Digital Commons Network^™

Editorial: Structure And Function Of Chloroplasts, Volume Iii, Hongbo Gao, Alistair J. Mccormick, Rebecca Roston, Yan Lu

Department of Biochemistry: Faculty Publications

Chloroplasts are endosymbiotic organelles derived from cyanobacteria. They have a double envelope membrane, including the outer envelope and the inner envelope. A complex membrane system, thylakoids, exists inside the chloroplast. It is the site of the light-dependent reactions of photosynthesis. The stroma is the main site of the carbon fixation reactions. Although photosynthesis is a very complicated process with many proteins involved, there are many other important processes that occur in chloroplasts, including the regulation of photosynthesis, the biogenesis and maintenance of the structures, carbohydrate, lipid, tetrapyrrole, amino acid, and isoprenoid metabolism, production of some phytohormones, production of specialized metabolites, …

Regulation Of Plasmodesmata By Specialized Metabolites Glucosinolates In Arabidopsis Thaliana, Jessica C. Fernandez

Doctoral Dissertations

Communication is an essential component to all living organisms. In

plants, the additional cell wall surrounding each cell adds a layer of complexity

not observed in animals. To overcome the literal wall separating cells, plants

have evolved specialized pores to connect adjacent cells. Plasmodesmata (PD)

allow plants to have a continuous cytoplasm between cells. Although

plasmodesmata may appear simple and lack regulation, their structural

components and their regulatory machinery is complex and not well understood.

Organelle-to-nucleus-to-plasmodesmata signaling (ONPS) have been worked as

a leading model for a possible regulatory mechanism. Many of the details of

organelle-to-nucleus retrograde signaling pathways have …

Iojap: Morphological And Physiological Phenotype Characterization In Arabidopsis, Thomas Jay Payne

Doctoral Dissertations

IOJAP protein is found in all organisms that contain a ribosome of bacterial origin. The majority of studies suggest that IOJAP plays a role in translation, although this has yet to be thoroughly investigated in plants. Using Arabidopsis thaliana, an extensive phenotype characterization of iojap mutants was performed. Many processes of plant growth were slightly impaired at optimal temperature (22˚C) but became severely hindered at low temperature (12˚C and 4˚C). These cold temperature defects manifested in an overall reduction of plant growth as well as variegation, chlorosis, leaf hyponasty, as well as reduced maximum quantum yield (F_v/F …

Editorial: Structure And Function Of Chloroplasts - Volume Ii, Yan Lu, Lu Ning Liu, Rebecca L. Roston, Jurgen Soll, Hongbo Gao

Department of Biochemistry: Faculty Publications

No abstract provided.

A Bioinformatic Approach To Exploring Land Plant Evolution, Lauren Margaret Orton

Graduate Research Theses & Dissertations

Today, researchers are inundated with an overwhelming amount of data due to advances in DNA sequencing technologies. This has benefited the fields of both bioinformatics and phylogenomics substantially. With the ability to increase sampling at both the taxonomic and molecular levels, we are now able to produce robust phylogenomic reconstructions and better discern relationships between taxa.

The goals of this dissertation are in two distinct parts: 1) to advance the understanding of land plant terrestrialization and evolution through examination of the closest relative to the land plant lineage, a species of green algae; and 2) to explore evolution among a …

Toward Understanding The Mechanism Of Protein Targeting In The Chloroplast Signal Recognition Particle Pathway, Mercede Furr

Graduate Theses and Dissertations

Protein targeting is a vital cellular function. The signal recognition particle (SRP) pathway is a universally conserved targeting system present in the cytosol and used to co-translationally target many proteins to the inner membrane of prokaryotes and the endoplasmic reticulum of eukaryotes. The chloroplast has a homologous SRP system which post-translationally targets light harvesting chlorophyll binding proteins (LHCPs) to the thylakoid membrane for integration. The chloroplast SRP (cpSRP) is a heterodimer with a 54 kDa subunit equivalent to SRP54 in the canonical pathway. In addition, cpSRP contains a novel 43 kDa subunit which is a unique and irreplaceable component. cpSRP43 …

An Arabidopsis Protoplast Isolation Method Reduces Cytosolic Acidification And Activation Of The Chloroplast Stress Sensor Sensitive To Freezing 2, Allison C. Barnes, Christian G. Elowsky, Rebecca Roston

Department of Biochemistry: Faculty Publications

Chloroplasts adapt to freezing and other abiotic stresses in part by modifying their membranes. One key-remodeling enzyme is SENSITIVE TO FREEZING2 (SFR2). SFR2 is unusual because it does not respond to initial cold stress or cold acclimation, instead it responds during freezing conditions in Arabidopsis. This response has been shown to be sensitive to cytosolic acidification. The unique lipid products of SFR2 have also been detected in response to non-freezing stresses, but what causes SFR2 to respond in these stresses is unknown. Here, we investigate protoplast isolation as a representative of wounding stress. We show that SFR2 oligogalactolipid products accumulate …

Lipid Transport Required To Make Lipids Of Photosynthetic Membranes, Evan Labrant, Allison C. Barnes, Rebecca Roston

Department of Biochemistry: Faculty Publications

Photosynthetic membranes provide much of the usable energy for life on earth. To produce photosynthetic membrane lipids, multiple transport steps are required, including fatty acid export from the chloroplast stroma to the endoplasmic reticulum, and lipid transport from the endoplasmic reticulum to the chloroplast envelope membranes. Transport of hydrophobic molecules through aqueous space is energetically unfavorable and must be catalyzed by dedicated enzymes, frequently on specialized membrane structures. Here, we review photosynthetic membrane lipid transport to the chloroplast in the context of photosynthetic membrane lipid synthesis. We independently consider the identity of transported lipids, the proteinaceous transport components, and membrane …

The Mystery Of Nuclear Localization Of Arogenate Dehydratase5 From Arabidopsis Thaliana, Sara Abolhassani Rad

Electronic Thesis and Dissertation Repository

Arogenate dehydratases (ADTs) have been identified to catalyze the last step of phenylalanine (Phe) biosynthesis in plants. All ADTs have a transit peptide sequence that targets them into the chloroplasts where the biosynthesis of Phe happens. Subcellular localization studies using fluorescently tagged Arabidopsis thaliana ADTs demonstrated that all six ADTs localize to chloroplast stromules (stroma filled tubules). However, one member of this family, ADT5, was also detected in the nucleus. As dual targeting of proteins to different cell compartments is an indication of multifunctionality, ADT5 nuclear localization suggests that this member of the ADT protein family is a moonlighting protein …

Decoding The Cellular Zipcode: Functional Analysis Of Transit Peptide Motifs And Mechanistic Implications In Plastid Targeting And Import, Kristen N. Holbrook

Doctoral Dissertations

Eukaryotic organisms are defined by their compartmentalization and various organelles. The membranes that define these organelles require complex nanomachines (known as translocons) to selectively mediate the import of proteins from the cytosol where they are synthesized into the organelle. The plastid, (specifically the chloroplast) which is characteristic of plant cells, possibly represents the most complex system of protein sorting, requiring many different translocons located in the three membranes found in this organelle. Despite having a small genome, the vast majority of plastid-localized proteins are nuclear-encoded and must be post-translationally imported from the cytosol. These proteins are encoded as a larger …

Synthesis And Transfer Of Galactolipids In The Chloroplast Envelope Membranes Of Arabidopsis Thaliana, Amélie Kelly, Barbara Kalisch, Georg Hölzl, Sandra Schulze, Juliane Thiele, Michael Melzer, Rebecca L. Roston, Christoph Benning, Peter Dörmann

Department of Biochemistry: Faculty Publications

Galactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol

(DGDG)] are the hallmark lipids of photosynthetic

membranes. The galactolipid synthases MGD1 and DGD1

catalyze consecutive galactosyltransfer reactions but localize to the

inner and outer chloroplast envelopes, respectively, necessitating

intermembrane lipid transfer. Here we show that the N-terminal

sequence of DGD1 (NDGD1) is required for galactolipid transfer

between the envelopes. Different diglycosyllipid synthases (DGD1,

DGD2, and Chloroflexus glucosyltransferase) were introduced into

the dgd1-1 mutant of Arabidopsis in fusion with N-terminal extensions

(NDGD1 and NDGD2) targeting to the outer envelope. Reconstruction

of DGDG synthesis in the outer envelope membrane was

observed only with diglycosyllipid synthase fusion …

Ubiquitin Goes Green, Zhihua Hua, Richard D. Vierstra

Biology Faculty Publications & Presentations

Chloroplasts depend on the nucleus for much of their proteome. Consequently, strong transcriptional coordination exists between the genomes, which is attuned to the developmental and physiological needs of the organelle. Recent studies highlight that the post-translational modifier ubiquitin adds another layer to plastid homeostasis and even helps eliminate damaged chloroplasts.

The Mechanism Of Lhcp Insertion Into Thylakoid Membranes, Larae Brown

Graduate Theses and Dissertations

The light harvesting chlorophyll a/b-binding proteins (LHCPs) are the most abundant membrane proteins. LHCP is a nuclear encoded protein which is targeted to the thylakoid membranes by chloroplast signal recognition particles (cpSRP). Insertion into thylakoid membranes is facilitated by the cpSRP receptor cpFtsY and the Alb3 translocase. Work here focused on understanding the molecular events of LHCP insertion into the thylakoid membranes. Specifically, we sought to develop a tool to detect the insertion of the lumen-localized loop of LHCP into thylakoid membranes, which relies on cleavage of the loop by a thylakoid lumen processing protease. We also sought to understand …

Expression Of Lipase From Mycobacterium Tuberculosis In Nicotiana Tobacum And Lactuca Sativa Chloroplasts, Bethany Lloyd

Electronic Theses and Dissertations

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis), is a global threat and the leading cause of death among individuals infected with HIV. TB treatment requires multi-drug cocktails, due to the increasing rates of drug resistance of the bacterium. With multi-drug cocktails, strains have been documented to be resistant to all major drugs in the fight against TB. Since the strains are drug resistant, it calls for an increasing need for vaccine and treatment development for the purpose of preventing and managing the disease. The most widely distributed vaccine against TB is Bacillus Calmette-Gue´rin (BCG). Apart from being …

Amelioration Of Amyloid Burden In Advanced Human And Mouse Alzheimer's Disease Brains By Oral Delivery Of Myelin Basic Protein Bioencapsulated In Plant Cells, Neha Kohli

Electronic Theses and Dissertations

One of the pathological hallmarks of Alzheimer's disease (AD) is the amyloid plaque deposition in aging brains by aggregation of amyloid-β (Aβ) peptides. In this study, the effect of chloroplast derived myelin basic protein (MBP) fused with cholera toxin subunit B (CTB) was investigated in advanced diseased stage of human and mouse AD brains. The CTB-fusion protein in chloroplasts facilitates transmucosal delivery in the gut by the natural binding ability of CTB pentameric form with GM1 receptors on the intestinal epithelium. Further, bioencapsulation of the MBP within plant cells confers protection from enzymes and acids in the digestive system. Here, …

Dynamics Of The Toc Gtpases: Modulation By Nucleotides And Transit Peptides Reveal A Mechanism For Chloroplast Protein Import, Lovett Evan Reddick

Doctoral Dissertations

The chloroplast is the green organelle in the plant cell responsible for harvesting energy from sunlight and converting it into sugars and ATP. Origins of this organelle can be traced back to an endosymbiotic event in which a primitive eukaryotic cell capable of oxidative phosphorylation engulfed a free-living cyanobacterium capable of photosynthetic respiration (1). Immediately following this event the details are not clear, however what is known is that over the course of evolution, the engulfed cyanobacteria relinquished approximately 97% of its protein coding sequences to the host cell nucleus, thus making the newly formed chloroplast reliant on its host …

Determinants For Stop-Transfer And Post-Import Pathways For Protein Targeting To The Chloroplast Inner Envelope Membrane, Antonio A. B. Viana, Ming Li, Danny Schnell

Danny Schnell

he inner envelope membrane (IEM) of the chloroplast plays key roles in controlling metabolite transport between the organelle and cytoplasm and is a major site of lipid and membrane synthesis within the organelle. IEM biogenesis requires the import and integration of nucleus-encoded membrane proteins. Previous reports have led to the conclusion that membrane proteins are inserted into the IEM during protein import from the cytoplasm via a stop-transfer mechanism or are completely imported into the stroma and then inserted into the IEM in a post-import mechanism. In this study, we examined the determinants for each pathway by comparing the targeting …

Phylogenetic Engineering At An Interface Between Large And Small Subunits Imparts Land-Plant Kinetic Properties To Algal Rubisco, Robert J. Spreitzer, Srinivasa R. Peddi, Sriram Satagopan

Department of Biochemistry: Faculty Publications

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the rate-limiting step of photosynthetic CO₂ fixation and, thus, limits agricultural productivity. However, Rubisco enzymes from different species have different catalytic constants. If the structural basis for such differences were known, a rationale could be developed for genetically engineering an improved enzyme. Residues at the bottom of the large-subunit α/β-barrel active site of Rubisco from the green alga Chlamydomonas reinhardtii (methyl-Cys-256, Lys-258, and Ile-265) were previously changed through directed mutagenesis and chloroplast transformation to residues characteristic of land-plant Rubisco (Phe-256, Arg-258, and Val-265). The resultant enzyme has decreases in carboxylation efficiency and CO₂/O …

Elimination Of The Chlamydomonas Gene Family That Encodes The Small Subunit Of Ribulose-1,5-Bisphosphate Carboxylaseyoxygenase, Irina Khrebtukova, Robert J. Spreitzer

Department of Biochemistry: Faculty Publications

Ribulose-1,5-bisphosphate carboxylasey oxygenase (EC 4.1.1.39) is the key photosynthetic enzyme that catalyzes the first step of CO₂ fixation. The chloroplastlocalized holoenzyme of plants and green algae contains eight nuclear-encoded small subunits and eight chloroplastencoded large subunits. Although much has been learned about the enzyme active site that resides within each large subunit, it has been difficult to assess the role of eukaryotic small subunits in holoenzyme function and expression. Small subunits are coded by a family of genes, precluding genetic screening or nuclear transformation approaches for the recovery of small-subunit mutants. In this study, the two small-subunit genes of …