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Salicylic Acid Signaling in Disease ResistanceKumar, Dhirendra 01 November 2014 (has links)
Salicylic acid (SA) is a key plant hormone that mediates host responses against microbial pathogens. Identification and characterization of SA-interacting/binding proteins is a topic which has always excited scientists studying microbial defense response in plants. It is likely that discovery of a true receptor for SA may greatly advance understanding of this important signaling pathway. SABP2 with its high affinity for SA was previously considered to be a SA receptor. Despite a great deal work we may still not have true a receptor for SA. It is also entirely possible that there may be more than one receptor for SA. This scenario is more likely given the diverse role of SA in various physiological processes in plants including, modulation of opening and closing of stomatal aperture, flowering, seedling germination, thermotolerance, photosynthesis, and drought tolerance. Recent identification of NPR3, NPR4 and NPR1 as potential SA receptors and α-ketoglutarate dehydrogenase (KGDHE2), several glutathione S transferases (GSTF) such as SA binding proteins have generated more interest in this field. Some of these SA binding proteins may have direct/indirect role in plant processes other than pathogen defense signaling. Development and use of new techniques with higher specificity to identify SA-interacting proteins have shown great promise and have resulted in the identification of several new SA interactors. This review focuses on SA interaction/binding proteins identified so far and their likely role in mediating plant defenses.
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Identification of Likely Orthologs of Tobacco Salicylic Acid-Binding Protein 2 and Their Role in Systemic Acquired Resistance in Arabidopsis ThalianaVlot, Anna, Liu, Po Pu, Cameron, Robin K., Park, Sang Wook, Yang, Yue, Kumar, Dhirendra, Zhou, Fasong, Padukkavidana, Thihan, Gustafsson, Claes, Pichersky, Eran, Klessig, Daniel F. 01 November 2008 (has links)
Salicylic acid-binding protein 2 (SABP2) is essential for the establishment of systemic acquired resistance (SAR) in tobacco; SABP2's methyl salicylate (MeSA) esterase activity is required in healthy systemic tissues of infected plants to release the active defense phytohormone SA from MeSA, which serves as a long-distance signal for SAR. In the current study, we characterize a new gene family from Arabidopsis thaliana encoding 18 potentially active α/β fold hydrolases that share 32-57% identity with SABP2. Of 14 recombinant AtMES (MES for methyl esterase) proteins tested, five showed preference for MeSA as a substrate and displayed SA inhibition of MeSA esterase activity in vitro (AtMES1, -2, -4, -7, and -9). The two genes encoding MeSA esterases with the greatest activity, AtMES1 and -9, as well as AtMES7 were transcriptionally upregulated during infection of Arabidopsis with avirulent Pseudomonas syringae. In addition, conditional expression of AtMES1, -7, or -9 complemented SAR deficiency in SABP2-silenced tobacco, suggesting that these three members of the AtMES family are SABP2 functional homologs (orthologs). Underexpression by knockout mutation and/or RNAi-mediated silencing of multiple AtMES genes, including AtMES1, -2, -7, and -9, compromised SAR in Arabidopsis and correlated with enhanced accumulation of MeSA in the systemic tissue of SAR-induced plants. Together, the data show that several members of the AtMES gene family are functionally homologous to SABP2 and redundant for MeSA hydrolysis and probably SAR. These data suggest that MeSA is a conserved SAR signal in Arabidopsis and tobacco.
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Fonction et régulation des histone-désacétylases en réponse au stress chez Arabidopsis / Function and regulation of Arabidopsis histone deacetylases in stress responseLei, Tingting 15 December 2017 (has links)
L'acétylation/désacétylation des histones joue un rôle important dans la régulation de divers processus du développement des plantes et de leur réponse au stress. Par contre, la régulation de l’activité des histone-desacétylases (HDAC) par des signaux cellulaires et la relation fonctionnelle entre les différentes HDAC au cours de la réponse au stress oxydatif et d'une élévation de la température ambiante restent encore mal connus. Mon travail de thèse a comporté : 1) l’analyse de la modification post-traductionnelle de la protéine HDA19, régulée par redox et celle des conséquences sur la régulation de l’expression de gènes et la réponse à l’acide salicylique (SA) ; 2) l'étude fonctionelle de HDA9, HDA15 et HDA19 dans la réponse à une élévation de la température ambiante. Dans la première partie, nous montrons que le changement redox induit par SA régule l’accumulation nucléaire de la protéine HDA19 via une S-nitrosylation réversible. Le traitement à SA, ou au donneur physiologique d’oxyde nitrique, S-nitrosoglutathione, augmente les marques d'acétylation des histones d'HDA19 dans des plantules d’Arabidopsis. Des lignées mutantes d’hda19 présentent un état plus oxydé avec une augmentation de l’expression de gènes associés au ROS/RNS, ainsi qu'une accumulation de nicotinamide adénine dinucléotide et de glutathionne. Ces résultats suggèrent que SA induit la S-nitrosylation d’HDA19, réduit son accumulation nucléaire et par conséquent augmente l’acétylation des histones. Dans la seconde partie, nous montrons que HDA9, HDA19 et HDA15 sont toutes impliquées dans la réponse de la plante à l’élévation de la température ambiante. Des mutants hda15 montrent une réponse constitutive à des températures élevées dans des conditions normales, alors que les mutants hda19 et hda9 ont des phénotypes insensibles à la température élevée. L’analyse de l’expression de gènes par RT-PCR et RNA-seq révèle que la mutation d’HDA15 provoque une augmentation de transcrits des gènes impliqués dans le métabolisme primaire et cellulaire lorsque les plantules sont transférées de 20°C à 27°C pendant 4 heures. Par contre, la mutation d’HDA19 conduit à l’induction de gènes impliqués dans des réponses au stress, alors que les gènes induits par la mutation d’HDA9 après le transfert à 27°C ne semblent pas concerner des catégories fonctionnelle spécifiques. Il semble donc que la réponse des plantes à l’élévation de la température soit régulées par HDA9 et HDA19 par différentes voies. Ces résultats suggèrent que de différents membres d’HDAC ont des rôles distincts ou opposés dans la réponse à l’élévation de la température, en affectant l’expression de gènes de différentes catégories. Les travaux de ma thèse apportent un éclairage nouveau sur la fonction des HDAC, en enrichissant la compréhension de la régulation de l’expression génique chez la plante. / Histone acetylation/deacetylation play important roles in a diverse range of developmental processes and stress-responsive pathways in plants. However, little is known regarding the regulation of HDACs themselves by environmental signals, which may alter their function in the regulation of gene expression. Also HDACs functions in plant sensing of environmental conditions such as redox stresses and warm ambient temperature need to be precized. My thesis work focuses on: (1) The analysis of redoxregulated posttranslational modifications and theirconsequences on HDA19 function in gene regulation and in salicylic acid (SA)-mediated stress response; (2) The study of the function of HDA9, HDA15, and HDA19 in plant responses to warm temperature and thermal-related genes expression. In the first part, we show that SA-induced redox changes negatively regulate HDA19 nuclear accumulation through a reversible S-nitrosylation. Treatment with SA, as well as with the physiological nitric oxide donor Snitrosoglutathione, increases the abundance of several histone acetylation marks of HDA19 in Arabidopsis seedlings. hda19 mutant lines display a more oxidative status with increased ROS/RNS-related genes expression, as well as nicotinamide adenine dinucleotide and glutathione levels. These results suggest that SA affects histone acetylation by decreasing the nuclear accumulation of HDA19, resulting in histone hyperacetylation. The second part of the study showed that HDA9, HDA15, and HDA19 are involved in modulating plant adaptation to higher ambient temperatures in Arabidopsis. Mutation of HDA15 displayed a constitutive warm temperatureresponsive phenotype under normal temperature, whereas HDA9 and HDA19 mutants were shown insensitive to warming-temperature. Genes expression and RNA sequencing analysis revealed that HDA15 mutation led to the up-regulation of many genes involved in primary and cellular metabolic process when the seedlings were transferred from 20 °C to 27 °C for 4 h. On the other hand, hda19 mutation resulted in up-regulation of genes mainly involved in stressresponses at both normal (20 °C) and warmer (27 °C) temperatures. However, up-regulated genes in hda9-1 mutants did not appear enriched for any particular gene functional category when shifted from 20 °C to 27 °C. Likely, HDA9 and HDA19 positively regulate thermosensory elongation through distinct mechanisms. Our study suggested that the dynamics of histone acetylation regulated by HDA9, HDA15, and HDA19 plays an important role for plant adaptation to warm temperature, which involves distinct regulatory pathways of gene expression. Taken together, my thesis work brought in a few new elements to the current understanding of HDACs functions in the regulation of gene expression in plants.
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Role of SABP2 in Systemic Acquired Resistance Induced by Acibenzolar-S-Methyl in Plants.Tripathi, Diwaker 13 August 2010 (has links) (PDF)
Plants have evolved an efficient mechanism to defend themselves against pathogens. Many biotic and abiotic agents have been shown to induce defense mechanism in plants. Acibenzolar-S-Methyl (ASM) is a commercially available chemical inducer of local and systemic resistance (SAR) response in plants. ASM functioning at molecular level is mostly unclear. This research was designed to investigate the mechanism of ASM action in plants. It was hypothesized that SABP2, a plant protein, plays an important role in ASM-mediated defense signaling. Biochemical studies were performed to test the interaction between SABP2 and ASM. Transgenic SABP2-silenced tobacco plants were used to determine the role of SABP2 in SAR induced by ASM. The expression of PR-1 proteins was used as a marker for SAR induction. Results showed that SABP2 converts ASM into acibenzolar that induces the expression of PR-1 proteins and develops the SAR response in ASM-treated plants.
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Characterization of the Pathway Leading to the Synthesis of Salicylic Acid in Plants Resisting Pathogen Infection.Eddo, Alexander 12 August 2008 (has links) (PDF)
Salicylic acid is a plant hormone that accumulates with plant-pathogen interaction. This accumulation corresponds to the plant being resistant to infection and without it the plant is susceptible. In this study, primers of genes involved in the normal synthesis of SA were used in RT-PCR to compare gene expression levels in susceptible and resistant plants challenged with tobacco mosaic virus. Because SA synthesis shares chorismate as a common substrate with the synthesis of aromatic amino acids, HPLC was used to determine whether the increase in SA could be attributed to a decrease in amino acid levels. The results suggest that genes of the shikimate pathway are up-regulated in both plant lines but much more quickly in the resistant plant, making differential gene expression a possible cause of SA accumulation. Additionally, results showed a more pronounced decrease in amino acid levels in resistant plants compared to susceptible plants.
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Synthesis of Novel Agrochemicals as Potential Plant Immunization Agents.Enyong, Arrey Besong 12 August 2008 (has links) (PDF)
The world's population is expected to grow from 6 billion to about 10 billion by 2050. The greatest population increase is expected to occur in Africa, Latin America, and Asia. To feed a world with huge increases in population and to sustain the well-being of humans, a large increase in food production must be achieved. The projected increase in food production must be accomplished on the existing cultivated areas because the expansion of new land is limited by environmental concerns, urbanization and increasing water scarcity.
Different compounds have been developed for the "immunization" of plants against several pathogens. These compounds induce systemic acquired resistance (SAR) in plants, leading to broad-based, long-lasting resistance to a wide range of pathogens. The salicylic acid binding protein 2 (SABP 2) has been identified as a key enzyme in the salicylic acid mediated pathogen resistance pathway, converting methyl salicylate (MeSA) to salicylic acid (SA), a key compound responsible for SAR . S-methyl benzo [1, 2, 3,] thiadiazole-7-carbothiate (BTH) was the first commercial compound used for plant immunization. We have synthesized and characterized some new salicylic acid derivatives [methyl-2-(2-hydroxy benzoyl thio) acetate and derivatives], and we have studied the in-vitro activity with SABP2 of BTH by HPLC analysis.
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Molecular Characterization of the Plant Hypersensitive Response and Maize Lesion Mimic MutantsRyan L Benke (14228987) 07 December 2022 (has links)
<p>The rapid localized cell death at and around sites of attempted pathogen infection, termed the hypersensitive response (HR), is an immune response mechanism commonly utilized in plants. This cell death limits pathogens from accessing host nutrients which often leads to resistance. The interaction of pathogen signals and host receptors that are required for the HR are well studied; however, the processes that regulate cell death during the HR remain enigmatic. The plant lesion mimic mutants, which form spontaneous lesions and/or undergo autoactive cell death in the absence of infection or stress, are commonly used as model systems to study the HR. Some lesion mimic mutants are caused by autoactive alleles of the resistance genes that recognize pathogen signals and trigger the HR. These mutants have facilitated studies of the HR as they allow the study of the HR without the need to control for pathogen infection. Currently, the etiologies of most maize lesion mimic mutants are unknown. Lesion mimic mutants contain numerous metabolic perturbations, including the increased accumulation of salicylic acid (SA), phenylalanine, and intermediates in heme and chlorophyll biosynthesis and catabolism. Some of these perturbations are dependent on the cause of lesion formation. As such, the accumulation of any of these metabolites in a lesion mutant may infer the etiology of that mutant. This dissertation contains three projects related to the molecular characterization of HR and maize lesion mimic mutants. In the first project (Chapter 2), I compared the metabolite profile of 23 maize lesion mimic mutants. This work identified two major findings that were further explored in the other projects in this dissertation. The first major finding is that four of the 23 mutants have metabolic perturbations that are like those of the known HR lesion mutant, <em>Rp1-D21</em>. In project two (Chapter 3), I molecularly characterize, <em>Lesion10</em>, which is one of the mutants that has HR-like metabolic perturbations. Using genome-wide association studies, I identified a gene candidate that may modify <em>Lesion10</em> phenotypic severity. The second major finding from project one is that SA accumulates to higher than wild-type levels in most of the lesion mutants analyzed. In the third project (Chapter 4), I characterized how SA is synthesized in maize and if SA is necessary or sufficient for the formation of lesions during the HR in maize. Using untargeted metabolite analysis, stable isotope feedings, and enzyme assays, I provide evidence of both known SA biosynthetic pathways in maize and demonstrate that the two pathways are interdependent. In addition, I show that increased accumulation of SA is not required for the HR in maize.</p>
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Understanding the role of SABP2-interacting proteins (SIP) 428: an NAD+-Dependent Deacetylase Enzyme in Abiotic Stress Signaling of Nicotiana tabacumOnabanjo, Mariam, Kumar, Dhirendra, PhD. 25 April 2023 (has links) (PDF)
Abiotic stresses like salinity, drought, and extreme temperature are constantly on the rise, posing a very high risk to global agricultural productivity and food security. Hence, understanding stress signaling pathways can help engineer plants that can better withstand stress in unfavorable conditions. The salicylic acid (SA) signaling pathway has been widely studied for its important role in mediating abiotic stress in plants. In tobacco plants, Salicylic Acid Binding Protein 2 (SABP2), a methyl esterase enzyme, catalyzes the conversion of methyl salicylate (MeSA) to SA, which triggers the defense response via the SA-mediated signaling pathway. SIP-428 (SABP2 Interacting Protein-428) is an NAD+ dependent SIR2-like (Silent Information Regulator) deacetylase enzyme that likely interacts with SABP2 during SA biosynthesis. In previous studies, SIP-428 has been shown to be a negative regulator of plant growth under abiotic stress (NaCl and mannitol in vivo). Reactive Oxygen Species (ROS) are oxidizing oxygen products that accumulate under stress conditions, and at high levels can be very harmful to plants. Antioxidant enzymes such as catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX), and superoxide dismutase (SOD) are actively involved in lowering the ROS levels in the cell by combating the oxidative stress. The objective of this study was to analyze the regulatory functions of SIP-428 in ROS signaling of tobacco plants through the biochemical quantification of POD and CAT activities. We investigated the SIP-428 RNAi-silenced tobacco plants for the POD and CAT enzyme activities in Osmotic (Mannitol) and Salinity (NaCl) stressed plants. Our results showed that SIP-428 plays a significant role in modulating antioxidant enzymes in stressed plants. This study has improved our understanding of some regulatory roles of SIP428, and its application can be used to enhance stress tolerance via the use of synthetic biology.
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Adsorption of Organic Contaminants from Aqueous Solution using BiocharEssandoh, Matthew 09 May 2015 (has links)
The main aim of this research is to provide a low cost and sustainable biochar for the removal of organic pollutants from aqueous solution. Wastewater pollution by organic contaminants of emerging concern has become a subject of intense discussion. Removing these contaminants from aqueous solution is paramount to improve water quality for both humans and animal consumption. Traditional adsorption techniques using activated carbon are universal and fast, however, they are very costly. This dissertation therefore seeks to find an alternative low cost adsorbent which can be used to adsorb contaminants from aqueous solution. In chapter one, an overview of some of the selected organic contaminants of emerging concern is given. Pharmaceutical and pesticide entry into the environment, their fate and ecotoxicity are highlighted. Available techniques for the removal of contaminants from aqueous solution are also given. Chapter two is a study on the adsorption of some selected pharmaceuticals using a fast pyrolysis low cost biochar produced from pinewood feedstocks. The pinewood biochar used as the adsorbent in this study was made by fast pyrolysis in an augered reactor at a temperature of 425 oC and a residence time of 20-30 s during bio-oil production. In chapter three, switchgrass biochar has been tested for its potential for remediating water that is contaminated with two phenoxy herbicides, 2,4-dichlorophenoxyacetic (2,4-D) acid and 2-methyl-4-chloro-phenoxyacetic acid (MCPA). The adsorption capacity was remarkable when compared to commercial activated carbon per unit of measured surface area. Furthermore, in chapter four, magnetic and non-magnetic low cost biochars have been tested for the removal of the herbicide metribuzin from aqueous solution under different experimental conditions. The magnetic biochar synthesized from raw switchgrass biochar does not show a detrimental effect on the adsorption capacity. Additional value of this magnetic biochar is the ease of separation from contaminated solution following adsorption.
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The Syntheses of Amino Substituted Salicylic Acids and Related CompoundsGerber, Martin 08 1900 (has links)
The introduction of the ether linkage into various compounds imparts physiological activity, hence the synthesis of various ether derivatives involving the phenol group seemed to be a possible route to tuberculostatic substances. The compounds reported in this work are to be tested for tuberculostatic properties by Parke, Davis and Company.
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