Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on Sept. 12, 2006). PDF text of dissertation: 155 p. : ill. ; 0.88Mb. UMI publication number: AAT 3208083. Includes bibliographical references. Also available in microfilm, microfiche and paper format.

No description available.

Plants have evolved a plethora of effective mechanisms to protect themselves from biotic stresses. Jasmonates (JAs) are employed as vital defence signals against both insect and pathogen attack. Jasmonic acid (JA) signalling plays a central role in plant defence and development. S-nitrosylation, a redox-based post-translational modification plays an important role in plant disease resistance. S-nitrosoglutathione (GSNO) is formed by the reaction of antioxidant glutathione (GSH) and nitric oxide (NO) and acts as a mobile reservoir of NO bioactivity. The Arabidopsis thaliana S-NITROSOGLUTATHIONE REDUCTASE (AtGSNOR1) controls multiple modes of disease resistance via S-nitrosylation. In this context, the Arabidopsis lossof- function mutant atgsnor1-3 exhibits higher susceptibility to Botrytis cinerea a necrotrophic pathogens and Pieris rapae insect attack. Accumulation of JA was reduced in atgsnor1-3 after mechanical wounding. JA marker genes were also downregulated in atgsnor1-3 compared to Col-0 after Methyl Jasmonate (Me-JA) treatment. The relative gene expression of Vegetative Storage Protein (VSP) was reduced in atgsnor1-3 compared to wild type. Further, protein-protein interaction experiments in yeast two hybrid assays revealed an inhibition of Coronatine-insensitive 1 (COI1) and Jasmonate ZIM domain (JAZ1) interactions upon NO donor application. Interestingly it was also shown that Nitric oxide donor may inhibited the degradation of JAZ1-β-glucoronidase (GUS) fusion protein driven by a CaMV35s:: JAZ1-GUS transgene in GUS histochemical analysis but not in flurometric assay. A biotin switch assay of recombinant JAZ1-Maltose-binding protein (MBP) has shown that JAZ1-MBP was S-nitrosylated and mass spectrometry suggested Cysteine229 (Cys229) was the site of this modification. Further, CaMV35S::JAZ1-Flag transgene expressed in either a wild-type or atgsnor1-3 genetic background, suggested that JAZ1 was S-nitrosylated in vivo. Collectively, our data imply that JA-signalling engaged in response to either insect predation or attempted B. cinerea infection is under redox control as high SNO in atgsnor1-3 has disrupted the JA signalling pathway. Furthermore, our data suggest that S-nitrosylation of Cys-229 of JAZ1 may control JA-mediated signalling by blocking the interaction of this protein with COI1, thus reducing the turnover of JAZ1 by the 26S proteasome and consequently enabling continued JAZ1-mediated repression of JA-dependent gene expression in the presence of Me-JA. Thus our findings highlight the importance of NO and associated S-nitrosylation in JA signalling during plant immune response.

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains x, 101 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 81-101).

No description available.

All organisms require rapid and flexible signaling mechanisms in order to effectively respond to biotic and abiotic stress. Calcium ions (Ca2+) have proven to be important components of signaling networks. Observations of stimulus-specific oscillations of cytosolic Ca2+ during signal transduction suggest that Ca2+ signals directly encode information. These stimulus-specific oscillations, known as Ca2+ signatures, can be interpreted by an array of Ca2+-binding sensors and effectors, which subsequently regulate appropriate cellular responses. While progress has been made regarding the classic Ca2+-sensor calmodulin (CaM), less research has been directed towards the CaM-like family of Ca2+-sensors (CMLs). This family – unique to plants – is suspected to regulate a multitude of stress and developmental pathways; however, to date very few members of this family have had their functions elucidated by the identification of downstream targets and upstream regulators. In the present study, I investigate the regulation of CML39, which has previously been shown to strongly respond to the stress hormone jasmonic acid (JA) in Arabidopsis. Bioinformatic tools predict a large number of putative JA-responsive cis-elements within the CML39 promoter. Deletion analysis of CML39 promoter fragments in planta reveals that some cis-elements respond in a tissue-specific manner. Analysis of transgenic MYC2 loss-of-function (myc2) mutants demonstrates that MYC2 – the preeminent JA-responsive transcription factor – is not necessary for CML39 promoter activity. Collectively, these data reveal a complex tissue-specific pattern of CML39 regulation and provide a foundation for the future identification of relevant transcription factors. / Thesis (Master, Biology) -- Queen's University, 2013-09-24 21:06:30.592

Nutrition of host plants has been shown to have a direct effect on the productivity of numerous insect pests, including western flower thrips [(WFT) Frankliniella occidentalis (Pergande)] – a major pest on both horticulture and agronomic crops. Plants use constitutive and induced chemical defenses to aid in protection against phytophagous insects. Reductions in WFT abundance in response to decreased nutrient availability has been attributed to the reduced availability of nutrients required for WFT productivity. The goals of this research were to determine the effects of fertilization on chemical defenses, and subsequent effects on WFT feeding and abundance. More importantly, the effects of fertilization and WFT feeding on plant growth, development, physiology, and quality were determined to assess the viability of optimizing fertilization in order to increase host plant resistance in gerbera. Constitutive (i.e. phenolics) and induced (i.e. jasmonic acid) chemical defenses were enhanced when fertilization was reduced. Reducing fertilization increased the total phenolics and wound- and WFT-induced jasmonic acid (JA) accumulation in gerbera. The enhanced chemical defenses in lower fertility plants resulted in reduced WFT abundance and feeding damage. These results indicate that the strategy for some plant species under nutrient stress is to increase constitutive defenses, while maintaining, or possibly increasing inducible defenses instead of growth. Similar to 0X fertility plants (only supplied with initial fertilizer charge in commercial media), 0.3X (received 30% of recommended rate) gerberas had reduced biomass and greater chemical defenses compared to 1X plants, but these plants did not appear to be nutritionally stressed—and 0.3X plants without WFT were rated as marketable. Reducing fertilization by 70% (0.3X) did not affect flower dry mass (DM) or the rate of flowering, but the flower stalks (peduncles) were taller in response to the fertilizer reduction. Hence, reducing fertilization to a moderate level in gerbera production may reduce susceptibility to WFT, while producing marketable crops.

Thesis (Ph.D.)--Michigan State University. Biochemistry and Molecular Biology, 2008. / Title from PDF t.p. (viewed on July 7, 2009) Includes bibliographical references. Also issued in print.

Plants synthesize a diverse array of phytochemicals in response to interactions with herbivores, pathogens, and commensal microbes. These phytochemicals may simultaneously enhance crop defense and quality, representing a potential pest management strategy. However, plant chemical responses to different types and levels of biotic interactions remain unclear, particularly in fruit tissues, and the feasibility of inducing these defenses through elicitor application in field environments also requires further examination. Thus, apples were used to 1) examine the impact of distinct communities of biotic interactions among plants, insects, and microbes on fruit phenolic chemistry, and 2) examine the impact of the phytohormones jasmonic acid (JA), salicylic acid (SA), and melatonin (M) on fruit phenolic chemistry and resistance against pests and pathogens. Ultimately, phenolic defenses were induced by fungal damage primarily in ripe pulp tissues, where there was also a positive relationship between fungal endophyte and phenolic diversity, supporting a broad hypothesis that chemical diversity may increase with biotic diversity. Additionally, two compounds were upregulated in response to fungal damage: chlorogenic acid and an unidentified benzoic acid. Elicitor applications did not affect phenolic chemistry, but the combined application of JA-SA analogues had some chemical or physical effect, as this treatment reduced emergence of the insect Rhagoletis pomonella. Thus, fruit induced defenses may be tissue-specific and subject to temporal, environmental, or genotypic variation. Overall, these chapters examined the relationship between biotic interactions and induced fruit chemistry, with the goal of improving understanding of plant-microbe-insect interactions and incorporating these interactions into more sustainable agricultural practices. / Master of Science / Plants may produce a diverse array of defensive phytochemical compounds in response to interactions with herbivores, pathogens, and the microorganisms that reside within plant tissues. These phytochemicals may simultaneously improve crop defenses and quality, representing a potential agricultural management strategy. However, plant chemical responses to different types and levels of biotic interactions are not well-understood, particularly in fruit tissues, and the feasibility of activating these defenses in fruits through the application of phytohormones that regulate defense pathways as a potential management strategy also requires further examination. Thus, apples were used to 1) examine the impact of distinct communities of biotic interactions among plants, insects, and microbes on fruit chemistry, focusing on phenolics, an important class of phytochemical compounds, and 2) examine the impact of the defense-activating phytohormones jasmonic acid (JA), salicylic acid (SA), and melatonin (M) on fruit phenolic chemistry and resistance against pests and pathogens. Ultimately, phenolic defenses were activated by fungal damage primarily in ripe pulp tissues, where there was also a positive relationship between fungal endophyte and phenolic diversity, supporting a broad hypothesis that chemical diversity may increase with biotic diversity. Additionally, two compounds were produced in response to fungal damage: chlorogenic acid and an unidentified benzoic acid. Phytohormone applications did not affect phenolic chemistry, but the application of the combined JA-SA analogues had some chemical or physical effect, as this treatment reduced emergence of the insect Rhagoletis pomonella. Overall, the phytochemical defenses activated by biotic interactions in fruits may occur primarily in certain tissue types, and may also vary due to environmental conditions, time of year, or plant species. These chapters examined the relationship between fruit chemistry and biotic interactions with the goal of improving understanding of plant-microbe-insect interactions and incorporating these interactions into more sustainable agricultural practices.

Pathogen-associated molecular pattern (PAMP) recognition occurs by plasma membrane located receptors that induce among other processes nuclear gene expression. The plant FLS2-BAK1 receptor complex binds the bacterial PAMP, flg22 and induces a series of defense responses. The resulting signal transduction events occur through the activation of two MAPK signaling cascades, which trigger a rapid and strong activation of MPK3, MPK4 and MPK6. Cellular responses to pathogens are regulated by the activated MAPKs, which lead to the eventual phosphorylation of cytoplasmic and nuclear substrates. These MAPK substrates in turn respond to phosphorylation by reprogramming the expression of defense genes. A large scale phosphoproteomics screen of nuclear proteins in wild type and mpk mutant plants in response to flg22 revealed several novel putative targets of MAP kinases. This thesis is aimed at identifying the role of two of these chromatin associated proteins in plant immunity and their signaling mechanisms. The chromatin associated proteins we chose to study here are LITTLE NUCLEI/CROWDED NUCLEI (LINC/CRWN), LINC1 and the AT-HOOK MOTIF CONTANING NUCLEAR LOCALIZED 13 (AHL13) proteins. We demonstrate that these two chromatin associated proteins play a positive regulatory role in jasmonic acid signaling and immunity. Knock out mutants for both genes exhibit impairment in early and late innate immune reposes to both PAMP and hemibiotrophic pathogen strains. We also demonstrate that these mutants are compromised in regulating the expression of genes involved in jasmonic acid (JA) signaling and responses and genes involved in the biosynthesis both the indole and aliphatic glucosinolate (GS) pathways. Moreover, Pst DC3000 hrcC triggers JA and JAIle accumulation in these mutants, whereas salicylic acid (SA) levels are unchanged. We were also able to identify and validate two novel MAPK targeted phosphosites in AHL13 that affect the protein stability of AHL13 and we establish its role as a MPK6 substrate that affects jasmonic acid biosynthesis and PTI responses. Together this work identifies two novel signaling components involved in the regulation of jasmonic acid homeostasis and immunity.