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1.
BMC Plant Biol ; 21(1): 402, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34470613

RESUMO

BACKGROUND: Plant-parasitic nematodes and herbivorous insects have a significant negative impact on global crop production. A successful approach to protect crops from these pests is the in planta expression of nematotoxic or entomotoxic proteins such as crystal proteins from Bacillus thuringiensis (Bt) or plant lectins. However, the efficacy of this approach is threatened by emergence of resistance in nematode and insect populations to these proteins. To solve this problem, novel nematotoxic and entomotoxic proteins are needed. During the last two decades, several cytoplasmic lectins from mushrooms with nematicidal and insecticidal activity have been characterized. In this study, we tested the potential of Marasmius oreades agglutinin (MOA) to furnish Arabidopsis plants with resistance towards three economically important crop pests: the two plant-parasitic nematodes Heterodera schachtii and Meloidogyne incognita and the herbivorous diamondback moth Plutella xylostella. RESULTS: The expression of MOA does not affect plant growth under axenic conditions which is an essential parameter in the engineering of genetically modified crops. The transgenic Arabidopsis lines showed nearly complete resistance to H. schachtii, in that the number of female and male nematodes per cm root was reduced by 86-91 % and 43-93 % compared to WT, respectively. M. incognita proved to be less susceptible to the MOA protein in that 18-25 % and 26-35 % less galls and nematode egg masses, respectively, were observed in the transgenic lines. Larvae of the herbivorous P. xylostella foraging on MOA-expression lines showed a lower relative mass gain (22-38 %) and survival rate (15-24 %) than those feeding on WT plants. CONCLUSIONS: The results of our in planta experiments reveal a robust nematicidal and insecticidal activity of the fungal lectin MOA against important agricultural pests which may be exploited for crop protection.


Assuntos
Aglutininas/farmacologia , Arabidopsis/parasitologia , Herbivoria , Marasmius/química , Nematoides/fisiologia , Aglutininas/química , Animais , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Mariposas/fisiologia , Doenças das Plantas/prevenção & controle , Plantas Geneticamente Modificadas
2.
Plants (Basel) ; 10(9)2021 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-34579478

RESUMO

Plants are frequently exposed to simultaneous abiotic and biotic stresses, a condition that induces complex responses, negatively affects crop productivity and is becoming more exacerbated with current climate change. In this study, we investigated the effects of individual and combined heat and osmotic stresses on Arabidopsis susceptibility to the biotrophic pathogen Pseudomonas syringae pv. tomato (Pst) and the necrotrophic pathogen Botrytiscinerea (Bc). Our data showed that combined abiotic and biotic stresses caused an enhanced negative impact on plant disease resistance in comparison with individual Pst and Bc infections. Pretreating plants with individual heat or combined osmotic-heat stress strongly reduced the expression of many defense genes including pathogenesis-related proteins (PR-1 and PR-5) and the TN-13 gene encoding the TIR-NBS protein, which are involved in disease resistance towards Pst. We also found that combined osmotic-heat stress caused high plant susceptibility to Bc infection and reduced expression of a number of defense genes, including PLANT DEFENSIN 1.3 (PDF1.3), BOTRYTIS SUSCEPTIBLE 1 (BOS1) and THIONIN 2.2 (THI2.2) genes, which are important for disease resistance towards Bc. The impaired disease resistance against both Pst and Bc under combined abiotic stress is associated with reduced expression of cell wall-related genes. Taken together, our data emphasize that the combination of global warming-associated abiotic stresses such as heat and osmotic stresses makes plants more susceptible to pathogen infection, thus threatening future global food security.

3.
Front Plant Sci ; 12: 657451, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33897746

RESUMO

Coprinopsis cinerea lectin 2 (CCL2) is a fucoside-binding lectin from the basidiomycete C. cinerea that is toxic to the bacterivorous nematode Caenorhabditis elegans as well as animal-parasitic and fungivorous nematodes. We expressed CCL2 in Arabidopsis to assess its protective potential toward plant-parasitic nematodes. Our results demonstrate that expression of CCL2 enhances host resistance against the cyst nematode Heterodera schachtii. Surprisingly, CCL2-expressing plants were also more resistant to fungal pathogens including Botrytis cinerea, and the phytopathogenic bacterium Pseudomonas syringae. In addition, CCL2 expression positively affected plant growth indicating that CCL2 has the potential to improve two important agricultural parameters namely biomass production and general disease resistance. The mechanism of the CCL2-mediated enhancement of plant disease resistance depended on fucoside-binding by CCL2 as transgenic plants expressing a mutant version of CCL2 (Y92A), compromised in fucoside-binding, exhibited wild type (WT) disease susceptibility. The protective effect of CCL2 did not seem to be direct as the lectin showed no growth-inhibition toward B. cinerea in in vitro assays. We detected, however, a significantly enhanced transcriptional induction of plant defense genes in CCL2- but not CCL2-Y92A-expressing lines in response to infection with B. cinerea compared to WT plants. This study demonstrates a potential of fungal defense lectins in plant protection beyond their use as toxins.

4.
Nat Nanotechnol ; 16(3): 344-353, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33318639

RESUMO

In plants, pathogen attack can induce an immune response known as systemic acquired resistance that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO2 NPs; food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO2 NP-induced disease resistance are unknown. Here we show that SiO2 NPs, as well as soluble Si(OH)4, can induce systemic acquired resistance in a dose-dependent manner, which involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through the stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in the air spaces in the spongy mesophyll of the leaf. In contrast to the treatment with SiO2 NPs, the induction of systemic acquired resistance by Si(OH)4 was problematic since high Si(OH)4 concentrations caused stress. We conclude that SiO2 NPs have the potential to serve as an inexpensive, highly efficient, safe and sustainable alternative for plant disease protection.


Assuntos
Arabidopsis/efeitos dos fármacos , Resistência à Doença/genética , Nanopartículas/química , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Doenças das Plantas/genética , Doenças das Plantas/prevenção & controle , Espécies Reativas de Oxigênio/química , Ácido Salicílico/química , Dióxido de Silício/química , Dióxido de Silício/farmacologia
5.
New Phytol ; 227(5): 1467-1478, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32396661

RESUMO

Pathogen effectors act as disease promoting factors that target specific host proteins with roles in plant immunity. Here, we investigated the function of the RxLR3 effector of the plant-pathogen Phytophthora brassicae. Arabidopsis plants expressing a FLAG-RxLR3 fusion protein were used for co-immunoprecipitation followed by liquid chromatography-tandem mass spectrometry to identify host targets of RxLR3. Fluorescently labelled fusion proteins were used for analysis of subcellular localisation and function of RxLR3. Three closely related members of the callose synthase family, CalS1, CalS2 and CalS3, were identified as targets of RxLR3. RxLR3 co-localised with the plasmodesmal marker protein PDLP5 (PLASMODESMATA-LOCALISED PROTEIN 5) and with plasmodesmata-associated deposits of the ß-1,3-glucan polymer callose. In line with a function as an inhibitor of plasmodesmal callose synthases (CalS) enzymes, callose depositions were reduced and cell-to-cell trafficking was promoted in the presence of RxLR3. Plasmodesmal callose deposition in response to infection was compared with wild-type suppressed in RxLR3-expressing Arabidopsis lines. Our results implied a virulence function of the RxLR3 effector as a positive regulator of plasmodesmata transport and provided evidence for competition between P. brassicae and Arabidopsis for control of cell-to-cell trafficking.


Assuntos
Phytophthora , Plasmodesmos , Glucanos , Glucosiltransferases/genética
6.
Front Neurorobot ; 13: 77, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31619981

RESUMO

The human motor system is robust, adaptive and very flexible. The underlying principles of human motion provide inspiration for robotics. Pointing at different targets is a common robotics task, where insights about human motion can be applied. Traditionally in robotics, when a motion is generated it has to be validated so that the robot configurations involved are appropriate. The human brain, in contrast, uses the motor cortex to generate new motions reusing and combining existing knowledge before executing the motion. We propose a method to generate and control pointing motions for a robot using a biological inspired architecture implemented with spiking neural networks. We outline a simplified model of the human motor cortex that generates motions using motor primitives. The network learns a base motor primitive for pointing at a target in the center, and four correction primitives to point at targets up, down, left and right from the base primitive, respectively. The primitives are combined to reach different targets. We evaluate the performance of the network with a humanoid robot pointing at different targets marked on a plane. The network was able to combine one, two or three motor primitives at the same time to control the robot in real-time to reach a specific target. We work on extending this work from pointing to a given target to performing a grasping or tool manipulation task. This has many applications for engineering and industry involving real robots.

7.
Plant J ; 95(2): 187-203, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-29671919

RESUMO

Plant pathogens of the oomycete genus Phytophthora produce virulence factors, known as RxLR effector proteins that are transferred into host cells to suppress disease resistance. Here, we analyse the function of the highly conserved RxLR24 effector of Phytophthora brassicae. RxLR24 was expressed early in the interaction with Arabidopsis plants and ectopic expression in the host enhanced leaf colonization and zoosporangia formation. Co-immunoprecipitation (Co-IP) experiments followed by mass spectrometry identified different members of the RABA GTPase family as putative RxLR24 targets. Physical interaction of RxLR24 or its homologue from the potato pathogen Phytophthora infestans with different RABA GTPases of Arabidopsis or potato, respectively, was confirmed by reciprocal Co-IP. In line with the function of RABA GTPases in vesicular secretion, RxLR24 co-localized with RABA1a to vesicles and the plasma membrane. The effect of RxLR24 on the secretory process was analysed with fusion constructs of secreted antimicrobial proteins with a pH-sensitive GFP tag. PATHOGENESIS RELATED PROTEIN 1 (PR-1) and DEFENSIN (PDF1.2) were efficiently exported in control tissue, whereas in the presence of RxLR24 they both accumulated in the endoplasmic reticulum. Together our results imply a virulence function of RxLR24 effectors as inhibitors of RABA GTPase-mediated vesicular secretion of antimicrobial PR-1, PDF1.2 and possibly other defence-related compounds.


Assuntos
Peptídeos Catiônicos Antimicrobianos/metabolismo , Arabidopsis/microbiologia , Vesículas Extracelulares/metabolismo , Proteínas Fúngicas/fisiologia , Phytophthora/fisiologia , Doenças das Plantas/microbiologia , Solanum tuberosum/microbiologia , Fatores de Virulência/fisiologia , Proteínas rab de Ligação ao GTP/metabolismo , Arabidopsis/imunologia , Arabidopsis/fisiologia , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Interações Hospedeiro-Patógeno , Imunoprecipitação , Phytophthora/genética , Phytophthora/metabolismo , Doenças das Plantas/imunologia , Folhas de Planta/microbiologia , Solanum tuberosum/imunologia , Solanum tuberosum/fisiologia , Fatores de Virulência/genética , Fatores de Virulência/metabolismo
8.
J Exp Bot ; 68(5): 1169-1183, 2017 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-28062592

RESUMO

Mitogen-activated protein kinases (MAPKs) mediate plant immune responses to pathogenic bacteria. However, less is known about the cell autonomous negative regulatory mechanism controlling basal plant immunity. We report the biological role of Arabidopsis thaliana MAPK phosphatase AP2C1 as a negative regulator of plant basal resistance and defense responses to Pseudomonas syringae. AP2C2, a closely related MAPK phosphatase, also negatively controls plant resistance. Loss of AP2C1 leads to enhanced pathogen-induced MAPK activities, increased callose deposition in response to pathogen-associated molecular patterns or to P. syringae pv. tomato (Pto) DC3000, and enhanced resistance to bacterial infection with Pto. We also reveal the impact of AP2C1 on the global transcriptional reprogramming of transcription factors during Pto infection. Importantly, ap2c1 plants show salicylic acid-independent transcriptional reprogramming of several defense genes and enhanced ethylene production in response to Pto. This study pinpoints the specificity of MAPK regulation by the different MAPK phosphatases AP2C1 and MKP1, which control the same MAPK substrates, nevertheless leading to different downstream events. We suggest that precise and specific control of defined MAPKs by MAPK phosphatases during plant challenge with pathogenic bacteria can strongly influence plant resistance.


Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Fosfoproteínas Fosfatases/genética , Imunidade Vegetal , Proteínas Tirosina Fosfatases/genética , Pseudomonas syringae/fisiologia , Arabidopsis/imunologia , Arabidopsis/microbiologia , Proteínas de Arabidopsis/metabolismo , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Fosfoproteínas Fosfatases/metabolismo , Proteínas Tirosina Fosfatases/metabolismo
9.
Plant J ; 89(3): 502-509, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-27747953

RESUMO

Pathogenesis-related proteins played a pioneering role 50 years ago in the discovery of plant innate immunity as a set of proteins that accumulated upon pathogen challenge. The most abundant of these proteins, PATHOGENESIS-RELATED 1 (PR-1) encodes a small antimicrobial protein that has become, as a marker of plant immune signaling, one of the most referred to plant proteins. The biochemical activity and mode of action of PR-1 proteins has remained elusive, however. Here, we provide genetic and biochemical evidence for the capacity of PR-1 proteins to bind sterols, and demonstrate that the inhibitory effect on pathogen growth is caused by the sequestration of sterol from pathogens. In support of our findings, sterol-auxotroph pathogens such as the oomycete Phytophthora are particularly sensitive to PR-1, whereas sterol-prototroph fungal pathogens become highly sensitive only when sterol biosynthesis is compromised. Our results are in line with previous findings showing that plants with enhanced PR-1 expression are particularly well protected against oomycete pathogens.


Assuntos
Proteínas de Plantas/metabolismo , Plantas/metabolismo , Esteróis/metabolismo , Anti-Infecciosos/metabolismo , Colesterol/metabolismo , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Interações Hospedeiro-Patógeno , Immunoblotting , Lycopersicon esculentum/genética , Lycopersicon esculentum/metabolismo , Lycopersicon esculentum/microbiologia , Phytophthora/fisiologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Proteínas de Plantas/genética , Plantas/genética , Plantas/microbiologia , Ligação Proteica , Tabaco/genética , Tabaco/metabolismo , Tabaco/microbiologia
10.
Mol Plant ; 9(5): 662-681, 2016 05 02.
Artigo em Inglês | MEDLINE | ID: mdl-26802249

RESUMO

Tryptophan-derived, indolic metabolites possess diverse functions in Arabidopsis innate immunity to microbial pathogen infection. Here, we investigate the functional role and regulatory characteristics of indolic metabolism in Arabidopsis systemic acquired resistance (SAR) triggered by the bacterial pathogen Pseudomonas syringae. Indolic metabolism is broadly activated in both P. syringae-inoculated and distant, non-inoculated leaves. At inoculation sites, camalexin, indol-3-ylmethylamine (I3A), and indole-3-carboxylic acid (ICA) are the major accumulating compounds. Camalexin accumulation is positively affected by MYB122, and the cytochrome P450 genes CYP81F1 and CYP81F2. Local I3A production, by contrast, occurs via indole glucosinolate breakdown by PEN2- dependent and independent pathways. Moreover, exogenous application of the defense hormone salicylic acid stimulates I3A generation at the expense of its precursor indol-3-ylmethylglucosinolate (I3M), and the SAR regulator pipecolic acid primes plants for enhanced P. syringae-induced activation of distinct branches of indolic metabolism. In uninfected systemic tissue, the metabolic response is more specific and associated with enhanced levels of the indolics I3A, ICA, and indole-3-carbaldehyde (ICC). Systemic indole accumulation fully depends on functional CYP79B2/3, PEN2, and MYB34/51/122, and requires functional SAR signaling. Genetic analyses suggest that systemically elevated indoles are dispensable for SAR and associated systemic increases of salicylic acid. However, soil-grown but not hydroponically -cultivated cyp79b2/3 and pen2 plants, both defective in indolic secondary metabolism, exhibit pre-induced immunity, which abrogates their intrinsic ability to induce SAR.


Assuntos
Doenças das Plantas/microbiologia , Arabidopsis/metabolismo , Arabidopsis/microbiologia , Resistência à Doença/genética , Resistência à Doença/fisiologia , Regulação da Expressão Gênica de Plantas/genética , Regulação da Expressão Gênica de Plantas/fisiologia , Imunidade Inata/genética , Imunidade Inata/fisiologia , Indóis/metabolismo , Doenças das Plantas/genética , Pseudomonas syringae/patogenicidade , Tiazóis/metabolismo
11.
J Exp Bot ; 64(11): 3385-95, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23833195

RESUMO

Pathogen and Circadian Controlled 1 (PCC1) was previously characterized as a regulator of defence against pathogens and stress-activated transition to flowering. Plants expressing an RNA interference construct for the PCC1 gene (iPCC1 plants) showed a pleiotropic phenotype. They were hypersensitive to abscisic acid (ABA) as shown by reduced germination potential and seedling establishment, as well as reduced stomatal aperture and main root length in ABA-supplemented media. In addition, iPCC1 plants displayed alterations in polar lipid contents and their corresponding fatty acids. Importantly, a significant reduction in the content of phosphatidylinositol (PI) was observed in iPCC1 leaves when compared with wild-type plants. A trend in reduced levels of 18:0 and increased levels of 18:2 and particularly 18:3 was also detected in several classes of polar lipids. The enhanced ABA-mediated responses and the reduced content of PI might be responsible for iPCC1 plants displaying a complex pattern of defence against pathogens of different lifestyles. iPCC1 plants were more susceptible to the hemi-biotrophic oomycete pathogen Phytophthora brassicae and more resistant to the necrotrophic fungal pathogen Botrytis cinerea compared with wild-type plants.


Assuntos
Ácido Abscísico/farmacologia , Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Arabidopsis/efeitos dos fármacos , Proteínas de Arabidopsis/genética , Resistência à Doença/efeitos dos fármacos , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Fosfatidilinositóis/metabolismo , Doenças das Plantas
12.
Plant Physiol ; 162(4): 1815-21, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23757404

RESUMO

Salicylic acid (SA) is central for the defense of plants to pathogens and abiotic stress. SA is synthesized in chloroplasts from chorismic acid by an isochorismate synthase (ICS1); SA biosynthesis is negatively regulated by autoinhibitory feedback at ICS1. Genetic studies indicated that the multidrug and toxin extrusion transporter ENHANCED DISEASE SUSCEPTIBILITY5 (EDS5) of Arabidopsis (Arabidopsis thaliana) is necessary for SA accumulation after biotic and abiotic stress, but so far it is not understood how EDS5 controls the biosynthesis of SA. Here, we show that EDS5 colocalizes with a marker of the chloroplast envelope and that EDS5 functions as a multidrug and toxin extrusion-like transporter in the export of SA from the chloroplast to the cytoplasm in Arabidopsis, where it controls the innate immune response. The location at the chloroplast envelope supports a model of the effect of EDS5 on SA biosynthesis: in the eds5 mutant, stress-induced SA is trapped in the chloroplast and inhibits its own accumulation by autoinhibitory feedback.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Cloroplastos/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Ácido Salicílico/metabolismo , Arabidopsis/efeitos dos fármacos , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Transporte Biológico , Carbonil Cianeto m-Clorofenil Hidrazona/farmacologia , Cloroplastos/genética , Citoplasma/genética , Citoplasma/metabolismo , Imunidade Inata , Proteínas de Membrana Transportadoras/genética , Dados de Sequência Molecular , Mutação , Nigericina/farmacologia , Plantas Geneticamente Modificadas , Protoplastos/metabolismo , Raios Ultravioleta
13.
Plant Physiol ; 157(4): 2000-12, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-22007023

RESUMO

The Arabidopsis (Arabidopsis thaliana) phytoalexin-deficient mutant pad2-1 displays enhanced susceptibility to a broad range of pathogens and herbivorous insects that correlates with deficiencies in the production of camalexin, indole glucosinolates, and salicylic acid (SA). The pad2-1 mutation is localized in the GLUTAMATE-CYSTEINE LIGASE (GCL) gene encoding the first enzyme of glutathione biosynthesis. While pad2-1 glutathione deficiency is not caused by a decrease in GCL transcripts, analysis of GCL protein level revealed that pad2-1 plants contained only 48% of the wild-type protein amount. In contrast to the wild type, the oxidized form of GCL was dominant in pad2-1, suggesting a distinct redox environment. This finding was corroborated by the expression of GRX1-roGFP2, showing that the cytosolic glutathione redox potential was significantly less negative in pad2-1. Analysis of oxidative stress-related gene expression showed a higher transcript accumulation in pad2-1 of GLUTATHIONE REDUCTASE, GLUTATHIONE-S-TRANSFERASE, and RESPIRATORY BURST OXIDASE HOMOLOG D in response to the oomycete Phytophthora brassicae. Interestingly, oligogalacturonide elicitation in pad2-1 revealed a lower plasma membrane depolarization that was found to act upstream of an impaired hydrogen peroxide production. This impaired hydrogen peroxide production was also observed during pathogen infection and correlated with a reduced hypersensitive response in pad2-1. In addition, a lack of pathogen-triggered expression of the ISOCHORISMATE SYNTHASE1 gene, coding for the SA-biosynthetic enzyme isochorismate synthase, was identified as the cause of the SA deficiency in pad2-1. Together, our results indicate that the pad2-1 mutation is related to a decrease in GCL protein and that the resulting glutathione deficiency negatively affects important processes of disease resistance.


Assuntos
Arabidopsis/fisiologia , Regulação da Expressão Gênica de Plantas/fisiologia , Glutamato-Cisteína Ligase/metabolismo , Glutationa/metabolismo , Oligossacarídeos/farmacologia , Phytophthora/fisiologia , Anti-Infecciosos/metabolismo , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Arabidopsis/parasitologia , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Membrana Celular/metabolismo , Suscetibilidade a Doenças , Glutamato-Cisteína Ligase/genética , Interações Hospedeiro-Patógeno , Peróxido de Hidrogênio/metabolismo , Mutação , Óxido Nítrico/metabolismo , Oxirredução , Estresse Oxidativo , Doenças das Plantas/parasitologia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/genética , Folhas de Planta/parasitologia , Folhas de Planta/fisiologia , Espécies Reativas de Oxigênio/metabolismo , Ácido Salicílico/metabolismo , Transdução de Sinais , Estresse Fisiológico
14.
Plant J ; 62(5): 840-51, 2010 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-20230487

RESUMO

We have analysed the role of tryptophan-derived secondary metabolites in disease resistance of Arabidopsis to the oomycete pathogen Phytophthora brassicae. Transcript analysis revealed that genes encoding enzymes involved in tryptophan, camalexin and indole glucosinolate (iGS) biosynthesis are coordinately induced in response to P. brassicae. However, a deficiency in either camalexin or iGS accumulation has only a minor effect on the disease resistance of Arabidopsis mutants. In contrast, the double mutant cyp79B2 cyp79B3, which has a blockage in the production of indole-3-aldoxime (IAOx), the common precursor of tryptophan-derived metabolites including camalexin and iGS, is highly susceptible to P. brassicae. Because cyp79B2 cyp79B3 shows no deficiencies in other tested disease resistance responses, we concluded that the lack of IAOx-derived compounds renders Arabidopsis susceptible despite wild-type-like pathogen-induced hypersensitive cell death, stress hormone signaling and callose deposition. The susceptibility of the double mutant pen2-1 pad3-1, which has a combined defect in camalexin synthesis and PEN2-catalysed hydrolysis of iGS compounds, demonstrates that both camalexin and products of iGS hydrolysis are important for disease resistance to P. brassicae. Products of iGS hydrolysis play an early defensive role, as indicated by enhanced epidermal penetration rates of Arabidopsis mutants affected in iGS synthesis or degradation. Our results show that disease resistance of Arabidopsis to P. brassicae is established by the sequential activity of the phytoanticipin iGS and the phytoalexin camalexin.


Assuntos
Arabidopsis/metabolismo , Glucosinolatos/metabolismo , Indóis/metabolismo , Phytophthora/fisiologia , Doenças das Plantas/genética , Tiazóis/metabolismo , Arabidopsis/genética , Arabidopsis/imunologia , Regulação da Expressão Gênica de Plantas , Imunidade Inata , Mutação , Doenças das Plantas/imunologia , RNA de Plantas/genética
15.
Plant Signal Behav ; 5(9): 1099-101, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-21490418

RESUMO

The model plant Arabidopsis thaliana contains a large arsenal of secondary metabolites that are not essential in development but have important ecological functions in counteracting attacks of pathogens and herbivores. Preformed secondary compounds are often referred to as phytoanticipins and metabolites, that are synthesized de novo in response to biotic stress are known as phytoalexins. Camalexin is the typical phytoalexin of Arabidopsis. It has antimicrobial activity towards some pathogens and was shown to be an important component of disease resistance in several plant pathogen interactions. Glucosinolates (GS) are characteristic phytoanticipins of the Brassicaceae family including Arabidopsis. GS are best known as repellents or attractants for herbivorous insects and their predators whereas their antimicrobial potential has received relatively little attention. The GS are glucosides and the biologically active aglycone is released upon biotic stress by glucohydrolase enzymes commenly called myrosinases. Because an Arabidopsis mutant susceptible to the oomycete pathogen Phytophthora brassicae shows a partial deficiency in both camalexin and iGS accumulation we became intrigued by the role of these secondary compounds in disease resistance. Our results show that disease resistance of Arabidopsis to P. brassicae is established by the combined action of iGS and camalexin.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Resistência à Doença/fisiologia , Glucosinolatos/metabolismo , Indóis/metabolismo , Phytophthora , Doenças das Plantas/microbiologia , Tiazóis/metabolismo , Mutação , Sesquiterpenos/metabolismo
16.
Plant J ; 58(2): 287-98, 2009 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19170932

RESUMO

Plant immune responses to pathogens are often associated with enhanced production of reactive oxygen species (ROS), known as the oxidative burst, and with rapid hypersensitive host cell death (the hypersensitive response, HR) at sites of attempted infection. It is generally accepted that the oxidative burst acts as a promotive signal for HR, and that HR is highly correlated with efficient disease resistance. We have identified the Arabidopsis mutant rph1 (resistance to Phytophthora 1), which is susceptible to the oomycete pathogen Phytophthora brassicae despite rapid induction of HR. The susceptibility of rph1 was specific for P. brassicae and coincided with a reduced oxidative burst, a runaway cell-death response, and failure to properly activate the expression of defence-related genes. From these results, we conclude that, in the immune response to P. brassicae, (i) HR is not sufficient to stop the pathogen, (ii) HR initiation can occur in the absence of a major oxidative burst, (iii) the oxidative burst plays a role in limiting the spread of cell death, and (iv) RPH1 is a positive regulator of the P. brassicae-induced oxidative burst and enhanced expression of defence-related genes. Surprisingly, RPH1 encodes an evolutionary highly conserved chloroplast protein, indicating a function of this organelle in activation of a subset of immune reactions in response to P. brassicae. The disease resistance-related role of RPH1 was not limited to the Arabidopsis model system. Silencing of the potato homolog StRPH1 in a resistant potato cultivar caused susceptibility to the late blight pathogen Phytophthora infestans.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Cloroplastos/metabolismo , Phytophthora/crescimento & desenvolvimento , Sequência de Aminoácidos , Arabidopsis/genética , Arabidopsis/imunologia , Proteínas de Arabidopsis/genética , Morte Celular , Cloroplastos/genética , DNA de Plantas/genética , Regulação da Expressão Gênica de Plantas , Inativação Gênica , Teste de Complementação Genética , Peróxido de Hidrogênio , Dados de Sequência Molecular , Mutagênese Insercional , Estresse Oxidativo , Doenças das Plantas/genética , Doenças das Plantas/imunologia , Alinhamento de Sequência , Análise de Sequência de DNA , Solanum tuberosum/genética , Solanum tuberosum/metabolismo
17.
Plant J ; 55(5): 774-86, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18466300

RESUMO

Summary Plants often respond to pathogen or insect attack by inducing the synthesis of toxic compounds such as phytoalexins and glucosinolates (GS). The Arabidopsis mutant pad2-1 has reduced levels of the phytoalexin camalexin and is known for its increased susceptibility to fungal and bacterial pathogens. We found that pad2-1 is also more susceptible to the generalist insect Spodoptera littoralis but not to the specialist Pieris brassicae. The PAD2 gene encodes a gamma-glutamylcysteine synthetase that is involved in glutathione (GSH) synthesis, and consequently the pad2-1 mutant contains about 20% of the GSH found in wild-type plants. Lower GSH levels of pad2-1 were correlated with reduced accumulation of the two major indole and aliphatic GSs of Arabidopsis, indolyl-3-methyl-GS and 4-methylsulfinylbutyl-GS, in response to insect feeding. This effect was specific to GSH, was not complemented by treatment of pad2-1 with the strong reducing agent dithiothreitol, and was not observed with the ascorbate-deficient mutant vtc1-1. In contrast to the jasmonate-insensitive mutant coi1-1, expression of insect-regulated and GS biosynthesis genes was not affected in pad2-1. Our data suggest a crucial role for GSH in GS biosynthesis and insect resistance.


Assuntos
Arabidopsis/metabolismo , Glucosinolatos/biossíntese , Glutamato-Cisteína Ligase/metabolismo , Glutationa/metabolismo , Spodoptera/fisiologia , Animais , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , DNA de Plantas/genética , Regulação da Expressão Gênica de Plantas , Genótipo , Glutamato-Cisteína Ligase/genética , Análise de Sequência com Séries de Oligonucleotídeos
18.
Gene ; 408(1-2): 1-8, 2008 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-18024004

RESUMO

Lateral gene transfer (LGT) can facilitate the acquisition of new functions in recipient lineages, which may enable them to colonize new environments. Several recent publications have shown that gene transfer between prokaryotes and eukaryotes occurs with appreciable frequency. Here we present a study of interdomain gene transfer of cutinases -- well documented virulence factors in fungi -- between eukaryotic plant pathogens Phytophthora species and prokaryotic bacterial lineages. Two putative cutinase genes were cloned from Phytophthora brassicae and Northern blotting experiments showed that these genes are expressed early during the infection of the host Arabidopsis thaliana and induced during cyst germination of the pathogen. Analysis of the gene organisation of this gene family in Phytophthora ramorum and P. sojae showed three and ten copies in tight succession within a region of 5 and 25 kb, respectively, probably indicating a recent expansion in Phytophthora lineages by gene duplications. Bioinformatic analyses identified orthologues only in three genera of Actinobacteria, and in two distantly related eukaryotic groups: oomycetes and fungi. Together with phylogenetic analyses this limited distribution of the gene in the tree of life strongly support a scenario where cutinase genes originated after the origin of land plants in a microbial lineage living in proximity of plants and subsequently were transferred between distantly related plant-degrading microbes. More precisely, a cutinase gene was likely acquired by an ancestor of P. brassicae, P. sojae, P. infestans and P. ramorum, possibly from an actinobacterial source, suggesting that gene transfer might be an important mechanism in the evolution of their virulence. These findings could indeed provide an interesting model system to study acquisition of virulence factors in these important plant pathogens.


Assuntos
Hidrolases de Éster Carboxílico/genética , Evolução Molecular , Transferência Genética Horizontal , Phytophthora/genética , Fatores de Virulência/genética , Proteínas de Algas/genética , DNA de Algas/metabolismo , Família Multigênica , Filogenia , Phytophthora/patogenicidade
19.
Plant Cell ; 19(7): 2213-24, 2007 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-17630279

RESUMO

Wound signaling pathways in plants are mediated by mitogen-activated protein kinases (MAPKs) and stress hormones, such as ethylene and jasmonates. In Arabidopsis thaliana, the transmission of wound signals by MAPKs has been the subject of detailed investigations; however, the involvement of specific phosphatases in wound signaling is not known. Here, we show that AP2C1, an Arabidopsis Ser/Thr phosphatase of type 2C, is a novel stress signal regulator that inactivates the stress-responsive MAPKs MPK4 and MPK6. Mutant ap2c1 plants produce significantly higher amounts of jasmonate upon wounding and are more resistant to phytophagous mites (Tetranychus urticae). Plants with increased AP2C1 levels display lower wound activation of MAPKs, reduced ethylene production, and compromised innate immunity against the necrotrophic pathogen Botrytis cinerea. Our results demonstrate a key role for the AP2C1 phosphatase in regulating stress hormone levels, defense responses, and MAPK activities in Arabidopsis and provide evidence that the activity of AP2C1 might control the plant's response to B. cinerea.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Ciclopentanos/metabolismo , Etilenos/metabolismo , Proteínas Quinases Ativadas por Mitógeno/genética , Oxilipinas/metabolismo , Fosfoproteínas Fosfatases/metabolismo , Doenças das Plantas/imunologia , Arabidopsis/imunologia , Arabidopsis/microbiologia , Proteínas de Arabidopsis/genética , Biomarcadores , Botrytis , Regulação para Baixo/genética , Ativação Enzimática , Imunidade Inata , Doenças das Plantas/microbiologia , Ligação Proteica , Protoplastos/enzimologia , Saccharomyces cerevisiae/metabolismo
20.
Plant J ; 49(1): 159-72, 2007 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-17144898

RESUMO

The Arabidopsis pad2-1 mutant belongs to a series of non-allelic camalexin-deficient mutants. It was originally described as showing enhanced susceptibility to virulent strains of Pseudomonas syringae and was later shown to be hyper-susceptible to the oomycete pathogen Phytophthora brassicae (formerly P. porri). Surprisingly, in both pathosystems, the disease susceptibility of pad2-1 was not caused by the camalexin deficiency, suggesting additional roles of PAD2 in disease resistance. The susceptibility of pad2-1 to P. brassicae was used to map the mutation to the gene At4g23100, which encodes gamma-glutamylcysteine synthetase (gamma-ECS, GSH1). GSH1 catalyzes the first committed step of glutathione (GSH) biosynthesis. The pad2-1 mutation caused an S to N transition at amino acid position 298 close to the active center. The conclusion that PAD2 encodes GSH1 is supported by several lines of evidence: (i) pad2-1 mutants contained only about 22% of wild-type amounts of GSH, (ii) genetic complementation of pad2-1 with wild-type GSH1 cDNA restored GSH production, accumulation of camalexin in response to P. syringae and resistance to P. brassicae and P. syringae, (iii) another GSH1 mutant, cad2-1, showed pad2-like phenotypes, and (iv) feeding of GSH to excised leaves of pad2-1 restored camalexin production and resistance to P. brassicae. Inoculation of Col-0 with P. brassicae caused a coordinated increase in the transcript abundance of GSH1 and GSH2, the gene encoding the second enzyme in GSH biosynthesis, and resulted in enhanced foliar GSH accumulation. The pad2-1 mutant showed enhanced susceptibility to additional pathogens, suggesting an important general role of GSH in disease resistance of Arabidopsis.


Assuntos
Arabidopsis/metabolismo , Arabidopsis/microbiologia , Glutamato-Cisteína Ligase/metabolismo , Glutationa/metabolismo , Doenças das Plantas/microbiologia , Sequência de Aminoácidos , Arabidopsis/genética , Glutamato-Cisteína Ligase/genética , Dados de Sequência Molecular , Phytophthora/fisiologia , Pseudomonas syringae/fisiologia
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