Expression Of Pathogenesis-related Genes Research Articles

Overexpressing sweetpotato peroxidase gene swpa4 affects nitric oxide production by activating the expression of reactive oxygen species- and nitric oxide-related genes in tobacco

Reactive oxygen species (ROS) and nitric oxide (NO) are key signaling molecules involved in various developmental and stress responses in plants. NO and ROS production, which is triggered by various stimuli, activates downstream signaling pathways to help plants cope with abiotic and biotic stresses. Recent evidence suggests that the interplay between NO and ROS signaling plays a critical role in regulating stress responses. However, the underlying molecular mechanism remains poorly understood. We previously reported that transgenic tobacco overexpressing the swpa4 peroxidase (POD) gene from sweetpotato exhibits increased tolerance to stress. Overexpression of swpa4 also induces the generation of H2O2 and activates the expression of various extracellular acidic pathogenesis-related (PR) genes. Here, we show that swpa4 positively regulates the expression of ROS- and NO-related genes in transgenic tobacco plants. Plants expressing swpa4 exhibited increased expression of ROS-related genes and increased ROS-related enzyme activity under normal conditions and H2O2 treatment, whereas the expression of NO associated 1 (NOA1) only increased under normal conditions. Moreover, plants overexpressing swpa4 showed increased NO levels under normal conditions and after treatment with the NO donor sodium nitroprusside (SNP). Interestingly, treatment with a POD inhibitor dramatically reduced NO levels in swpa4 transgenic plants. These findings suggest that swpa4 regulates H2O2 and NO homeostasis in plants under stress conditions, thereby establishing a possible molecular link between the NO and ROS signaling pathways.

Involvement of Arabidopsis thaliana endoplasmic reticulum KDEL-tailed cysteine endopeptidase 1 (AtCEP1) in powdery mildew-induced and AtCPR5-controlled cell death.

Programmed cell death (PCD) is a prerequisite for successful development and it limits the spread of biotrophic pathogens in a rapid hypersensitive response at the site of infection. KDEL-tailed cysteine endopeptidases (KDEL CysEP) are a subgroup of papain-type cysteine endopeptidases expressed in tissues undergoing PCD. In Arabidopsis, three KDEL CysEPs (AtCEP1, AtCEP2, and AtCEP3) are expressed. We have previously shown that AtCEP1 is a factor of basal resistance to powdery mildew caused by the biotrophic ascomycete Erysiphe cruciferarum, and is expressed in spatiotemporal association with the late fungal development on Arabidopsis leaves. The endoplasmic reticulum-localized proenzyme of AtCEP1 was further visualized at the haustorial complex encased with callose. The AtCPR5 gene (CONSTITUTIVE EXPRESSION OF PR GENES 5) is a regulator of expression of pathogenesis related genes. Loss of AtCPR5 leads to spontaneous expression of chlorotic lesions which was associated with enhanced expression of AtCEP1. We used the atcpr5-2 mutant plants and the atcep1 atcpr5-2 double mutants harboring a non-functional reporter (PCEP1::pre-pro-3xHA-EGFP-KDEL) for visualization of AtCEP1 promoter activity. We found the specific up-regulation of AtCEP1 in direct neighborhood of spreading leaf lesions thus likely representing cells undergoing PCD. Furthermore, we found a strong resistance of atcpr5 mutant plants against infection with E. cruciferarum. Loss of AtCEP1 had no obvious influence on the strong resistance of atcpr5-2 mutant plants against infection with E. cruciferarum. However, the area of necrotic leaf lesions associated with E. cruciferarum colonies was significantly larger in atcpr5-2 as compared to atcep1 atcpr5-2 double mutant plants. The presence of AtCEP1 thus contributes to AtCPR5-controlled PCD at the sites of powdery mildew infection.

Holaphyllamine, a steroid, is able to induce defense responses in Arabidopsis thaliana and increases resistance against bacterial infection.

A chemical screen of plant-derived compounds identified holaphyllamine, a steroid, able to trigger defense responses in Arabidopsis thaliana and improve resistance against the pathogenic bacterium Pseudomonas syringae pv tomato DC3000. A chemical screen of 1600 plant-derived compounds was conducted and allowed the identification of a steroid able to activate defense responses in A. thaliana at a concentration of 1µM without altering growth. The identified compound is holaphyllamine (HPA) whose chemical structure is similar to steroid pregnanes of mammals. Our data show that HPA, which is not constitutively present in A. thaliana, is able to trigger the formation of reactive oxygen species, deposition of callose and expression of several pathogenesis-related genes of the salicylic and jasmonic acid pathways. In addition, the results show that pre-treatment of A. thaliana seedlings with HPA before infection with the pathogenic bacterium Pseudomonas syringae pv tomato DC3000 results in a significant reduction of symptoms (i.e., reduction of bacterial colonies). Using A. thaliana mutants, we have found that the activation of defense responses by HPA does not depend on BRI1/BAK1 receptor kinases. Finally, a structure/function study reveals that the minimal structure required for activity is a 5-pregnen-20-one steroid with an equatorial nucleophilic group in C-3. Together, these findings demonstrate that HPA can activate defense responses that lead to improved resistance against bacterial infection in A. thaliana.

5-Aminolevulinic Acid Dehydratase Gene Dosage Affects Programmed Cell Death and Immunity.

Programmed cell death (PCD) is an important form to protect plants from pathogen attack. However, plants must precisely control the PCD process under microbe attacks to avoid detrimental effects. The complexity of how plants balance the defense activation and PCD requires further clarification. Lesion mimic mutants constitute an excellent material to study the crosstalk between them. Here, we identified a Gossypium hirsutum (cotton) lesion mimic mutant (Ghlmm), which exhibits necrotic leaf damage and enhanced disease resistance. Map-based cloning demonstrated that GhLMMD, encoding 5-aminolevulinic acid dehydratase and located on chromosome D5, was responsible for the phenotype. The mutant was resulted from a nonsense mutation within the coding region of GhLMMD It exhibited an overaccumulation of the 5-aminolevulinic acid, elevated levels of reactive oxygen species and salicylic acid, along with constitutive expression of pathogenesis-related genes and enhanced resistance to the Verticillium dahliae infection. Interestingly, GhLMM plays a dosage-dependent role in regulating PCD of cotton leaves and resistance to V. dahliae infection. This study provides a new strategy on the modulation of plant immunity, particularly in polyploidy plants.

Expression of pathogenesis-related genes in cotton roots in response to Verticillium dahliae PAMP molecules.

Verticillium wilt disease becomes a major threat to many economically important crops. It is unclear whether and how plant immunity takes place during cotton-Verticillium interaction due to the lack of marker genes. Taking advantage of cotton (Gossypium hirsutum) genome, we discovered pathogenesis-related (PR) gene families, which have been widely used as markers of immune responses in plants. To profile the expression of G. hirsutum PR genes in the process of plant immunity, we treated cotton roots with two immunogenic peptides, flg22 and nlp20 known as pathogen-associated molecular patterns, as well as three Verticillium dahliae-derived peptides, nlp20Vd2, nlp23Vd3, and nlp23Vd4 which are highly identical to nlp20. Quantitative real-time PCR results revealed that 14 G. hirsutum PR gene (GhPR) families were induced or suppressed independently in response to flg22, nlp20, nlp20Vd2, nlp23Vd3, and nlp23Vd4. Most GhPR genes are expressed highest at 3 h post incubation of immunogenic peptides. Compared to flg22 and nlp20, nlp20Vd2 is more effective to trigger up-regulated expression of GhPR genes. Notably, both nlp23Vd3 and nlp23Vd4 are able to induce GhPR gene up-regulation, although they do not induce necrosis on cotton leaves. Thus, our results provide marker genes and new immunogenic peptides for further investigation of cotton-V. dahliae interaction.

Gamma irradiation-induced disease resistance of pear (Pyrus pyrifolia “Niitaka”) against Penicillium expansum

In this study, the effects of gamma irradiation on the resistance of pear fruit against Penicillium expansum, the causal agent of blue mould disease, were investigated. A low dose of gamma irradiation for 14 days increased the disease resistance and firmness of pear fruits. Remarkably, exposure to 200 Gy of gamma irradiation significantly maintained fruit firmness, markedly reduced disease incidence and enhanced the activity of defence-related enzymes (e.g., β-1,3-glucanase, phenylalanine ammonia lyase, peroxidase and polyphenol oxidase) and expression of pathogenesis-related (PR) genes (e.g., PR-1, PR-3 and PR-4). Therefore, the gamma irradiation-induced resistance against P. expansum involves both metabolic changes and the induction of expression of defence-related genes. In addition, scanning electron microscopic analysis revealed that gamma irradiation significantly inhibits the growth of P. expansum. These results suggest that exposure of mature harvested pear fruits to artificial gamma irradiation confers fungal disease resistance; therefore, gamma irradiation represents an important strategy for controlling postharvest diseases in pear fruit.

Independent Preharvest Applications of Methyl Jasmonate and Chitosan Elicit Differential Upregulation of Defense-Related Genes with Reduced Incidence of Gray Mold Decay during Postharvest Storage of Fragaria chiloensis Fruit.

The Chilean strawberry (Fragaria chiloensis) fruit has interesting organoleptic properties, but its postharvest life is affected by gray mold decay caused by Botrytis cinerea. The effect of preharvest applications of methyl jasmonate (MeJA) or chitosan on the molecular defense-related responses and protection against gray mold decay were investigated in Chilean strawberry fruit during postharvest storage. Specifically, we inoculated harvested fruit with B. cinerea spores and studied the expression of genes encoding for the pathogenesis-related (PR) proteins β-1,3-glucanases (FcBG2-1, FcBG2-2 and FcBG2-3) and chitinases (FcCHI2-2 and FcCHI3-1), and for polygalacturonase inhibiting proteins (FcPGIP1 and FcPGIP2) at 0, 2, 24, 48, and 72 h post inoculation (hpi). Remarkably, MeJA- and chitosan-treated fruit exhibited a lower incidence of B. cinerea infection than the control-treated at 48 and 72 hpi. At the molecular level, both are efficient elicitors for priming in F. chiloensis fruit since we observed an upregulation of the FcBG2-1, FcBG2-3, FcPGIP1, and FcPGIP2 at 0 hpi. Moreover, a chitosan-mediated upregulation of FcPGIPs at early times post inoculation (2–24 hpi) and MeJA upregulated FcBGs (24–72 hpi) and FcPGIP1 at later times could contribute to reduce B. cinerea incidence by differential upregulation of defense genes. We concluded that preharvest applications of MeJA or chitosan had a long-lasting effect on the reduction of B. cinerea incidence during postharvest as well as an enhancer effect on the induction of PR and PGIP gene expression.

Brachypodium distachyon as alternative model host system for the ergot fungus Claviceps purpurea.

To investigate its susceptibility to ergot infection, we inoculated Brachypodium distachyon with Claviceps purpurea and compared the infection symptoms with those on rye (Secale cereale). We showed that, after inoculation of Brachypodium with Claviceps, the same disease symptoms occurred in comparable temporal and spatial patterns to those on rye. The infection rate of Claviceps on this host was reduced compared with rye, but the disease could be surveyed by fungal genomic DNA quantification. Mutants of Claviceps which were virulence attenuated on rye were also affected on Brachypodium. We were able to show that pathogenesis-related gene expression changed in a typical manner for biotrophic pathogen attack. Our results indicated that the Claviceps-Brachypodium interaction was dependent on salicylic acid, cytokinin and auxin. We consider Brachypodium to be a suitable and useful alternative host; the increased sensitivity compared with rye will be valuable for the identification of infection mechanisms. Future progess in understanding the Claviceps-plant interaction will be facilitated by the use of a well-characterized model host system.

TaPIMP2, a pathogen-induced MYB protein in wheat, contributes to host resistance to common root rot caused by Bipolaris sorokiniana

MYB transcription factors (TFs) have been implicated in various biology processes in model plants. However, functions of the great majority of MYB TFs in wheat (Triticum aestivum L.) have not been characterized. The soil-borne fungal pathogens Bipolaris sorokiniana and Rhizoctonia cerealis are the causal agents of important destructive diseases of wheat. Here, the TaPIMP2 gene, encoding a pathogen-induced MYB protein in wheat, was isolated through comparative transcriptomic analysis, and its defensive role was studied. TaPIMP2 was proved to localize in nuclei. TaPIMP2 responded in a different extent and speed upon infections of B. sorokiniana or R. cerealis. TaPIMP2 displayed different expression patterns after exogenous application of phytohormones, including abscisic acid, ethylene, and salicylic acid. Silencing of TaPIMP2 repressed resistance of wheat cultivar Yangmai 6 to B. sorokiniana, but did not alter resistance of wheat line CI12633 to R. cerealis. TaPIMP2 overexpression significantly improved resistance to B. sorokiniana rather than R. cerealis in transgenic wheat. Moreover, TaPIMP2 positively modulated the expression of pathogenesis-related genes, including PR1a, PR2, PR5, and PR10. Collectively, TaPIMP2 positively contributes to wheat resistance to B. sorokiniana possibly through regulating the expression of defense-related genes, and TaPIMP2 plays distinct roles in defense responses to different fungal infection.

The Elongator complex‐associated protein DRL1 plays a positive role in immune responses against necrotrophic fungal pathogens in Arabidopsis

DEFORMED ROOT AND LEAVES1 (DRL1) is an Arabidopsis homologue of the yeast TOXIN TARGET4 (TOT4)/KILLER TOXIN-INSENSITIVE12 (KTI12) protein that is physically associated with the RNA polymerase II-interacting protein complex named Elongator. Mutations in DRL1 and Elongator lead to similar morphological and molecular phenotypes, suggesting that DRL1 and Elongator may functionally overlap in Arabidopsis. We have shown previously that Elongator plays an important role in both salicylic acid (SA)- and jasmonic acid (JA)/ethylene (ET)-mediated defence responses. Here, we tested whether DRL1 also plays a similar role as Elongator in plant immune responses. Our results show that, although DRL1 partially contributes to SA-induced cytotoxicity, it does not play a significant role in SA-mediated expression of PATHOGENESIS-RELATED genes and resistance to the virulent bacterial pathogen Pseudomonas syringae pv. maculicola ES4326. In contrast, DRL1 is required for JA/ET- and necrotrophic fungal pathogen Botrytis cinerea-induced defence gene expression and for resistance to B.cinerea and Alternaria brassicicola. Furthermore, unlike the TOT4/KTI12 gene which, when overexpressed in yeast, confers zymocin resistance, a phenotype of the tot4/kti12 mutant, overexpression of DRL1 does not change B.cinerea-induced defence gene expression and resistance to this pathogen. Finally, DRL1 contains an N-terminal P-loop and a C-terminal calmodulin (CaM)-binding domain and is a CaM-binding protein. We demonstrate that both the P-loop and the CaM-binding domain are essential for the function of DRL1 in B.cinerea-induced expression of PDF1.2 and ORA59, and in resistance to B.cinerea, suggesting that the function of DRL1 in plant immunity may be regulated by ATP/GTP and CaM binding.

OsCUL3a Negatively Regulates Cell Death and Immunity by Degrading OsNPR1 in Rice.

Cullin3-based RING E3 ubiquitin ligases (CRL3), composed of Cullin3 (CUL3), RBX1, and BTB proteins, are involved in plant immunity, but the function of CUL3 in the process is largely unknown. Here, we show that rice (Oryza sativa) OsCUL3a is important for the regulation of cell death and immunity. The rice lesion mimic mutant oscul3a displays a significant increase in the accumulation of flg22- and chitin-induced reactive oxygen species, and in pathogenesis-related gene expression as well as resistance to Magnaporthe oryzae and Xanthomonas oryzae pv oryzae. We cloned the OsCUL3a gene via a map-based strategy and found that the lesion mimic phenotype of oscul3a is associated with the early termination of OsCUL3a protein. Interaction assays showed that OsCUL3a interacts with both OsRBX1a and OsRBX1b to form a multisubunit CRL in rice. Strikingly, OsCUL3a interacts with and degrades OsNPR1, which acts as a positive regulator of cell death in rice. Accumulation of OsNPR1 protein is greater in the oscul3a mutant than in the wild type. Furthermore, the oscul3a osnpr1 double mutant does not exhibit the lesion mimic phenotype of the oscul3a mutant. Our data demonstrate that OsCUL3a negatively regulates cell death and immunity by degrading OsNPR1 in rice.

Graft-transmissible resistance of cherry pepper (Capsicum annuum var. cerasiforme) to powdery mildew (Leveillula taurica) is associated with elevated superoxide accumulation, NADPH oxidase activity and pathogenesis-related gene expression

We found that resistance to pepper powdery mildew (PM) (Leveillula taurica) develops in a sweet pepper (Capsicum annuum) cultivar (‘Total’) when grafted on a resistant cherry pepper (C. annuum var. cerasiforme) rootstock (cv. Szentesi). Resistance is manifested both towards PM symptoms and pathogen accumulation. In healthy, uninfected plants PM-resistance can be predicted by enhanced accumulation of the reactive oxygen species (ROS) superoxide (O 2 ) and activity of NADPH oxidase, the enzyme mainly responsible for pathogenesis-related superoxide generation. In L. taurica-inoculated PM-resistant ‘Szentesi’ high levels of superoxide and NADPH oxidase activity are sustained even 45 days after inoculation, as opposed to PM-susceptible ‘Total’. This is also true for ‘Total’ grafted on resistant ‘Szentesi’ rootstocks, where PM resistance, enhanced superoxide production and NADPH oxidase activity is likely due to an unknown, graft-transmitted signal. To further elucidate the mechanisms of graft-transmissible PM-resistance we monitored expression of pathogenesis-related (PR) genes in healthy and infected plants. In healthy plants, expression of CaPR-1 is several times higher in leaves of PM-resistant pepper than in sensitive plants, while high expression of CaPR-2 (glucanase) does not entirely correlate with PM-resistance, being detectable only in PM-resistant ‘Szentesi’. However, during advanced stages of PM-pathogenesis (45 DAI) expression of CaPR-1 and CaPR-2 is by far the highest in PM-susceptible ‘Total’. Our results suggest that the direct biochemical cause of graft-transmissible PM-resistance in pepper is the enhanced accumulation of NADPH oxidase-generated superoxide. To our knowledge, this is the first report on the role of ROS (superoxide) in graft-transmissible, pathogen-specific disease resistance.

A Conserved Puccinia striiformis Protein Interacts with Wheat NPR1 and Reduces Induction of Pathogenesis-Related Genes in Response to Pathogens.

In Arabidopsis, NPR1 is a key transcriptional coregulator of systemic acquired resistance. Upon pathogen challenge, NPR1 translocates from the cytoplasm to the nucleus, in which it interacts with TGA-bZIP transcription factors to activate the expression of several pathogenesis-related (PR) genes. In a screen of a yeast two-hybrid library from wheat leaves infected with Puccinia striiformis f. sp. tritici, we identified a conserved rust protein that interacts with wheat NPR1 and named it PNPi (for Puccinia NPR1 interactor). PNPi interacts with the NPR1/NIM1-like domain of NPR1 via its C-terminal DPBB_1 domain. Using bimolecular fluorescence complementation assays, we detected the interaction between PNPi and wheat NPR1 in the nucleus of Nicotiana benthamiana protoplasts. A yeast three-hybrid assay showed that PNPi interaction with NPR1 competes with the interaction between wheat NPR1 and TGA2.2. In barley transgenic lines overexpressing PNPi, we observed reduced induction of multiple PR genes in the region adjacent to Pseudomonas syringae pv. tomato DC3000 infection. Based on these results, we hypothesize that PNPi has a role in manipulating wheat defense response via its interactions with NPR1.

Overexpression of soybean GmERF9 enhances the tolerance to drought and cold in the transgenic tobacco

Ethylene response factors (ERFs) are widespread in plants, which are widely involved in plant response to biotic and abiotic stress. In this research, a soybean gene, GmERF9, was identified and the function was characterized. The results showed that GmERF9 contained a typical AP2/ERF binding domain and a putative nuclear localization signal sequence. The real-time fluorescence quantitative PCR (qPCR) revealed that the expression of GmERF9 could be induced by ethylene (ET), abscisic acid (ABA), drought, salt and cold stresses. GmERF9 protein could specifically bind to the GCC-box and activate the expression of the reporter gene in the yeast cells and tobacco leaves. Overexpression of GmERF9 enhanced the expression of pathogenesis-related (PR) genes, including PR1, PR2, Osmotin (PR5), and SAR8.2. Also, the overexpression of GmERF9 increased the accumulation of proline and soluble carbohydrate, and decreased the accumulation of malondialdehyde under drought and cold stresses in the transgenic tobacco compared to the wild type (WT) tobacco, which indicated that GmERF9 enhanced the tolerance to drought and cold stresses in the transgenic tobacco. In summary, the function of GmERF9 is involved in the response to environmental stresses for plants, which can be used as a candidate gene for genetic engineering of crops.

Identification of Methylosome Components as Negative Regulators of Plant Immunity Using Chemical Genetics

Nucleotide-binding leucine-rich repeat (NLR) proteins serve as immune receptors in both plants and animals. To identify components required for NLR-mediated immunity, we designed and carried out a chemical genetics screen to search for small molecules that can alter immune responses in Arabidopsis thaliana. From 13 600 compounds, we identified Ro 8-4304 that was able to specifically suppress the severe autoimmune phenotypes of chs3-2D (chilling sensitive 3, 2D), including the arrested growth morphology and heightened PR (Pathogenesis Related) gene expression. Further, six Ro 8-4304 insensitive mutants were uncovered from the Ro 8-4304-insensitive mutant (rim) screen using a mutagenized chs3-2D population. Positional cloning revealed that rim1 encodes an allele of AtICln (I, currents; Cl, chloride; n, nucleotide). Genetic and biochemical analysis demonstrated that AtICln is in the same protein complex with the methylosome components small nuclear ribonucleoprotein D3b (SmD3b) and protein arginine methyltransferase 5 (PRMT5), which are required for the biogenesis of small nuclear ribonucleoproteins (snRNPs) involved in mRNA splicing. Double mutant analysis revealed that SmD3b is also involved in the sensitivity to Ro 8-4304, and the prmt5-1 chs3-2D double mutant is lethal. Loss of AtICln, SmD3b, or PRMT5 function results in enhanced disease resistance against the virulent oomycete pathogen Hyaloperonospora arabidopsidis Noco2, suggesting that mRNA splicing plays a previously unknown negative role in plant immunity. The successful implementation of a high-throughput chemical genetic screen and the identification of a small-molecule compound affecting plant immunity indicate that chemical genetics is a powerful tool to study whole-organism plant defense pathways.

Salicylic acid to decrease plant stress

Pollution and climate change degrade plant health. Plant stress can be decreased by application of salicylic acid, an hormone involved in plant signaling. Salicylic acid indeed initiates pathogenesis-related gene expression and synthesis of defensive compounds involved in local resistance and systemic acquired resistance. Salicylic acid may thus be used against pathogen virulence, heavy metal stresses, salt stress, and toxicities of other elements. Applied salicylic acid improves photosynthesis, growth, and various other physiological and biochemical characteristics in stressed plants. Salicylic acid antagonizes the oxidative damaging effect of metal toxicity directly by acting as an antioxidant to scavenge the reactive oxygen species and by activating the antioxidant systems of plants and indirectly by reducing uptake of metals from their medium of growth. We review here the use of exogenous salicylic acid in alleviating bacterial, fungal, and viral diseases, heavy metal toxicity, toxicity of essential micronutrients, and salt stress.

Application of Glycerol for Induced Powdery Mildew Resistance in Triticum aestivum L.

Previous work has demonstrated that glycerol-3-phosphate (G3P) and oleic acid (18:1) are two important signal molecules associated with plant resistance to fungi. In this article, we provide evidence that a 3% glycerol spray application 1–2 days before powdery mildew infection and subsequent applications once every 4 days was sufficient to stimulate the plant defense responses without causing any significant damage to wheat leaves. We found that G3P and oleic acid levels were markedly induced by powdery mildew infection. In addition, TaGLI1 (encoding a glycerol kinase) and TaSSI2 (encoding a stearoylacyl carrier protein fatty acid desaturase), two genes associated with the glycerol and fatty acid (FA) pathways, respectively, were induced by powdery mildew infection, and their promoter regions contain some fungal response elements. Moreover, exogenous application of glycerol increased the G3P level and decreased the level of oleic acid (18:1). Glycerol application induced the expression of pathogenesis-related (PR) genes (TaPR-1, TaPR-2, TaPR-3, TaPR-4, and TaPR-5), induced the generation of reactive oxygen species (ROS) before powdery mildew infection, and induced salicylic acid (SA) accumulation in wheat leaves. Further, we sprayed glycerol in a wheat field and found that it significantly (p < 0.05) reduced the severity of powdery mildew disease and lessened disease-associated kernel weight loss, all without causing any noticeable degradation in wheat seed quality.

Signal molecules involved in the regulation of the wheat defense response to Septoria nodorum infection

The response of Triticum aestivum L. to infection by Septoria nodorum Berk, a pathogen causing speckled leaf blotch, was studied. The effect of salicylic acid (SA) and jasmonic acid (JA) signal molecules, as well as chitooligosaccharides (COSs) with different acetylation degrees (ADs), on the accumulation of hydrogen peroxide (Н2О2) in wheat leaves and the pathogenesis-related (PR) proteins of oxalate oxidase (AJ556991.1), peroxidase (TC 151917), and proteinase inhibitor (EU293132.1) was investigated. Treatment with the signal molecules inhibited S. nodorum growth and stimulated Н2О2 accumulation, as well as PR gene expression. SA and COS with 65% AD are found to be more efficient in Н2О2 induction and elevation of the transcriptional level of the oxalate oxidase and peroxidase genes. At the same time, JA and COS with 30% AD stimulated transcription of the proteinase inhibitor gene. The results suggest the existence of differential means of defense response induction by signal molecules with more prospects for the regulation of plant immunity.

Effect of β-aminobutyric acid on resistance of tomato against Pectobacterium carotovorum subsp. carotovorum

Stem rot of tomato caused by Pectobacterium carotovorum subsp. carotovorum (Pcc) results in economic yield loss worldwide. Previous studies have demonstrated the role of β-aminobutyric acid (BABA) in control of numerous plant diseases. To extend our understanding for the efficacy of BABA as an inducer agent against plant diseases, we evaluated the effect of BABA on disease severity of stem rot during infection of tomato by Pcc. BABA at concentration of 200 µM reduced the disease severity and offered protection against Pcc. On the other hand, BABA did not have direct antibacterial effect in vitro. Furthermore, we examined the effects of BABA on expression of pathogenesis-related gene 1 (PR-1), pathogenesis-related gene 2 (PR-2), phenylalanine ammonia-lyase (PAL) and catalase (CAT). Pretreatment with BABA led to more expression of PR-1 and PR-2 after Pcc infection when compared with their counterparts pretreated with water (control). PR-1 expression in BABA/Pcc treatment increased 2.83-, 4.31-, 2.46- and 1.88-fold at 24, 48, 72 and 96 h postpathogen inoculation (hpi), respectively, compared to water/Pcc treatment. Moreover, PR-2 expression in BABA/Pcc treatment increased 2.66-, 3.43-, 2.19- and 1.91-fold at 24, 48, 72 and 96 hpi, respectively, compared to water/Pcc treatment. On the other hand, PAL expression was transient during enhanced resistance by BABA. In comparison with water/Pcc treatment, PAL expression enhanced 2.42-fold at 24 hpi in BABA/Pcc treatment, whereas PAL expression was remained unchanged at 48, 72 and 96 hpi. CAT expression increased in early stages of the resistance induced by BABA. In BABA/Pcc treatment, CAT expression enhanced 4.6- and 3.1-fold at 24 and 48 hpi, respectively, compared to water/Pcc treatment. Our data confirmed the role of BABA as an effective resistance inducer against Pcc that might be considered in integrated diseases management programs.

The Xanthomonas campestris pv. vesicatoria Type-3 Effector XopB Inhibits Plant Defence Responses by Interfering with ROS Production.

The bacterial pathogen Xanthomonas campestris pv. vesicatoria 85–10 (Xcv) translocates about 30 type-3 effector proteins (T3Es) into pepper plants (Capsicum annuum) to suppress plant immune responses. Among them is XopB which interferes with PTI, ETI and sugar-mediated defence responses, but the underlying molecular mechanisms and direct targets are unknown so far. Here, we examined the XopB-mediated suppression of plant defence responses in more detail. Infection of susceptible pepper plants with Xcv lacking xopB resulted in delayed symptom development compared to Xcv wild type infection concomitant with an increased formation of salicylic acid (SA) and expression of pathogenesis-related (PR) genes. Expression of xopB in Arabidopsis thaliana promoted the growth of the virulent Pseudomonas syringae pv. tomato (Pst) DC3000 strain. This was paralleled by a decreased SA-pool and a lower induction of SA-dependent PR gene expression. The expression pattern of early flg22-responsive marker genes indicated that MAPK signalling was not altered in the presence of XopB. However, XopB inhibited the flg22-triggered burst of reactive oxygen species (ROS). Consequently, the transcript accumulation of AtOXI1, a ROS-dependent marker gene, was reduced in xopB-expressing Arabidopsis plants as well as callose deposition. The lower ROS production correlated with a low level of basal and flg22-triggered expression of apoplastic peroxidases and the NADPH oxidase RBOHD. Conversely, deletion of xopB in Xcv caused a higher production of ROS in leaves of susceptible pepper plants. Together our results demonstrate that XopB modulates ROS responses and might thereby compromise plant defence.