatment suppresses effector action to prevent bacterial entry into the mesophyll.