Plant Sciences Commons^™

Photosynthetic Acclimation To Warming And Elevated Co2 In Two Antarctic Vascular Plant Species, Vi Nt Bui

Electronic Thesis and Dissertation Repository

Climate change can affect the performance of the only two vascular plant species found in Antarctica, Deschampsia antarctica and Colobanthus quitensis. I investigated the response of these two species to warming and elevated CO₂ in terms of photosynthesis and leaf anatomy. While photosynthesis increased directly with rising temperature and CO₂, it showed no acclimation to changes in growth temperature, and a small degree of acclimation to growth under elevated CO₂. Likewise, leaf anatomy displayed little plasticity in response to changes in the growth environment, although D. antarctica’s stomatal groove structure was modified under …

Glucan Synthase-Like 8: A Key Player In Early Seedling Development In Arabidopsis, Behnaz Saatian

Electronic Thesis and Dissertation Repository

Plants’ cell walls have unique chemical composition and features which enable them to play essential roles during plant development as shaping the cells and providing intercellular communication between adjacent cells. Polysaccharides, including callose, and glycoproteins are known as the main constituents of the cell wall. Callose, a linear β-1,3-glucan polymer, is accumulated at the cell plate during cytokinesis, in plasmodesmata, where it regulates cell-to-cell communication, in dormant phloem, where it seals sieve plates after mechanical injury and pathogen attack, and in male and female gametophytes. GLUCAN SYNTHASE-LIKE (GSL) genes in Arabidopsis comprise a family of 12 members. A …

Inheritance, Differential Expression, And Candidate Gene Analyses For Avr2 In Phytophthora Sojae, Chelsea S. Ishmael

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Phytophthora sojae is an oomycete responsible for seed, root and stem rot of soybean plants. Managing this disease relies on growing soybean cultivars with race-specific resistance (Rps) genes that deliver complete host immunity in the presence of corresponding pathogen avirulence (Avr) effector proteins. The aims of this study were to characterize virulence towards Rps2 among different P. sojae strains, track the inheritance of this trait, and attempt to identify an Avr2 gene. Fifteen P. sojae strains were tested for virulence towards Rps2 and crosses were performed between selected virulent and avirulent strains to follow the inheritance of virulence. …

Functional Analysis Of The Mir156 Regulatory Network In Arabidopsis Siliques, Zhishuo Wang

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Siliques are photosynthetically active seed capsules and their development is strongly influenced by embryo development. MicroRNA156 (miR156)-SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) network is involved in regulating plant growth and development, but the downstream genes of this network are still not fully elucidated. Here, I show that the miR156/SPL2 pathway controls the development of floral organs, regulates pollen production, and thus affects male fertility in Arabidopsis thaliana. I present evidence that SPL2 binds to the 5’UTR of the ASYMMETRIC LEAVES 2 (AS2) gene in vivo, indicating that AS2 acts downstream of SPL2. When compared to wild-type plants, AS2 loss-of-function mutants …

Inferring Plastid Metabolic Pathways Within The Nonphotosynthetic Free-Living Green Algal Genus Polytomella, Sara Asmail

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The advent of photosynthesis facilitated the evolution of aerobic life on Earth. However, species such as Prototheca wickerhamii and Plasmodium falciparum, among many others, have lost photosynthesis and opted for a free-living/parasitic lifestyle. Despite this loss, these species have retained the plastid for its metabolic pathways, without which they would die. Polytomella is a nonphotosynthetic free-living alga, closely related to the photosynthetic model organism Chlamydomonas reinhardtii, and has been shown to lack a plastid genome. I set out to determine Polytomella plastid metabolic pathways using bioinformatics to look for mRNA and DNA homologous sequences matching pathway enzymes in model organisms. …

Planting The Chalcone Reductase Family Tree: Identification And Characterization Of Chalcone Reductase Genes In Soybean, Caroline Julia Sepiol

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Soybean (Glycine max [L.] Merr) is an important crop grown in Canada, generating $2.4 billion in sales. Though this number may be promising, soybean farmers lose about $50 million worth of yield annually due to root and stem rot disease caused by Phytophthora sojae. Many strategies have been developed to combat the infection; however, these methods are prohibitively expensive. A ‘cost effective’ approach to this problem is to select a trait naturally found in soybean that can increase resistance. One such trait is the increased production of root glyceollins. One of the key enzymes exclusively involved in glyceollin …

Genetic Analysis Of A Non-Germinating Mutant Of Arabidopsis Thaliana, Md Jakir Hossan

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Seed germination is partially controlled by plant hormone gibberellins (GAs). Chemical mutagenesis yielded an Arabidopsis thaliana mutant gm11, which has an absolute gibberellin requirement for seed germination. This mutant exhibited phenotypes of GA-rescuable dwarfs, including dark-green leaves, and reduced fertility. However, with repeated GA treatment, gm11 develops into fertile plants with a nearly wild type phenotype. Bulked-segregant analysis mapped gm11 to the bottom arm of chromosome 1, and subsequent next-generation mapping revealed that the mutation is a G → A transition in At1g79460 (GA2), creating a premature stop codon. This gene encodes an ent-kaurene synthase (KS) which catalyzes …

Ginsenosides, Glycosidases And The Ginseng-Pythium Interaction, Dimitre A. Ivanov

Electronic Thesis and Dissertation Repository

Ginsenosides, the triterpenoid saponins produced by American ginseng (Panax quinquefolius L.), have been extensively studied for their medicinal value, however, their function in the rhizosphere remains largely unknown. Like other saponins, ginsenosides possess mild fungitoxic activity toward some common ginseng pathogens. However, numerous oomycete root pathogens of ginseng, most notably Pythium irregulare Buisman, are able to partially deglycosylate the 20 (S)-protopanaxadiol ginsenosides Rb1, Rd and gypenoside XVII via extracellular glycosidases (ginsenosidases), leading to the formation of a common product, ginsenoside F2. In this thesis the potential role(s) of these extracellular ginsenosidases and the ginsenoside products they produce (ie. ginsenoside …

Functional Characterization Of P3n-Pipo Protein In The Potyviral Life Cycle, Hoda Yaghmaiean

Electronic Thesis and Dissertation Repository

Potyviruses represent the largest genus of plant-infecting viruses and include many agriculturally important viruses such as Turnip mosaic virus (TuMV), Soybean mosaic virus (SMV) and Plum pox virus (PPV). The potyviral genome consists of a large open reading frame (ORF) and a small ORF owing to a translational or transcriptional slippage in the P3 cistron. The polyproteins encoded by these two ORFs are proteolytically processed into 11 mature proteins. Recent studies have shown that P3N-PIPO, the frameshift resulting protein, is a plasmodesmata (PD)-located protein and involved in potyviral cell-to-cell movement by mediating the targeting of the potyviral CI protein to …

Identification Of Putative Plant Defense Genes Using A Novel Hydroponic Co-Cultivation Technique For Studying Plant-Pathogen Interaction, Naeem Nathoo

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Previous work on identifying the molecular mechanisms mediating plant-pathogen interactions and reciprocal host responses have little emphasis on developing models that closely resemble host-microbe interaction in planta. This work establishes an amalgamated model of interaction wherein successful pathogens elicit and overcome host defenses activated by microbial signatures and virulence factors. Using a hydroponic co-cultivation model, we assessed the responses of Arabidopsis thaliana Col-0 to Agrobacterium tumefaciens C58 to ameliorate limitations of previous approaches. Comparisons of differential gene expression between directly and indirectly affected host sites by microarray analysis revealed both reactive and pro-active defense responses, respectively. Selected homozygous single-gene …

Molecular Identification And Characterization Of Host Dead-Box Rna Helicases That Are Associated With Turnip Mosaic Virus Infection, Yinzi Li

Electronic Thesis and Dissertation Repository

Plant viruses have small and compact genomes whose coding capacity is not sufficient to fulfil the viral life cycle. Thus, they are largely dependent on the host by recruiting many host components such as proteins and membranes. Many efforts have been made towards understanding the role of host factors and recent progress has led to the identification and characterization of a number of important host factors recruited for plant virus replication. DEAD-box RNA helicases (RHs) have been shown to play multiple roles in RNA metabolism, including remodeling RNA structures and promoting RNA-protein association/dissociation. During viral replication, RHs are implicated in …

Effects Of Growth Temperatures And Elevated Co2 On Respiration Rates In Norway Spruce, Yulia Kroner

Electronic Thesis and Dissertation Repository

Projected increase in growth temperatures and CO₂ may affect carbon balance in Norway spruce (Picea abies), a dominant coniferous species of the boreal forest ecosystem. To examine this, I exposed three-year-old Norway spruce seedlings to six treatments: ambient (400 ppm) and elevated (750 ppm) CO₂ concentrations combined with three growth temperatures: ambient, ambient +4 ^oC, and ambient +8 ^oC. I found that while net growth was generally not affected by growth CO₂ or temperature, leaf nitrogen concentrations were reduced, mortality rates were higher, and needles were shorter and thinner in +8 ^oC …

Soybean Isoflavonoid Biosynthesis: Constituents And Circumstance At The Transcriptomic And Molecular Levels, Mehran Dastmalchi

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Isoflavonoids are specialized metabolites, almost exclusive to the legume family of plants. They are actors in symbiosis with nitrogen-fixing bacteria and in plant stress response. Isoflavonoids are noted for their human health benefits. Isoflavonoid content in legumes has proven to be a complex trait. The goal of the present research is to determine the mechanisms underlying isoflavonoid biosynthesis in soybean.

The first approach was to unravel the genetic factors of isoflavonoid biosynthesis. A branch-point enzyme of the phenylpropanoid pathway, chalcone isomerase (CHI), catalyzes the reaction producing flavanones, the nucleus for many downstream metabolites such as isoflavonoids. I identified twelve soybean …

Inheritance Of Virulence In The Root Rot Pathogen Phytophthora Sojae, Sirjana Devi Shrestha

Electronic Thesis and Dissertation Repository

The oomycete Phytophthora sojae causes stem and root rot of soybean plants. The interaction of pathogen avirulence (Avr) and host resistance (R)-genes determine the disease outcome. The Avr3a mRNA transcript level is variable among P. sojae strains and determines virulence towards the R-gene Rps3a. To study the inheritance of virulence, genetic crosses and self-fertilizations were performed. A cross between P. sojae strains ACR10 and P7076 causes transgenerational gene silencing of Avr3a allele, and this effect is meiotically stable up to the F₅ generation. However, test-crosses of F₁ (Avr3a^ACR10/Avr3a …

Effect Of Photoperiod On Redox Regulation Of Phenotypic Plasticity And Cellular Growth In Chlorella Vulgaris, Lauren E. Hollis

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Photoautotrophs are predisposed to maintain a balance between light energy absorption with the capacity to consume this energy through metabolism. An imbalance in energy flow may be a consequence of increased light intensity and is sensed as modulation of excitation pressure (EP). Chlorella vulgaris acclimated to continuous high EP exhibits a yellow-green phenotype characterized by reduced chlorophyll content and high chlorophyll a/b ratio with reduced light-harvesting complex abundance relative to the dark green phenotype of low EP-acclimated cultures. Previous studies on acclimation to EP in green algae have been conducted under constant growth light. To determine the role of EP …

Thylakoid Phosphorylation And Cell Morphology In The Antarctic Psychrophile, Chlamydomonas Sp. Uwo241, Beth Szyszka-Mroz

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The unicellular green microalga, Chlamydomonas sp. UWO 241, was isolated from Lake Bonney, Antarctica. A unique characteristic of this algal strain is its inability to undergo state transitions combined with an altered thylakoid protein phosphorylation profile, which suggests the absence of LHCII phosphorylation, and preferential phosphorylation of a set of novel proteins. Examination of the unique phosphoproteins revealed that they are associated with a large pigment-protein supercomplex, which contains components of both photosystem I and the cytochrome b₆/f complex and likely functions in cyclic electron flow (CEF).

The absence of phosphorylation of LHCII proteins, associated with state …

Arabidopsis Chromatin Remodeler Brahma: Its Functional Interplay With Polycomb Proteins And The Ref6 Histone Demethylase, Chenlong Li

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BRAHMA (BRM) is a SWI/SNF-type chromatin remodeling ATPase that plays an important role in regulation of gene expression. Tri-methylation of lysine 27 on histone H3 (H3K27me3) is a histone modification that is associated with transcriptionally repressed genes and catalyzed by Polycomb Group (PcG) proteins. BRM has been proposed to antagonize the function of PcG proteins but the underlying molecular mechanism is unclear. To understand how BRM regulates the function of PcG proteins during plant development, a genome-wide analysis of H3K27me3 in brm mutant was performed using chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq). Loss of BRM leads to increased …

Protein Body Biogenesis And Utility In Recombinant Protein Production In Nicotiana Benthamiana, Reza Saberianfar

Electronic Thesis and Dissertation Repository

Protein bodies (PBs) are endoplasmic reticulum (ER) derived organelles found in seeds whose function is to accumulate seed storage proteins. It was shown that PB formation is not limited to seeds, and green fluorescent protein (GFP) fused to either elastin-like polypeptide (ELP), hydrophobin-I (HFBI) or Zera^® fusion tags induces PBs in leaves of Nicotiana benthamiana. The mechanism by which fusion tags induce PBs is not well understood. To address how PBs form and develop in plant leaves, I studied the factors involved in their formation including recombinant protein concentration, effect of the fusion tags, PB sequestration patterns and …

Two Spotted Spider Mite (Tetranychus Urticae) Selection To Arabidopsis Thaliana, Huzefa Ratlamwala

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Spider mite feeding on A. thaliana induces the production of indole glucosinolates (IGs), plant secondary metabolites that negatively affect mite performance. In this study I conducted selection experiments on A. thaliana with varying levels of IGs, to determine if mites could adapt to IGs and other defense compounds. After 12 months, mites reared on host with IGs performed significantly better on A. thaliana than mites maintained on beans. However, an adaptation cost was detected between selected mite lines and their ancestral host. The qRT-PCR data on different mite lines revealed that the detoxification genes previously identified may only be involved …

Identification And Characterization Of Cysteine Protease Genes In Tobacco For Use In Recombinant Protein Production, Kishor Duwadi

Electronic Thesis and Dissertation Repository

Plants are an attractive host system for pharmaceutical protein production. Many therapeutic proteins have been produced and scaled up in plants at a low cost compared to the conventional microbial and animal based systems. The main technical challenge during this process is to produce sufficient level of proteins in plants. Low yield is generally caused by proteolytic degradation during expression and downstream processing of recombinant proteins. The yield of a human therapeutic protein interleukin (IL) -10 produced in transgenic tobacco leaves was found to be below the critical level, and is potentially due to degradation by tobacco cysteine proteases (CysPs). …

Functional Analysis Of Two Brassinosteroid Responsive, Putative Calmodulin-Binding Proteins 60 (Cbp60s) In Arabidopsis Thaliana, Purvikalyan Pallegar

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Brassinosteroids (BRs) have remarkable ability to increase stress tolerance in plants. Investigations to understand the molecular mechanisms underlying BR-mediated stress tolerance resulted in identification of genes belonging to the family calmodulin binding protein X (CBPX). The present study was focused on studying the role of CBPX1 and CBPX2 in BR mediated stress tolerance and functional characterization using a reverse genetic approach. The upregulation of CBPX1 and CBPX2 by BR and stress noted in publicly available AtGenexpress datasets and by qRT-PCR analysis strongly suggests that these are BR responsive genes and functional analysis of T-DNA insertion mutants showed salt stress related …

The Effects Of Ocean Acidification And Eutrophication On The Growth, Lipid Composition And Toxicity Of The Marine Raphidophyte Heterosigma Akashiwo., Julia Rose Matheson

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Anthropogenic forcing, such as ocean acidification caused by rising carbon dioxide emissions, and eutrophication due to increased nutrient loadings in run-off, are causing major changes to the biogeochemistry of the oceans. As a consequence, coastal phytoplankton are susceptible to altered biogeochemical environments. This study examined the effect of a lower pH and increased levels of nutrients on the common coastal harmful alga, Heterosigma akashiwo. Growth rates, maximal cell yields, neutral lipid accumulation and toxicity of cells grown under various pH and nutrients regimes were measured. H. akashiwo growth was near maximal when grown at lower pH levels. There was …

Growth Of The Marine Fish-Killing Phytoflagellate, Heterosigma Akashiwo Under Emerging Coastal Regimes: Temperature, Eutrophication And Ocean Acidification, Cayla M. Bronicheski

Electronic Thesis and Dissertation Repository

Coastal oceans are fundamental to human economies, nutrition and recreation. Anthropogenic stressors have led to the acceleration of the nitrogen cycle, the accumulation of inorganic carbon in the earth’s atmosphere, the loss of UV-scavenging upper atmospheric ozone and the overall accumulation of deep elements from the earth’s crust to surface exposure. These changes have caused ocean acidification and eutrophication events in coastal waters and the impacts of these events on primary production and ocean biodiversity are not yet fully understood.

This study examined the effects of predicted future ocean conditions (salinity, temperature, reduced seawater pH and modified nitrogen supplies), on …

Characterization Of The Alternative Oxidase From The Psychrophilic Green Alga Chlamydomonas Sp. Uwo241, Michael Sj Inman

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The alternative oxidase (AOX) was studied in the psychrophilic green alga Chlamydomonas sp. UWO241. AOX is the sole component of the alternative pathway of mitochondrial electron transport and is present in all plant and algal species. In silico analysis of the deduced protein sequence of the cloned AOX cDNA showed that the UWO241 protein has lower amounts of proline and higher amounts of lysine and tryptophan compared to the AOX sequence of the mesophilic alga C. reinhardtii. These changes have been seen in other studies of cold-adapted enzymes. Interestingly, unlike C. reinhardtii, AOX transcript abundance in UWO241 …

Effects Of Excitation Pressure On Variegation And Global Gene Expression In Arabidopsis Thaliana, Rainer Bode

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I assessed the effects of photosystem II excitation pressure on chloroplast biogenesis and leaf sectoring in the Arabidopsis thaliana variegated mutants im, spotty, var1, var2, chs5 and atd2. The plants were grown under varying degrees of excitation pressure induced by growth at increasing irradiance at different temperatures and the extent of variegation was quantified throughout the plant’s development. I found that the degree of variegation was positively correlated with excitation pressure, regardless of whether high light or low temperature was used to induce increased excitation pressure in all the mutants tested. This was irrespective of …

Increasing Atmospheric Nitrogen Deposition: Implications For Tallgrass Prairie Restoration, Jennifer M. Mcphee

Electronic Thesis and Dissertation Repository

Continued intensification of agriculture and combustion of fossil fuels will increase rates of atmospheric nitrogen (N) deposition over the next century. N is typically a limiting resource for terrestrial plants, and many species are adapted to low-N conditions. Increased N availability can affect both plant biomass and species composition, often favouring N-demanding, adventive species. These effects can be adverse in the context of ecological restoration, where the end product often relies on establishing a particular community composition. I used a field experiment in Norfolk County, Ontario, to examine how N addition affects species composition and plant productivity of a tallgrass …

Heterologous Production And Characterization Of Cell Wall Degrading Enzymes Using Plants As A Bioreactor, Eridan Orlando Rodrigues Pereira

Electronic Thesis and Dissertation Repository

Plants are wonderful living organisms. They are able to store solar energy into carbohydrates by fixing CO₂ through photosynthesis which can be subsequently harvested and used for fuel production. However, one of the major limitations for transforming these carbohydrates into liquid fuels is the recalcitrance of the plant cell wall. Although microorganisms have evolved a series of cell wall degrading enzymes to harvest efficiently this energy and are considered the main source of these biocatalysts, harnessing these microorganisms for the production of enzymes is a costly process and a major factor limiting the commercialization of lignocellulosic biomass-to-ethanol processes. The …

Expression Analysis Of Histone Acetyltransferases In Rice Under Drought Stress, Hui Fang

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Histone acetylation is one of the vital reversible modifications in eukaryotes. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) maintain the homeostasis of histone acetylation. HATs are associated with genome-wide transcriptional activation and various biological processes in response to various stresses. Drought stress causes a range of physiological and biochemical responses in plants. Eight HATs which belong to four different families (CBP, GNAT, MYST, and TAFII250 family) have been identified in rice. In this research, four OsHATs, one from each family, were chosen based on in silico domain and promoter analysis. The real-time qPCR analysis demonstrated that drought stress caused …

Characterization Of A Putative Activation Domain In The Hulk Gene Family, Christopher Doan

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The HULK gene family participates in regulation of both flowering time and development in the plant Arabidopsis thaliana. The proteins encoded by these genes share conserved domain structures including a proline-rich region (PRR) in the carboxyl-terminus. Based on sequence analysis and the presence of a proline-rich domain, it has been suggested that the HULKs are putative transcription factors in which HUA2 is known to regulate several late-flowering genes: FLC, FLM and MAF2.

To investigate the putative transcriptional activation domain in the carboxyl-terminus of the HULKs, full-length HULKs and deletion constructs were 3-AT titrated in yeast-one hybrids. It …

Absence Of Phosphoenolpyruvate Carboxylase Atppc3 Increases Sensitivity Of Arabidopsis Thaliana To Cadmium, Ian R. Willick

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Phosphoenolpyruvate carboxylase (PEPC) and PEPC kinase (PPCK) catalyze a reaction feeding into the tricarboxylic acid (TCA) cycle, increasing the production of metal-chelating organic acids. Little research has been conducted on PEPC isoenzymes in Cd-stressed plants. Arabidopsis (Arabidopsis thaliana) wild-type and AtPPC1 – AtPPC3 mutants, each lacking one of three PEPC isoenzymes, grown in 0, 1, or 5 µM CdCl₂ were smaller and had increased AtPPC1 – AtPPC3 and AtPPCK1 – AtPPCK2 transcript abundance, relative phosphorylation, and PEPC activity, more so in roots than shoots. Concentrations of oxaloacetate, citrate and total organic acids increased with greater CdCl_{2 …}