jasmonic-acid and benzo-1-2-3-thiadiazole

Salicylic acid (SA), an essential secondary messenger for plant defence responses, plays a role in maintaining a balance (trade-off) between plant growth and resistance induction, but the detailed mechanism has not been explored. Because the SA mimic benzothiadiazole (BTH) is a more stable inducer of plant defence than SA after exogenous application, we analysed expression profiles of defence genes after BTH treatment to better understand SA-mediated immune induction. Transcript levels of the salicylic acid glucosyltransferase (SAGT) gene were significantly lower in BTH-treated Nicotiana tabacum (Nt) plants than in SA-treated Nt control plants, suggesting that SAGT may play an important role in SA-related host defence responses. Treatment with BTH followed by SA suppressed SAGT transcription, indicating that the inhibitory effect of BTH is not reversible. In addition, in BTH-treated Nt and Nicotiana benthamiana (Nb) plants, an early high accumulation of SA and SA 2-O-β-d-glucoside was only transient compared to the control. This observation agreed well with the finding that SAGT-overexpressing (OE) Nb lines contained less SA and jasmonic acid (JA) than in the Nb plants. When inoculated with a virus, the OE Nb plants showed more severe symptoms and accumulated higher levels of virus, while resistance increased in SAGT-silenced (IR) Nb plants. In addition, the IR plants restricted bacterial spread to the inoculated leaves. After the BTH treatment, OE Nb plants were slightly larger than the Nb plants. These results together indicate that SAGT has a pivotal role in the balance between plant growth and SA/JA-mediated defence for optimum plant fitness.

Topics: Cyclopentanes; Disease Resistance; Gene Expression Regulation, Plant; Glucosyltransferases; Nicotiana; Oxylipins; Plant Diseases; Plant Leaves; Salicylic Acid; Thiadiazoles

Plant defense inducers that mimic functions of the plant immune hormone salicylic acid (SA) often affect plant growth. Although benzothiadiazole (BTH), a synthetic analog of SA, has been widely used to protect crops from diseases by inducing plant defense responses, we recently demonstrated that SA, but not BTH, confers resistance against Rhizoctonia solani, the causal agent of sheath blight disease, in Brachypodium distachyon. Here, we demonstrated that BTH compromised the resistance of Bd3-1 and Gaz4, the two sheath blight-resistant accessions of B. distachyon, which activate SA-dependent signaling following challenge by R. solani. Moreover, upon analyzing our published RNA-seq data from B. distachyon treated with SA or BTH, we found that BTH specifically induces expression of genes related to chloroplast function and jasmonic acid (JA) signaling, suggesting that BTH attenuates R. solani resistance by perturbing growth-defense trade-offs and/or by inducing a JA response that may increase susceptibility to R. solani. Our findings demonstrated that BTH does not work as a simple mimic of SA in B. distachyon, and consequently may presumably cause unfavorable side effects through the transcriptional alteration, particularly with respect to R. solani resistance.

Topics: Brachypodium; Cyclopentanes; Gene Expression Regulation, Plant; Oxylipins; Plant Diseases; Plant Growth Regulators; Plant Leaves; Plant Proteins; Rhizoctonia; Salicylic Acid; Thiadiazoles

Necrotrophic and biotrophic pathogens are resisted by different plant defenses. While necrotrophic pathogens are sensitive to jasmonic acid (JA)-dependent resistance, biotrophic pathogens are resisted by salicylic acid (SA)- and reactive oxygen species (ROS)-dependent resistance. Although many pathogens switch from biotrophy to necrotrophy during infection, little is known about the signals triggering this transition. This study is based on the observation that the early colonization pattern and symptom development by the ascomycete pathogen Plectosphaerella cucumerina (P. cucumerina) vary between inoculation methods. Using the Arabidopsis (Arabidopsis thaliana) defense response as a proxy for infection strategy, we examined whether P. cucumerina alternates between hemibiotrophic and necrotrophic lifestyles, depending on initial spore density and distribution on the leaf surface. Untargeted metabolome analysis revealed profound differences in metabolic defense signatures upon different inoculation methods. Quantification of JA and SA, marker gene expression, and cell death confirmed that infection from high spore densities activates JA-dependent defenses with excessive cell death, while infection from low spore densities induces SA-dependent defenses with lower levels of cell death. Phenotyping of Arabidopsis mutants in JA, SA, and ROS signaling confirmed that P. cucumerina is differentially resisted by JA- and SA/ROS-dependent defenses, depending on initial spore density and distribution on the leaf. Furthermore, in situ staining for early callose deposition at the infection sites revealed that necrotrophy by P. cucumerina is associated with elevated host defense. We conclude that P. cucumerina adapts to early-acting plant defenses by switching from a hemibiotrophic to a necrotrophic infection program, thereby gaining an advantage of immunity-related cell death in the host.

Topics: Arabidopsis; Ascomycota; Cell Death; Cyclopentanes; Disease Resistance; Metabolic Networks and Pathways; Metabolome; Metabolomics; Models, Biological; Oxylipins; Phenotype; Plant Diseases; Plant Leaves; Reactive Oxygen Species; Salicylic Acid; Spores, Fungal; Thiadiazoles

The root hemiparasite witchweed (Striga spp.) is a devastating agricultural pest that causes losses of up to $1 billion US annually in sub-Saharan Africa. Development of resistant crops is one of the cost-effective ways to address this problem. However, the molecular mechanisms underlying resistance are not well understood. To understand molecular events upon Striga spp. infection, we conducted genome-scale RNA sequencing expression analysis using Striga hermonthica-infected rice (Oryza sativa) roots. We found that transcripts grouped under the Gene Ontology term defense response were significantly enriched in up-regulated differentially expressed genes. In particular, we found that both jasmonic acid (JA) and salicylic acid (SA) pathways were induced, but the induction of the JA pathway preceded that of the SA pathway. Foliar application of JA resulted in higher resistance. The hebiba mutant plants, which lack the JA biosynthesis gene allene oxide cyclase, exhibited severe S. hermonthica susceptibility. The resistant phenotype was recovered by application of JA. By contrast, the SA-deficient NahG rice plants were resistant against S. hermonthica, indicating that endogenous SA is not required for resistance. However, knocking down WRKY45, a regulator of the SA/benzothiadiazole pathway, resulted in enhanced susceptibility. Interestingly, NahG plants induced the JA pathway, which was down-regulated in WRKY45-knockdown plants, linking the resistant and susceptible phenotypes to the JA pathway. Consistently, the susceptibility phenotype in the WRKY45-knockdown plants was recovered by foliar JA application. These results point to a model in which WRKY45 modulates a cross talk in resistance against S. hermonthica by positively regulating both SA/benzothiadiazole and JA pathways.

Topics: Cyclopentanes; Disease Resistance; Down-Regulation; Ethylenes; Gene Expression Profiling; Gene Expression Regulation, Plant; Genes, Plant; Models, Biological; Mutation; Oryza; Oxylipins; Plant Diseases; Plant Proteins; RNA, Messenger; Salicylic Acid; Signal Transduction; Striga; Thiadiazoles

Feeding by insect herbivores activates plant signaling pathways, resulting in the enhanced production of secondary metabolites and other resistance-related traits by injured plants. These traits can reduce insect fitness, deter feeding, and attract beneficial insects. Organic and inorganic chemicals applied as a foliar spray, seed treatment, or soil drench can activate these plant responses. Azelaic acid (AA), benzothiadiazole (BTH), gibberellic acid (GA), harpin, and jasmonic acid (JA) are thought to directly mediate plant responses to pathogens and herbivores or to mimic compounds that do. The effects of these potential elicitors on the induction of plant defenses were determined by measuring the weight gains of fall armyworm, Spodoptera frugiperda (J. E. Smith) (FAW) (Lepidoptera: Noctuidae) larvae on four crop plants, cotton, corn, rice, and soybean, treated with the compounds under greenhouse conditions. Treatment with JA consistently reduced growth of FAW reared on treated cotton and soybean. In contrast, FAW fed BTH- and harpin-treated cotton and soybean tissue gained more weight than those fed control leaf tissue, consistent with negative crosstalk between the salicylic acid and JA signaling pathways. No induction or inconsistent induction of resistance was observed in corn and rice. Follow-up experiments showed that the co-application of adjuvants with JA failed to increase the effectiveness of induction by JA and that soybean looper [Chrysodeixis includens (Walker)], a relative specialist on legumes, was less affected by JA-induced responses in soybean than was the polyphagous FAW. Overall, the results of these experiments demonstrate that the effectiveness of elicitors as a management tactic will depend strongly on the identities of the crop, the pest, and the elicitor involved.

Topics: Animals; Crops, Agricultural; Cyclopentanes; Dicarboxylic Acids; Disease Resistance; Gibberellins; Glycine max; Gossypium; Herbivory; Oryza; Oxylipins; Spodoptera; Thiadiazoles; Zea mays

Gray mold (Botrytis cinerea) is an important disease of tomato (Solanum lycopersicum). This study examined defense-related gene expression involved in the resistance to B. cinerea that is induced in tomato plants by benzothiadiazole and Trichoderma harzianum T39 soil drench. In whole plants, transcriptional changes related to salicylic acid and ethylene were induced by the application of a 0.01% benzothiadiazole solution, whereas changes related to jasmonic acid were induced by the application of a 0.4% T39 suspension. On detached leaves, soil treatment by T39 led to enhanced resistance to B. cinerea infection that was proportional to the concentration of the T39 suspension. By 5 days after pathogen inoculation, the plants that had received the 0.04% T39 drench exhibited 62% less severe disease than the untreated plants. The 0.4% T39 drench led to an 84% reduction in disease severity. Observations of B. cinerea infection in leaves harvested from plants grown in the treated soils revealed that drenching with a T39 suspension induces systemic resistance against B. cinerea and primes salicylic acid- and ethylene-related gene expression in a manner proportional to the concentration of the biocontrol agent. Benzothiadiazole treatment induced resistance to gray mold independently of salicylic acid and led to strong priming of two genes known to be involved in defense against B. cinerea, Pti5 and PI2.

Topics: Botrytis; Cyclopentanes; Disease Resistance; Ethylenes; Gene Expression Regulation, Plant; Oxylipins; Plant Diseases; Plant Growth Regulators; Plant Leaves; Plant Proteins; RNA, Messenger; RNA, Plant; Salicylic Acid; Solanum lycopersicum; Thiadiazoles; Trichoderma

Incorporation of plant defense activators is an innovative approach to development of an integrated strategy for the management of turfgrass diseases. The effects of salicylic acid (SA), benzothiadiazole (BTH, chemical analog of SA), jasmonic acid (JA), and ethephon (ET, an ethylene-releasing compound) on development of gray leaf spot in perennial ryegrass (Lolium perenne L.) caused by Magnaporthe oryzae were evaluated. Gray leaf spot disease incidence and severity were significantly decreased when plants were treated prior to inoculation with SA, BTH, and partially by ET but not by JA. Accumulation of endogenous SA and elevated expression of pathogenesis-related (PR)-1, PR-3.1, and PR-5 genes were associated with inoculation of plants by M. oryzae. Treatment of plants with SA enhanced expression levels of PR-3.1 and PR-5 but did not affect the PR-1 level, whereas BTH treatment enhanced relative expression levels of all three PR genes. Microscopic observations of leaves inoculated with M. oryzae revealed higher frequencies of callose deposition at the penetration sites in SA- and BTH-treated plants compared with the control plants (treated with water). These results suggest that early and higher induction of these genes by systemic resistance inducers may provide perennial ryegrass with a substantial advantage to defend against infection by M. oryzae.

Topics: Cyclopentanes; Ethylenes; Gene Expression Regulation, Plant; Glucans; Lolium; Magnaporthe; Organophosphorus Compounds; Oxylipins; Plant Diseases; Plant Growth Regulators; Plant Immunity; Plant Leaves; Plant Proteins; RNA, Plant; Salicylic Acid; Thiadiazoles

Systemically induced resistance is a promising strategy to control plant diseases, as it affects numerous pathogens. However, since induced resistance reduces one or both growth and activity of plant pathogens, the indigenous microflora may also be affected by an enhanced defensive state of the plant. The aim of this study was to elucidate how much the bacterial rhizosphere microflora of Arabidopsis is affected by induced systemic resistance (ISR) or systemic acquired resistance (SAR). Therefore, the bacterial microflora of wild-type plants and plants affected in their defense signaling was compared. Additionally, ISR was induced by application of methyl jasmonate and SAR by treatment with salicylic acid or benzothiadiazole. As a comparative model, we also used wild type and ethylene-insensitive tobacco. Some of the Arabidopsis genotypes affected in defense signaling showed altered numbers of culturable bacteria in their rhizospheres; however, effects were dependent on soil type. Effects of plant genotype on rhizosphere bacterial community structure could not be related to plant defense because chemical activation of ISR or SAR had no significant effects on density and structure of the rhizosphere bacterial community. These findings support the notion that control of plant diseases by elicitation of systemic resistance will not significantly affect the resident soil bacterial microflora.

Topics: Anti-Infective Agents; Arabidopsis; Arabidopsis Proteins; Bacteria; Biota; Cyclopentanes; Ethylenes; Gene Expression Regulation, Plant; Mutation; Nicotiana; Oxylipins; Plant Growth Regulators; Plant Immunity; Pseudomonas; Rhizosphere; Salicylic Acid; Signal Transduction; Thiadiazoles

The priming agent β-aminobutyric acid (BABA) is known to enhance Arabidopsis resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 by potentiating salicylic acid (SA) defence signalling, notably PR1 expression. The molecular mechanisms underlying this phenomenon remain unknown. A genome-wide microarray analysis of BABA priming during Pst DC3000 infection revealed direct and primed up-regulation of genes that are responsive to SA, the SA analogue benzothiadiazole and pathogens. In addition, BABA was found to inhibit the Arabidopsis response to the bacterial effector coronatine (COR). COR is known to promote bacterial virulence by inducing the jasmonic acid (JA) response to antagonize SA signalling activation. BABA specifically repressed the JA response induced by COR without affecting other plant JA responses. This repression was largely SA-independent, suggesting that it is not caused by negative cross-talk between SA and JA signalling cascades. Treatment with relatively high concentrations of purified COR counteracted BABA inhibition. Under these conditions, BABA failed to protect Arabidopsis against Pst DC3000. BABA did not induce priming and resistance in plants inoculated with a COR-deficient strain of Pst DC3000 or in the COR-insensitive mutant coi1-16. In addition, BABA blocked the COR-dependent re-opening of stomata during Pst DC3000 infection. Our data suggest that BABA primes for enhanced resistance to Pst DC3000 by interfering with the bacterial suppression of Arabidopsis SA-dependent defences. This study also suggests the existence of a signalling node that distinguishes COR from other JA responses.

Topics: Amino Acids; Aminobutyrates; Arabidopsis; Bacterial Toxins; Cyclopentanes; Gene Expression Profiling; Gene Expression Regulation, Plant; Genes, Plant; Indenes; Mutation; Oligonucleotide Array Sequence Analysis; Oxylipins; Plant Diseases; Plant Immunity; Plant Stomata; Plants, Genetically Modified; Pseudomonas syringae; Salicylic Acid; Signal Transduction; Thiadiazoles; Up-Regulation

Complex defense signaling pathways, controlled by different hormones, are involved in the reaction of plants to a wide range of biotic and abiotic stress factors. We studied the ability of salicylic acid, jasmonate (JA), and ethylene (ET) to induce systemic defense in rice (Oryza sativa) against the root knot nematode Meloidogyne graminicola. Exogenous ET (ethephon) and JA (methyl jasmonate) supply on the shoots induced a strong systemic defense response in the roots, exemplified by a major up-regulation of pathogenesis-related genes OsPR1a and OsPR1b, while the salicylic acid analog BTH (benzo-1,2,3-thiadiazole-7-carbothioic acid S-methyl ester) was a less potent systemic defense inducer from shoot to root. Experiments with JA biosynthesis mutants and ET-insensitive transgenics showed that ET-induced defense requires an intact JA pathway, while JA-induced defense was still functional when ET signaling was impaired. Pharmacological inhibition of JA and ET biosynthesis confirmed that JA biosynthesis is needed for ET-induced systemic defense, and quantitative real-time reverse transcription-polymerase chain reaction data revealed that ET application onto the shoots strongly activates JA biosynthesis and signaling genes in the roots. All data provided in this study point to the JA pathway to play a pivotal role in rice defense against root knot nematodes. The expression of defense-related genes was monitored in root galls caused by M. graminicola. Different analyzed defense genes were attenuated in root galls caused by the nematode at early time points after infection. However, when the exogenous defense inducers ethephon and methyl jasmonate were supplied to the plant, the nematode was less effective in counteracting root defense pathways, hence making the plant more resistant to nematode infection.

Topics: Animals; Cyclopentanes; Nematoda; Organophosphorus Compounds; Oryza; Oxylipins; Plant Roots; Thiadiazoles

Herbivore-induced plant volatiles affect the systemic response of plants to local damage and hence represent potential plant hormones. These signals can also lead to "plant-plant communication," a defense induction in yet undamaged plants growing close to damaged neighbors. We observed this phenomenon in the context of disease resistance. Lima bean (Phaseolus lunatus) plants in a natural population became more resistant against a bacterial pathogen, Pseudomonas syringae pv syringae, when located close to conspecific neighbors in which systemic acquired resistance to pathogens had been chemically induced with benzothiadiazole (BTH). Airborne disease resistance induction could also be triggered biologically by infection with avirulent P. syringae. Challenge inoculation after exposure to induced and noninduced plants revealed that the air coming from induced plants mainly primed resistance, since expression of PATHOGENESIS-RELATED PROTEIN2 (PR-2) was significantly stronger in exposed than in nonexposed individuals when the plants were subsequently challenged by P. syringae. Among others, the plant-derived volatile nonanal was present in the headspace of BTH-treated plants and significantly enhanced PR-2 expression in the exposed plants, resulting in reduced symptom appearance. Negative effects on growth of BTH-treated plants, which usually occur as a consequence of the high costs of direct resistance induction, were not observed in volatile organic compound-exposed plants. Volatile-mediated priming appears to be a highly attractive means for the tailoring of systemic acquired resistance against plant pathogens.

Topics: Air; Cyclopentanes; Fabaceae; Immunity, Innate; Oxylipins; Plant Diseases; Plant Proteins; Pseudomonas syringae; Signal Transduction; Thiadiazoles; Volatile Organic Compounds

RING finger proteins comprise a large family and play key roles in regulating growth/developmental processes, hormone signaling and responses to biotic and abiotic stresses in plants. A rice gene, OsBIRF1, encoding a putative RING-H2 finger protein, was cloned and identified. OsBIRF1 encodes a 396 amino acid protein belonging to the ATL family characterized by a conserved RING-H2 finger domain (C-X2-C-X15-C-X1-H-X2-H-X2-C-X10-C-X2-C), a transmembrane domain at the N-terminal, a basic amino acid rich region and a characteristic GLD region. Expression of OsBIRF1 was up-regulated in rice seedlings after treatment with benzothaidiazole, salicylic acid, l-aminocyclopropane-1-carboxylic acid and jasmonic acid, and was induced differentially in incompatible but not compatible interactions between rice and Magnaporthe grisea, the causal agent of blast disease. Transgenic tobacco plants that constitutively express OsBIRF1 exhibit enhanced disease resistance against tobacco mosaic virus and Pseudomonas syringae pv. tabaci and elevated expression levels of defense-related genes, e.g. PR-1, PR-2, PR-3 and PR-5. The OsBIRF1-overexpressing transgenic tobacco plants show increased oxidative stress tolerance to exogenous treatment with methyl viologen and H2O2, and up-regulate expression of oxidative stress-related genes. Reduced ABA sensitivity in root elongation and increased drought tolerance in seed germination were also observed in OsBIRF1 transgenic tobacco plants. Furthermore, the transgenic tobacco plants show longer roots and higher plant heights as compared with the wild-type plants, suggesting that overexpression of OsBIRF1 promote plant growth. These results demonstrate that OsBIRF1 has pleiotropic effects on growth and defense response against multiple abiotic and biotic stresses.

Topics: Abscisic Acid; Amino Acid Sequence; Carboxylic Acids; Cyclopentanes; Gene Expression Regulation, Plant; Germination; Hydrogen Peroxide; Immunity, Innate; Magnaporthe; Molecular Sequence Data; Nicotiana; Oryza; Oxidative Stress; Oxylipins; Paraquat; Plant Diseases; Plant Proteins; Plant Roots; Plants, Genetically Modified; Pseudomonas syringae; Salicylic Acid; Seeds; Thiadiazoles; Tobacco Mosaic Virus

Induction of local defence, as well as systemic resistance, of plants is associated with transcriptional reprogramming. Here we report on defence gene induction by natural and synthetic stimulants of plant immunity. Gene expression changes in Arabidopsis thaliana were monitored in response to several plant immunity stimulants (plant activators) using Northern blotting and an application-based array representing c. 750 genes involved in several aspects of plant defence and/or plant stress. The commercial plant activators Bio-S, Neudo-Vital and PRORADIX have been shown to induce systemic resistance. Here, Neudo-Vital, PRORADIX and Bio-S treatment induced different patterns of salicylic acid (SA) and jasmonic acid (JA) accumulation. Gene induction by these plant activators proved to be very complex. Rather than simply mimicking one of the known defence pathways induced by SA or JA, the response to the plant activators showed aspects of both major defence systems. A general feature was the transient activation of JA biosynthesis genes, combined with a much more sustained SA-associated defence gene induction. Our results demonstrate that plant immunity stimulants activate systemic immunity at the transcriptional level, and they provide insight into the coordinated transcriptional regulation of several classes of plant defence genes.

Topics: Arabidopsis; Cluster Analysis; Cyclopentanes; Gene Expression Regulation, Plant; Microarray Analysis; Oxylipins; Plant Extracts; Salicylic Acid; Signal Transduction; Thiadiazoles; Transcriptional Activation

The non-protein amino acid beta-amino-butyric acid (BABA) protects plants against a wide range of pathogens. We have examined the effectiveness and mode of action of BABA on resistance against two necrotrophic pathogens. Treatment of Arabidopsis with BABA induced resistance against Alternaria brassicicola and Plectosphaerella cucumerina to a similar level by jasmonic acid (JA). Conversely, treatment with benzothiadiazole (BTH), a functional analogue of salicylic acid (SA), had no significant effect on the resistance against both pathogens. BABA-induced resistance against A. brassicicola and P. cucumerina was unaffected in the JA-insensitive mutant coi1-1 and the camalexin-deficient mutant pad3-1. Moreover, the expression of BABA-induced resistance was not associated with enhanced accumulation of camalexin or enhanced transcription of the JA-inducible PDF1.2 gene. The expression of BABA-induced resistance against P. cucumerina was unaffected in mutants impaired in ethylene (ET) and SA signalling, but was blocked in the abscisic acid (ABA)-deficient mutant aba1-5, the ABA-insensitive mutant abi4-1 and the callose-deficient mutant pmr4-1. Upon infection by both pathogens, BABA-treated plants showed an earlier and more pronounced accumulation of callose. Treatment with the callose-inhibitor 2-deoxy-D-glucose (2-DDG) reversed the BABA-induced resistance against A. brassicicola. Furthermore, primed callose deposition was absent in BABA-treated abi4-1 and pmr4-1 plants upon infection by P. cucumerina. Although the expression of BABA-induced resistance was not associated with enhanced transcription of the ABA-inducible RAB18 gene, application of ABA mimicked the effect of BABA on the level of callose accumulation and resistance. Hence, BABA-induced resistance against necrotrophic pathogens is based on primed callose accumulation, which is controlled by an ABA-dependent defence pathway.

Topics: Abscisic Acid; Alternaria; Aminobutyrates; Arabidopsis; Cyclopentanes; Genes, Plant; Glucans; Indoles; Mutation; Oxylipins; Phyllachorales; Plant Diseases; Plants, Genetically Modified; Salicylic Acid; Signal Transduction; Thiadiazoles; Thiazoles

We examined the effects of three forms of host plant resistance in tomato, Lycopersicon esculentum, on the potato aphid, Macrosiphum euphorbiae. Mi-1.2, a resistance gene (R-gene) in tomato that deters aphid feeding, reduced the population growth of both potato aphid isolates tested, although it appeared to have a greater impact on isolate WU11 than on isolate WU12. The results suggest that there may be quantitative differences in virulence between these two aphid isolates. We also examined two distinct forms of acquired resistance in tomato, jasmonic acid (JA)-dependent and salicylic acid (SA)-dependent induced defenses. Exogenous foliar application of JA triggered expression of a JA-inducible proteinase inhibitor in tomato cultivars with and without Mi-1.2, although the effects of treatment on aphid performance differed between these cultivars. JA-treatment reduced aphid population growth on a susceptible tomato cultivar that lacks Mi-1.2, but did not significantly enhance or inhibit aphid control on a near-isogenic resistant tomato cultivar that carries this gene. Foliar application of an SA analog, benzothiadiazole (BTH), was used to induce SA-dependent defenses. BTH treatment reduced the population growth of both aphid isolates on a susceptible tomato cultivar, and also enhanced aphid control on a resistant cultivar. The results indicate that both SA- and JA-dependent acquired resistance in tomato have a direct negative effect on a phloem-feeding insect. Furthermore, this study demonstrates that acquired resistance and R-gene-mediated resistance can interact for enhanced suppression of insect herbivores.

Topics: Animals; Aphids; Cyclopentanes; Genes, Plant; Host-Parasite Interactions; Oxylipins; Plant Diseases; Plant Leaves; Salicylic Acid; Solanum lycopersicum; Thiadiazoles

The activation of mitogen-activated protein kinases (MAPKs) has been previously implicated in signal transduction during plant responses to pathogen attack as well as to various environmental stresses. We have isolated from rice a new MAPK cDNA, OsBIMK1 ( O ryza s ativa L. BTH-induced MAPK 1), which encodes a 369-amino-acid protein with moderate to high nucleotide sequence similarity to previously reported plant MAPK genes. OsBIMK1 contains all 11 of the MAPK conserved subdomains and the phosphorylation-activation motif, TEY. We analyzed in detail the expression of OsBIMK1 upon treatment with various chemical and biological inducers of resistance responses in rice and in both incompatible and compatible interactions between rice and Magnaporthe grisea. Expression of OsBIMK1 was activated rapidly upon treatment with benzothiadiazole (BTH) as well as with dichloroisonicotinic acid, probenazole, jasmonic acid and its methyl ester, Pseudomonas syringae pv. syringae, or wounding. Expression of OsBIMK1 was induced rapidly during the first 36 h after inoculation with M. grisea in BTH-treated rice seedlings and in an incompatible interaction between M. grisea and a blast-resistant rice genotype. BTH treatment induced a systemic activation of OsBIMK1 expression. These results suggest that OsBIMK1 plays an important role in rice disease resistance.

Topics: Acetates; Amino Acid Sequence; Base Sequence; Cloning, Molecular; Cyclopentanes; DNA, Complementary; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Immunity, Innate; Isonicotinic Acids; Magnaporthe; Mitogen-Activated Protein Kinases; Molecular Sequence Data; Oryza; Oxylipins; Phylogeny; Plant Diseases; Pseudomonas; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Signal Transduction; Stress, Mechanical; Thiadiazoles; Thiazoles

Identification of host genes involved in defense responses is one of most critical steps leading to the elucidation of disease resistance mechanisms in plants. In this study, two different cloning strategies were employed to identify defense-related genes from a tropical japonica rice cultivar (Oryza sativa cv. Drew). With the use of bacterial colony arrays, differential screening of a blast fungus (Pyricularia grisea)-induced rice cDNA library led to the isolation of 22 distinct rice genes that are expressed differentially in response to blast infection. Sequence analysis indicates that most of them are full-length cDNAs encoding pathogenesis-related proteins or other relatively abundant proteins. In combination with treatments of cycloheximide plus jasmonic acid (JA) or benzothiadiazole (BTH) in rice seedlings, the polymerase chain reaction-based suppression subtractive hybridization also was conducted to search for immediate early (IE) defense-related genes whose transcription is independent of de novo protein synthesis. The initial screening of only 768 subtracted clones resulted in the identification of 34 distinct IE genes that are induced by JA, BTH, and/or blast infection. Database searches revealed that these IE genes encode putative mitogen-activated protein kinase, diacylglycerol kinase, zinc finger protein, RelA-SpoT protein, ankyrin-containing protein, ABC transporter, beta-ketoacyl-CoA synthase, and other potential defense-signaling components. Further characterization of these novel IE genes will likely facilitate the elucidation of defense signal transduction in rice plants.

Topics: Cycloheximide; Cyclopentanes; DNA, Plant; Gene Expression Regulation, Plant; Gene Library; Genes, Plant; Immunity, Innate; Magnaporthe; Nucleic Acid Hybridization; Oryza; Oxylipins; Plant Diseases; Polymerase Chain Reaction; Sequence Homology, Nucleic Acid; Thiadiazoles; Tropical Climate

Fungicide action is generally assumed to be dependent on an antibiotic effect on a target pathogen, although a role for plant defense mechanisms as mediators of fungicide action has not been excluded. Here, we demonstrate that in Arabidopsis, the innate plant defense mechanism contributes to the effectiveness of fungicides. In NahG and nim1 (for noninducible immunity) Arabidopsis plants, which normally exhibit increased susceptibility to pathogens, the fungicides metalaxyl, fosetyl, and Cu(OH)2 are much less active and fail to control Peronospora parasitica. In contrast, the effectiveness of these fungicides is not altered in Arabidopsis mutants defective in the ethylene or jasmonic acid signal transduction pathways. Application of the systemic acquired resistance activator benzothiadiazole (BTH) in combination with these fungicides results in a synergistic effect on pathogen resistance in wild-type plants and an additive effect in NahG and BTH-unresponsive nim1 plants. Interestingly, BTH treatment normally induces long-lasting pathogen protection; however, in NahG plants, the protection is transient. These observations suggest that BTH treatment can compensate only partially for an impaired signal transduction pathway and support the idea that pathogen defense mechanisms are under positive feedback control. These observations are strikingly reminiscent of the reduced efficacy of antifungal agents in immunocompromised animals.

Topics: Animals; Arabidopsis; Cyclopentanes; Drug Synergism; Ethylenes; Feedback; Fungicides, Industrial; Genes, Plant; Mutation; Oomycetes; Oxylipins; Plant Diseases; Signal Transduction; Thiadiazoles