The structural basis for activation of plant immunity by bacterial effector protein AvrPto

Pathogenic microbes use effectors to enhance susceptibility in host plants. However, plants have evolved a sophisticated immune system to detect these effectors using cognate disease resistance proteins, a recognition that is highly specific, often elicits rapid and localized cell death, known as a hypersensitive response, and thus potentially limits pathogen growth. Despite numerous genetic and biochemical studies on the interactions between pathogen effector proteins and plant resistance proteins, the structural bases for such interactions remain elusive. The direct interaction between the tomato protein kinase Pto and the Pseudomonas syringae effector protein AvrPto is known to trigger disease resistance and programmed cell death through the nucleotide-binding site/leucine-rich repeat (NBS-LRR) class of disease resistance protein Prf. Here we present the crystal structure of an AvrPto-Pto complex. Contrary to the widely held hypothesis that AvrPto activates Pto kinase activity, our structural and biochemical analyses demonstrated that AvrPto is an inhibitor of Pto kinase in vitro. The AvrPto-Pto interaction is mediated by the phosphorylation-stabilized P+1 loop and a second loop in Pto, both of which negatively regulate the Prf-mediated defences in the absence of AvrPto in tomato plants. Together, our results show that AvrPto derepresses host defences by interacting with the two defence-inhibition loops of Pto.

Tomato MAPKs LeMPK1, LeMPK2, and LeMPK3 function in the systemin-mediated defense response against herbivorous insects

Systemin is a wound-signaling peptide that mediates defenses of tomato plants against herbivorous insects. Perception of systemin by the membrane-bound receptor SR160 results in activation of MAPKs, synthesis of jasmonic acid (JA), and expression of defense genes. To test the function of MAPKs in the response to systemin, we used virus-induced gene silencing (VIGS) in plants that overexpress the systemin precursor prosystemin (35S::prosys plants). These transgenic plants accumulate high levels of defense proteins and exhibit increased resistance to herbivorous insects. Cosilencing of the MAPKs MPK1 and MPK2 reduced MPK1/2 kinase activity, JA biosynthesis, and expression of JA-dependent defense genes. Application of methyl-JA restored the full defense response. These data show that MPK1 and MPK2 are essential components of the systemin signaling pathway and most likely function upstream of JA biosynthesis. MPK1 and MPK2 are 95% identical at the amino acid level. Specific VIGS of only MPK1 or MPK2 resulted in the same reduction of defense gene expression as cosilencing of MPK1 and MPK2, indicating that gene dosage effects may be important for MPK signaling. In addition, VIGS of the closely related MPK3 also reduced systemin-induced defense responses. The function of MPK1/2 and orthologs in pathogen-induced defenses is well established. Here we show that cosilencing of MPK1 and MPK2 compromised prosystemin-mediated resistance to Manduca sexta (Lepidoptera) herbivory, demonstrating that MPK1 and MPK2 are also required for successful defenses against herbivorous insects.

Expression of a truncated ripening inhibitor (RIN) protein from tomato and production of an anti-RIN antibody

The tomato ripening mutant, ripening inhibitor (rin), whose fruits fails to ripen, has been identified and widely studied. The RIN gene has been cloned. Here we present the expression of a truncated form of the RIN protein from tomato and the preparation of a polyclonal antibody against it. The resulting antibody recognized the RIN of crude protein extracts from different tomato tissues. The protein level of RIN in tomato was detected with this antibody by western blot, which suggested the accumulation of RIN protein increased gradually during tomato fruit ripening.

Fruit-specific expression of the human immunodeficiency virus type 1 tat gene in tomato plants and its immunogenic potential in mice

The human immunodeficiency virus type 1 (HIV-1) Tat protein is considered a potential candidate vaccine antigen. In an effort to design a strategy for noninvasive vaccination against HIV-1, we developed transgenic tomatoes expressing the Tat protein. Two independent plants testing positive in transgene detection analysis were selected and grown to maturity. Monoclonal antibodies against Tat recognized a protein of the expected size. Interestingly, expression of Tat seemed to be toxic to the plant, as in all cases the fruit exhibited underdeveloped reproductive structures and no seeds. Nine groups of 10 pathogen-free BALB/c male mice were primed either orally, intraperitoneally, or intramuscularly with 10 mg of tomato fruit extract derived from transgenic or wild-type plants and with 10 microg of Tat86 recombinant protein. Mice were immunized at days 0, 14, and 28, and given boosters after 15 weeks; sera were drawn 7 days after each booster, and the antibody titer was determined by enzyme-linked immunosorbent assay. All three immunization approaches induced the development of a strong anti-Tat immunological response, which increased over time. Isotype subclass determination showed the presence of mucosal (immunoglobulin A) immunity soon after the beginning of the oral immunization protocol, and the data were confirmed by the presence of anti-Tat antibodies in fecal pellets and in vaginal washes. We also demonstrated that sera from immunized mice inhibited with high efficiency recombinant Tat-dependent transactivation of the HIV-1 long terminal repeat promoter. This neutralization activity might be relevant for the suppression of extracellular Tat activities, which play an important role in HIV disease development.

Expression of the human hepatitis B virus large surface antigen gene in transgenic tomato plants

The original hepatitis B virus (HBV) large surface antigen gene was synthesized. In order to optimize the expression of this gene in tomato plants, the tobacco pathogenesis-related protein S signal peptide was fused to the 5' end of the modified gene and the sequence encoding amino acids S, E, K, D, E, and L was placed at the 3' end. The gene encoding the modified HBV large surface antigen under the control of a fruit-specific promoter was constructed and expressed in transgenic tomato plants. The expression of the antigen from transgenic plants was confirmed by PCR and reverse transcriptase PCR. Enzyme-linked immunoassays using a monoclonal antibody directed against human serum-derived HBsAg revealed that the maximal level of HBsAg was about 0.02% of the soluble protein in transgenic tomato fruit. The amount of HBsAg in mature fruits was found to be 65- to 171-fold larger than in small or medium fruits and leaf tissues. Examination of transgenic plant samples by transmission electron microscopy proved that HBsAg had been expressed and had accumulated. The HBsAg protein was capable of assembling into capsomers and virus-like particles. To our knowledge, this is the first time the HBV large surface antigen has been expressed in plants. This work suggests the possibility of producing a new alternative vaccine for human HBV.

The double-resistance-breaking Tomato mosaic virus strain ToMV1-2 contains two independent single resistance-breaking domains

Tomato mosaic virus (ToMV) causes a serious loss of yield and fruit quality in tomato crops. To control ToMV, three resistance genes, Tm-1, Tm-2, and Tm-2(2) from wild tomato species were introduced into commercial tomato cultivars. Soon after, however, single and, rarely, double-resistance-breaking virus strains for Tm-1 and Tm-2 emerged. Sequence analysis of a Tm-1/Tm-2 double-resistance-breaking virus, designated ToMV1-2, revealed 30 nucleotide substitutions compared with wild-type ToMV. Of these, six substitutions result in amino acid exchanges. Two exchanges are in the methyl transferase/helicase domain of the ToMV1-2 130/180-kDa proteins (D-1097 to V, R-1100 to Q), two exchanges are found in the 30-kDa movement protein (MP; E-52 to K, E-133 to K), and two exchanges are in the coat protein (I-22 to V, A-87 to S). Construction of chimeric full-length viral cDNA clones containing the base substitutions resulting in altered amino acids, either in the 130/180 kDa proteins or the MP, revealed that the amino acid exchanges in the 130/180-kDa proteins enable ToMV1-2 to break the Tm-1 resistance, while those in the MP enable ToMV1-2 to overcome the Tm-2 resistance. Furthermore, a novel Tm-1/Tm-2 double-resistance-breaking virus was generated by combining the Tm-1-breaking domain of ToMV1-2 and the MP of a new virus, ToMV2, containing the amino acid exchanges E-133 to K and N-135 to S. Together, the data suggest that double-resistance-breaking ToMV1-2 may have resulted from recombination between Tm-1 and Tm-2 single resistance-breaking virus strains.

Combinatorially selected defense peptides protect plant roots from pathogen infection

Agricultural productivity and sustainability are continually challenged by emerging and indigenous pathogens. Currently, many pathogens can be combatted only with biocides or environmentally dangerous fumigants. Here, we report a rapid and pathogen-specific strategy to reduce infection by organisms that target plant roots. Combinatorially selected defense peptides, previously shown to effect premature encystment of Phytophthora capsici zoospores, were fused to maize cytokinin oxidase/dehydrogenase as a display scaffold. When expressed in tomato roots, the peptide-scaffold constructs were secreted and accumulated to sufficient concentrations in the rhizosphere to induce zoospore encystment and thereby deter taxis to the root surface. Pathogen infection was significantly inhibited in roots expressing bioactive peptides fused to the maize cytokinin oxidase/dehydrogenase scaffold. This peptide-delivery technology is broadly applicable for rapid development of plant defense attributes against plant pathogens.

Reduced allergenicity of tomato fruits harvested from Lyc e 1–silenced transgenic tomato plants

BACKGROUND

Profilin is a small actin-binding protein that contributes to the allergenic potency of many fruits and vegetables, including tomato. Two highly similar genes encoding tomato profilin have been isolated and designated as allergen Lyc e 1.01 and Lyc e 1.02.

OBJECTIVE

The aim of the study was to generate profilin-reduced hypoallergenic tomato fruits by silencing of both genes in transgenic tomato plants by means of RNA interference (RNAi).

METHODS

The efficiency of gene silencing was documented by means of Northern blotting, immunoblotting, and skin prick testing.

RESULTS

Quantification of the remaining protein revealed that profilin accumulation in transgenic fruits was decreased 10-fold compared with that seen in untransformed controls. This decrease was sufficient to cause a reduced allergenic reactivity in patients with tomato allergy, as determined with skin prick tests. Because most patients with tomato allergy are not monosensitized to profilin, the IgE reactivity to the profilin-silenced tomato fruits in vivo varied widely between individuals tested.

CONCLUSION

We could demonstrate the efficient silencing of both profilin genes in transgenic tomato plants using RNAi. This resulted in Lyc e 1-diminished tomato fruits, providing proof of concept and demonstrating that RNAi can be used to design allergen-reduced food. However, simultaneous silencing of multiple allergens will be required to design hypoallergenic tomatoes.

CLINICAL IMPLICATIONS

Our findings demonstrate the feasibility of creating low-allergenic food by using RNAi. This concept constitutes a novel approach to allergen avoidance.

The tomato NBARC-LRR protein Prf interacts with Pto kinase in vivo to regulate specific plant immunity

Immunity in tomato (Solanum lycopersicum) to Pseudomonas syringae bacteria expressing the effector proteins AvrPto and AvrPtoB requires both Pto kinase and the NBARC-LRR (for nucleotide binding domain shared by Apaf-1, certain R gene products, and CED-4 fused to C-terminal leucine-rich repeats) protein Prf. Pto plays a direct role in effector recognition within the host cytoplasm, but the role of Prf is unknown. We show that Pto and Prf are coincident in the signal transduction pathway that controls ligand-independent signaling. Pto and Prf associate in a coregulatory interaction that requires Pto kinase activity and N-myristoylation for signaling. Pto interacts with a unique Prf N-terminal domain outside of the NBARC-LRR domain and resides in a high molecular weight recognition complex dependent on the presence of Prf. In this complex, both Pto and Prf contribute to specific recognition of AvrPtoB. The data suggest that the role of Pto is confined to the regulation of Prf and that the bacterial effectors have evolved to target this coregulatory molecular switch.

Reduction of allergenic proteins by the effect of the ripening inhibitor (rin) mutant gene in an F1 hybrid of the rin mutant tomato

The ripening inhibitor (rin) mutant tomato yields non-ripening fruit, and the rin hybrid fruit (RIN/rin) shows an intermediate phenotype between the wild and mutant fruit, that is, red-ripe and extended shelf life. We found by a microarray analysis that the genes encoding possible allergenic proteins were expressed at a significantly lower level in the rin hybrid fruit than in the wild-type fruit. These allergenic proteins, which were beta-fructofuranosidase and polygalacturonase 2A (PG-2A), were confirmed to accumulate at a lower level in the rin hybrid fruit than in the wild-type fruit. The immunoglobulin E (IgE) in serum from a tomato-allergic patient showed lower reactivity to the extract of the rin hybrid fruit than to that of the wild fruit. These results suggest that the rin gene has the potential to regulate allergen accumulation in tomato fruit.

Skin prick tests reveal stable and heritable reduction of allergenic potency of gene-silenced tomato fruits

BACKGROUND

Today, for patients with food allergy, the only possibility to prevent allergic reactions is avoidance of the allergenic food. Genetic engineering of hypoallergenic plants by means of RNA interference (RNAi) could be an approach to improve the quality of life of subjects with food allergy.

OBJECTIVES

We sought to achieve stable inhibition of expression of the allergenic nonspecific lipid transfer protein Lyc e 3 in tomato and to analyze the reduction of allergenicity in vitro by using histamine release assays and in vivo by using skin prick tests with transgenic tomato fruits.

METHODS

Gene silencing was performed by means of RNAi and monitored by using Western blotting with nonspecific lipid transfer protein-specific antibodies and sera from patients with tomato allergy. Dose-dependent basophil histamine release assays, prick-to-prick skin testing, and determination of endogenous histamine content were performed with fruits harvested from plants of the first and second generation to assess the allergenic potency compared with that of wild-type fruits.

RESULTS

We demonstrated that silencing of Lyc e 3 by means of RNAi contributes to reduced skin reactivity and is passed on to the next generation of fruits. A significant reduction of allergenic potency was determined in vitro and confirmed by using skin prick tests.

CONCLUSION

Taken together, these results indicate that RNAi technology is an effective tool to generate foods with reduced allergenicity.

CLINICAL IMPLICATIONS

Allergen-reduced plant foods might allow reduction of dietary restrictions for patients allergic to panallergen families.

Production of rotavirus-like particles in tomato (Lycopersicon esculentum L.) fruit by expression of capsid proteins VP2 and VP6 and immunological studies

A number of different antigens have been successfully expressed in transgenic plants, and some are currently being evaluated as orally delivered vaccines. Here we report the successful expression of rotavirus capsid proteins VP2 and VP6 in fruits of transgenic tomato plants. By western blot analysis, using specific antibodies, we determined that the VP2 and VP6 produced in plants have molecular weights similar to those found in native rotavirus. The plant-synthesized VP6 protein retained the capacity to form trimers. We were able to recover rotavirus virus-like particles from tomato fruit (i.e., tomatoes) by centrifugation on a sucrose cushion and to visualize them by electron microscopy. This result indicated that VP2/VP6 can self-assemble into virus-like particles (VLPs) in plant cells, even though only a small proportion of VP2/VP6 assembled into VLPs. To investigate immunogenicity, adult mice were immunized intraperitoneally (i.p.) three times with a protein extract from a transgenic tomatoes in adjuvant. We found that the transgenic tomato extract induced detectable levels of anti-rotavirus antibodies in serum; however, we did not determine the contribution of either the free rotavirus proteins or the VLPs to the induction of the antibody response. These results suggest the potential of plant-based rotavirus VLPs for the development of a vaccine against rotavirus infection.

Design of tomato fruits with reduced allergenicity by dsRNAi-mediated inhibition of ns-LTP (Lyc e 3) expression

Plant genetic engineering has the potential to introduce new allergenic proteins into foods but, at the same time, it can be used to remove established allergens. Here, we report the molecular characterization of Lyc e 3, a new tomato (Lycopersicon esculentum) allergen, and the efficient down-regulation of its expression in transgenic tomato plants. Following the identification of an immunoglobulin E (IgE)-binding 9-kDa polypeptide in tomato peel, designated Lyc e 3, its partial amino acid sequence was determined by N-terminal protein sequencing. Sequence comparison revealed that Lyc e 3 encodes a nonspecific lipid transfer protein (ns-LTP). In plants, ns-LTPs are encoded by large gene families which differ in primary amino acid sequence, expression and proposed cellular function. To identify Lyc e 3 encoding complementary DNAs (cDNAs), public tomato expressed sequence tag (EST) databases were screened for ns-LTP sequences. Following this strategy, two cDNAs, LTPG1 and LTPG2, with high homology to the N-terminal sequence of Lyc e 3, were identified. Ectopic expression of LTPG1 and LTPG2 in Escherichia coli, followed by immunoblotting, verified their IgE reactivity. Subsequently, transgenic tomato plants constitutively expressing LTPG1- or LTPG2-specific double-stranded RNA interference (dsRNAi) constructs were created and tested for the suppression of Lyc e 3 accumulation. Efficient silencing of Lyc e 3 was documented by Northern and Western blotting. In both cases, Lyc e 3 accumulation was decreased to levels below the detection limit (less than 0.5% of the wild-type protein). The allergenic potential of Lyc e 3-deficient tomato fruits was tested by measuring histamine release from sensitized human basophils stimulated with transgenic and parental lines. These assays revealed a strong (10- to 100-fold) decrease in histamine release of human basophils challenged with transgenic fruit extracts when compared with control extracts. These results demonstrate the feasibility of creating low allergenic tomato fruits by means of dsRNAi inhibition.

Type III effector AvrPtoB requires intrinsic E3 ubiquitin ligase activity to suppress plant cell death and immunity

Microbial pathogens of both plants and animals employ virulence factors that suppress the host immune response. The tomato pathogen Pseudomonas syringae injects the AvrPtoB type III effector protein into the plant cell to suppress programmed cell death (PCD) associated with plant immunity. AvrPtoB also inhibits PCD in yeast, indicating that AvrPtoB manipulates a conserved component of eukaryotic PCD. To identify host targets of AvrPtoB, we performed a yeast two-hybrid screen and identified tomato ubiquitin (Ub) as a strong AvrPtoB interactor. AvrPtoB is ubiquitinated in vitro and exhibits E3 Ub ligase activity in the presence of recombinant E1 activating enzyme and specific E2 Ub-conjugating enzymes. The C terminus of AvrPtoB is sufficient for both anti-PCD and E3 Ub ligase activities, suggesting the two functions are associated. Indeed, mutation of AvrPtoB lysine residues in the C terminus, between K512 and K529, disrupts AvrPtoB-Ub interactions, decreases AvrPtoB-mediated anti-PCD activity, and abrogates P. syringae pathogenesis of susceptible tomato plants. Remarkably, quantitative decreases in AvrPtoB anti-PCD activity are correlated with decreases in AvrPtoB ubiquitination and E3 Ub ligase activity. Overall, these data reveal a unique bacterial pathogenesis strategy, where AvrPtoB manipulates the host Ub system and requires intrinsic E3 Ub ligase activity to suppress plant immunity.

The Arabidopsis receptor kinase FLS2 binds flg22 and determines the specificity of flagellin perception

Flagellin, the main building block of the bacterial flagellum, acts as a pathogen-associated molecular pattern triggering the innate immune response in animals and plants. In Arabidopsis thaliana, the Leu-rich repeat transmembrane receptor kinase FLAGELLIN SENSITIVE2 (FLS2) is essential for flagellin perception. Here, we demonstrate the specific interaction of the elicitor-active epitope flg22 with the FLS2 protein by chemical cross-linking and immunoprecipitation. The functionality of this receptor was further tested by heterologous expression of the Arabidopsis FLS2 gene in tomato (Lycopersicon esculentum) cells. The perception of flg22 in tomato differs characteristically from that in Arabidopsis. Expression of Arabidopsis FLS2 conferred an additional flg22-perception system on the cells of tomato, which showed all of the properties characteristic of the perception of this elicitor in Arabidopsis. In summary, these results show that FLS2 constitutes the pattern-recognition receptor that determines the specificity of flagellin perception.

Oral rush desensitization with tomato: a case report

Adverse food reaction in which no immunological mechanism is demonstrated should be termed nonallergic food hypersensitivity or food intolerance. We present the case of a 12-year-old girl with a clinical history of abdominal pain, nausea, and general malaise after tomato intake which completely remitted with antihistamines. The patient underwent a complete allergy evaluation: skin prick tests, serum specific IgE and IgG4 tests to tomato, and double-blind placebo-controlled food challenge. Skin prick tests and specific IgE to tomato were negative while the food challenge was positive. At the end of the workup, the patient underwent an oral rush desensitizing treatment. At the end of the treatment the patient could eat a maintenance dose of 100 g of tomato daily with no side effects at all. This successful result suggests that the oral desensitizing treatment can be used in patients with nonallergic food hypersensitivity.

A bacterial inhibitor of host programmed cell death defenses is an E3 ubiquitin ligase

The Pseudomonas syringae protein AvrPtoB is translocated into plant cells, where it inhibits immunity-associated programmed cell death (PCD). The structure of a C-terminal domain of AvrPtoB that is essential for anti-PCD activity reveals an unexpected homology to the U-box and RING-finger components of eukaryotic E3 ubiquitin ligases, and we show that AvrPtoB has ubiquitin ligase activity. Mutation of conserved residues involved in the binding of E2 ubiquitin-conjugating enzymes abolishes this activity in vitro, as well as anti-PCD activity in tomato leaves, which dramatically decreases virulence. These results show that Pseudomonas syringae uses a mimic of host E3 ubiquitin ligases to inactivate plant defenses.

Biophoton distress flares signal the onset of the hypersensitive reaction

Detection of biophoton emission, a natural bioluminescence, has emerged as a non-destructive method to mark the onset of the hypersensitive resistance reaction in Arabidopsis, bean and tomato. Rapid biophoton emission in Arabidopsis requires an intact R-gene signalling network and increased levels of cytosolic calcium and nitric oxide. The burst of biophotons precedes macroscopic symptoms by several hours and its timing is characteristic for specific gene-for-gene interactions. The ability to monitor biophoton emission from whole plants in real time should allow detailed dissection of plant defence responses.

Virus-like particle expression and assembly in plants: hepatitis B and Norwalk viruses

Expression of vaccine antigens in plants and delivery via ingestion of transgenic plant material has shown promise in numerous pre-clinical animal studies and in a few clinical trials. A number of different viral antigens have been tested, and among the most promising are those that can assemble virus-like particles (VLP), which mimic the form of authentic virions and display neutralizing antibody epitopes. We have extensively studied plant expression, VLP assembly, and immunogenicity of hepatitis B surface antigen (HBsAg) and Norwalk virus capsid protein (NVCP). The HBsAg small protein (S protein) was found by TEM to assemble tubular membrane complexes derived from endoplasmic reticulum in suspension cultured cells of tobacco and soybean, and in potato leaf and tuber tissues. The potato material was immunogenic in mice upon delivery by ingestion. Here we describe the plant expression and immunogenicity of HBsAg middle protein (M protein or pre-S2 + S) which contains additional 55 amino acid pre-S2 region at N-terminus of the S protein. Plant-derived recombinant M protein provoked stronger serum antibody responses against HBsAg than did S protein when injected systemically in mice. We discuss implications for use of fusion proteins for enhanced immunogenicity and mucosal targeting of HBsAg, as well as delivery of heterologous fused antigens. NVCP expressed in plants assembled 38 nm virion-size icosahedral (T = 3) VLP, similar to those produced in insect cells. The VLP stimulated serum IgG and IgA responses in mice and humans when they were delivered by ingestion of fresh potato tuber. Here we show that freeze-drying of transgenic NVCP tomato fruit yielded stable preparations that stimulated excellent IgG and IgA responses against NVCP when fed to mice. However, the predominant VLP form in tomato fruit was the small 23 nm particle also observed in insect cell-derived NVCP.

Susceptibility of some Lycopersicon species and varieties to cucumber mosaic virus (CMV) and tobacco mosaic virus (TMV)

Susceptibility of 33 Lycopersicon species and varieties to Tobacco mosaic virus (TMV) and Cucumber mosaic virus (CMV) were studied. Plants were mechanically inoculated with the C/U1 strain of TMV and U/246 strain of CMV. Virus infection was checked by symptomatology, DAS ELISA and back inoculation (biotest). All the studied Lycopersicon species and varieties were susceptible to TMV-C/U1. L. esculentum Mill. convar. infiniens Lehm. var. flammatum Lehm., L. esculentum Mill. convar. fruticosum Lehm. var. speciosum Lehm. and L. esculentum Mill. convar. infiniens Lehm. var. validum Bail. showed extreme resistance to CMV-U/246. The other 30 species and varieties were susceptible to CMV-U/246. New compatible and incompatible host-virus relations have been reported. The extreme resistant Lycopersicon varieties could be used as resistance sources in tomato breeding.

A patch of surface-exposed residues mediates negative regulation of immune signaling by tomato Pto kinase

Tomato (Lycopersicon esculentum) Pto kinase specifically recognizes the Pseudomonas effector proteins AvrPto and AvrPtoB, leading to induction of defense responses and hypersensitive cell death. Structural modeling of Pto combined with site-directed mutagenesis identified a patch of surface-exposed residues required for native regulation of signaling. Mutations in this area resulted in constitutive gain-of-function (CGF) forms of Pto that activated AvrPto-independent cell death via the cognate signaling pathway. The patch overlaps the peptide binding region of the kinase catalytic cleft and is part of a broader region required for interaction with bacterial effectors. We propose that the negative regulatory patch is normally occupied by a peptide that represses Pto signaling. Furthermore, we found that Pto kinase activity was required for Avr-dependent activation but dispensable for signaling by CGF forms of Pto. This suggests that Pto signals by a conformational change rather than phosphorylation of downstream substrates in the defense signaling pathway.

Tomato profilin Lyc e 1: IgE cross-reactivity and allergenic potency

BACKGROUND

To date, very little data are available about the nature of tomato allergens. Immunoglobulin E (IgE) cross-reactive profilins have been suggested to account for allergic symptoms in patients suffering from tomato allergy.

METHODS

The cDNA of tomato profilin was amplified by reversely transcribed polymerase chain reaction (RT-PCR) from total RNA extracted from ripe tomato fruit. The gene was cloned into the pET101D expression plasmid and the protein was produced in Escherichia coli BL21. Purification was performed via poly-l-proline (PLP) affinity chromatography. IgE reactivity of recombinant tomato profilin was investigated by immunoblot and enzyme-linked immunosorbent assay. IgE-inhibition studies were performed to analyse cross-reactivity with other profilins. To determine the allergenic activity of the recombinant protein, basophil histamine release assays using sera of patients with adverse reactions to tomato were performed.

RESULTS

Profilin was identified as a new minor allergen in tomato fruits. The recombinant tomato profilin comprises 131 amino acids and high sequence identity to other allergenic food and pollen profilins. It was shown to be IgE-reactive with a prevalence of 22% (11/50) in tomato-allergic patients. In patients with tomato allergy and multiple sensitization to other foods and birch pollen, IgE directed against tomato profilin showed a strong cross-reactivity with profilins from plant food sources and birch pollen. The tomato profilin was able to induce mediator release from human basophils.

CONCLUSION

The tomato profilin is a minor allergen in tomato fruit. Thus, it shows biological activity, as confirmed by in vitro histamine release assays with human basophils and thereby has the potential to account for clinical symptoms in tomato-allergic patients.

[Designing of a candidate edible vaccine against hepatitis B and HIV on the basis of a transgenic tomato]

The synthetic chimeric gene TBI-HBS encoding the synthesis of immunogenic ENV and GAC epitopes of HIV-1 (immunogenes of T- and B-lymphocytes) and of the surface protein (HBsAg) of the hepatitis B virus was introduced into tomato plants var. Ventura by agrobacterial vector pBIN35TBI-HBS; transgenic tomato plants with the integrated gene TBI-HBS were generated. The integration of the TBI-HBS target gene was confirmed by PCR. The synthesis of antigenic proteins of TBI and HBsAg in fruits of transgenic tomato plants was displayed by immunoassay. The fruits of transgenic tomato plants were fed to experimental mice with a 1-week interval. On days 14 and 28, there was discovered a sufficiently high content of antibodies to the antigenic proteins of HBV and HIV-1 in serum of experimental animals. Antibodies were found in feces of experimental mice; no antibodies were found in the control group of mice. Hence, it was established that the TBI (HIV-1) and HBsAg (HBV) antigens were synthesized in transgenic tomato fruits due to the integrated construction of pBINNp35TBI-HBS in an amount that was enough to induce the immunogenic response in mice to the oral delivery of edible vaccine.