Life Sciences Commons^™

Connections Between Mechanosensitive Ion Channel Msl10 And Er-Plasma Membrane Contact Sites, Jennette Marie Codjoe

Arts & Sciences Electronic Theses and Dissertations

Mechanosensitive (MS) ion channels are an evolutionarily conserved way for cells to sense mechanical forces and transduce them into ionic signals. A plasma membrane-localized MS channel from Arabidopsis thaliana, MscS-Like (MSL)10, senses cell swelling and initiates a signaling cascade that triggers programmed cell death. Whereas the channel properties of MSL10 have been well studied, how MSL10 signals remains largely unknown. I worked collaboratively to show that important lesions for cell death signaling in the cytosolic N- and C-terminal domains of MSL10 interact genetically. I also helped show that ionic flux through MSL10 is dispensable for signaling, which suggested that MSL10 …

Mechanisms For High Light Tolerance In A Fast-Growing Cyanobacterium, Patricia Walker

Arts & Sciences Electronic Theses and Dissertations

Through oxygenic photosynthesis, cyanobacteria, algae, and plants convert light into chemical energy. However, highly energetic light often damages the photosynthetic apparatus, which can lead to the decline of photosynthetic activity (photoinhibition), and prolonged photoinhibition can lead to cell death. Cyanobacteria enact various protective mechanisms to mitigate photodamage, many of which have been conserved in plants. Repair of PSII reaction centers, decreased light absorption, quenching of excess absorbed energy, and biosynthesis of antioxidants all work to mitigate damage during high light. Due to the adjustments to photosynthesis, acclimation to high light requires remodeling of cellular metabolism and physiology. Therefore, phototrophs have …

The Myriad Of Things: Paleoethnobotany Of The Chenopodium Album Aggregate In Northern China, Mana Hayashi Tang

Arts & Sciences Electronic Theses and Dissertations

Carbonized macrobotanical remains of the Chenopodium album aggregate (Amaranthaceae) are highly ubiquitous at archaeological sites. These chenopods are early successional plants and ruderals, which grow well in disturbed ecosystems, including those that they co-habit and co-create with humans. Often distinguished from known agricultural crops (e.g., rice, millet) as a weed, chenopods have received less attention in early food culture studies, despite their ethnohistory as a grain crop, vegetable, and famine food. Their seed remains in northern China exhibit regionally variable morphological attributes, different from those seen in chenopod cultivars of the Americas. Their morphological variability may be a result of …

Assembly And Repair Of Photosystem Ii, Virginia M. Johnson

Arts & Sciences Electronic Theses and Dissertations

Photosystem II is a light-driven water-plastoquinone oxidoreductase present in cyanobacteria, plants, and algae. It is the photosynthetic membrane protein complex responsible for oxidizing water into molecular oxygen, which is necessary for life as we know it. As a multi-subunit membrane-protein-pigment complex, Photosystem II undergoes a complex cycle of assembly, damage, and repair called the Photosystem II lifecycle. This cycle must consistently occur to maintain a high level of photosynthetic activity at the cellular level. Cyanobacteria, oxygenic photosynthetic bacteria, are frequently used as model organisms to study oxygenic photosynthetic processes due to their ease of growth and genetic manipulation. Cyanobacterial PSII …

The Evolutionary History Of Camelina Crantz (Brassicaceae) And Domestication Of The Biofuel Crop, C. Sativa (L.) Crantz, Jordan Brock

Arts & Sciences Electronic Theses and Dissertations

The mustard family, Brassicaceae, is a large and economically important group of plants comprising ~350 genera and ~4060 species. Within the family, one genus, Camelina, has been neglected and nearly forgotten until recent decades. This genus comprises between 7 – 9 species, and includes Camelina sativa, an ancient oilseed crop cultivated for thousands of years in Europe. An allohexaploid, C. sativa contains high levels of omega-3 fatty acids and a seed oil composition amenable for production of aviation jet fuel. With a short generation time and ability to be cultivated on marginal soils with few inputs, C. sativa is set …

The Garden Of Extraterrestrial Deee-Lites, Jessica Bremehr

Graduate School of Art Theses

I present a delusion where you, the reader, are a hitchhiker on a journey toward an alternate realm guided by a god-like buffoon. While I take you on a journey through my daydreams and my musings on an alternate existence, a tour guide will lead the way to an otherworldly realm called The Garden of Extraterrestrial Deee-Lites, reflective of a tourist experience to a faraway destination. The tour will culminate in an uncanny space where curious life forms converge with familiar objects to encourage a sense of wonder while promoting ideas of interconnectedness within the world around us.

The Genetic Basis Of Adaptation To Environmental Stress In Two Grass Genomic Model Systems, David Mitchell Goad

Arts & Sciences Electronic Theses and Dissertations

Plants are exposed to a wide variety of environmental stress in the wild and have developed an equally diverse set of adaptations to tolerate them. The evolutionary processes that have led to this functional diversification, and the specific genes and physiological mechanisms involved, are of immense interest to both evolutionary biologists and crop breeders. In this dissertation I investigate adaptation to different types of environmental stress in two economically important grass species, seashore paspalum (Paspalum vaginatum Sw.) and rice (Oryza sativa L.).

Seashore paspalum is a halophytic turfgrass that occupies habitats which can dramatically differ in salt concentration. Populations may …

Phylogenetic And Genomic Characterization Of The Host-Pathogen Arms Race Between Bacterial Pathogens And Gossypium Hirsutum, Anne Zimmerman Phillips

Arts & Sciences Electronic Theses and Dissertations

Hosts and pathogens are eternally intertwined in an evolutionary arms race. When a pathogen causes a disease outbreak, scientists must identify resistance strategies that can durably tilt the arms race in favor of the host. This requires a deep understanding of both the genetic and environmental contexts in which the outbreak occurs. In this thesis I investigate the bacterial pathogens Xanthomonas citri pv. malvacearum (Xcm) and Pseudomonas syringae that caused disease outbreaks on Gossypium hirsutum from 2011-2017. I use pathogen genomics and host transcriptomics to develop hypotheses for how these pathogens emerged and how they cause disease. Phylogenetics and virulence …

Diverse Far-Red Light Utilization Strategies In Cyanobacteria And Algae, Benjamin Martin Wolf

Arts & Sciences Electronic Theses and Dissertations

In their natural environments, photosynthetic organisms are often exposed to widely varied light environments. Species adapted to shade light, often found growing in lower layers of photosynthetic biofilms, must survive on filtered light alone. Filtered light is highly enriched in far-red wavelengths, which are normally unavailable for photosynthetic energy production in most oxygenic phototrophs. To overcome light limitations in filtered light environments, some species of algae and cyanobacteria utilize specialized photosynthetic pigments and antenna systems to harvest these far-red wavelengths. By sampling the natural environment and using custom-built far-red light growth chambers, I have isolated several species of oxygenic phototrophs …

Plant Metabolic Pathways And Regulatory Networks For Aromatic Amino Acids And Hormones, Cynthia Holland

Arts & Sciences Electronic Theses and Dissertations

Unlike humans and other metazoans, organisms such as fungi, bacteria, and plants have retained the enzymatic machinery necessary to synthesize their aromatic amino acids de novo. Chorismate, the final product of the shikimate pathway, is the precursor to the three aromatic amino acidsѠtryptophan, tyrosine, and phenylalanineѠand is upstream of a number of plant growth hormones, including auxins and benzoates. Phenylalanine and tyrosine both stem from the precursor prephenate, which is formed from chorismate by chorismate mutase, and use dehydrogenases, aminotransferases, and dehydratases in their biosynthetic pathways. Although aromatic amino acid biosynthesis is important for protein synthesis, secondary metabolism, and human …

Nonpolar Residues In The Presumptive Pore‐Lining Helix Of Mechanosensitive Channel Msl10 Influence Channel Behavior And Establish A Nonconducting Function, Grigory Maksaev, Jennette K. Shoots, Simran Ohri, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

Mechanosensitive (MS) ion channels provide a universal mechanism for sensing and responding to increased membrane tension. MscS‐like (MSL) 10 is a relatively well‐studied MS ion channel from Arabidopsis thaliana that is implicated in cell death signaling. The relationship between the amino acid sequence of MSL10 and its conductance, gating tension, and opening and closing kinetics remains unstudied. Here, we identify several nonpolar residues in the presumptive pore‐lining transmembrane helix of MSL10 (TM6) that contribute to these basic channel properties. F553 and I554 are essential for wild type channel conductance and the stability of the open state. G556, a glycine residue …

Kelch F-Box Protein Positively Influences Arabidopsis Seed Germination By Targeting Phytochrome-Interacting Factor1, Manoj Majee, Santosh Kumar, Praveen Kumar Kathare, Shuiqin Wu, Derek Gingerich, Nihar R. Nayak, Louai Salaita, Randy Dinkins, Kathleen Martin, Michael Goodin, Lynnette M A Dirk, Taylor D. Lloyd, Ling Zhu, Joseph Chappell, Arthur G. Hunt, Richard D. Vierstra, Enamul Huq, A Bruce Downie

Biology Faculty Publications & Presentations

Seeds employ sensory systems that assess various environmental cues over time to maximize the successful transition from embryo to seedling. Here we show that the Arabidopsis F-BOX protein COLD TEMPERATURE-GERMINATING (CTG)-10, identified by activation tagging, is a positive regulator of this process. When overexpressed (OE), CTG10 hastens aspects of seed germination. CTG10 is expressed predominantly in the hypocotyl, and the protein is localized to the nucleus. CTG10 interacts with PHYTOCHROME-INTERACTING FACTOR 1 (PIF1) and helps regulate its abundance in planta. CTG10-OE accelerates the loss of PIF1 in light, increasing germination efficiency, while PIF1-OE lines fail to complete germination in …

Proteasome Storage Granules Protect Proteasomes From Autophagic Degradation Upon Carbon Starvation, Richard S. Marshall, Richard D. Vierstra

Biology Faculty Publications & Presentations

26S proteasome abundance is tightly regulated at multiple levels, including the elimination of excess or inactive particles by autophagy. In yeast, this proteaphagy occurs upon nitrogen starvation but not carbon starvation, which instead stimulates the rapid sequestration of proteasomes into cytoplasmic puncta termed proteasome storage granules (PSGs). Here, we show that PSGs help protect proteasomes from autophagic degradation. Both the core protease and regulatory particle sub-complexes are sequestered separately into PSGs via pathways dependent on the accessory proteins Blm10 and Spg5, respectively. Modulating PSG formation, either by perturbing cellular energy status or pH, or by genetically eliminating factors required for …

Roles Of Peroxisomes And Peroxisome-Derived Products In Controlling Plant Growth And Stress Responses, Elizabeth May Frick

Arts & Sciences Electronic Theses and Dissertations

The peroxisome is a vital organelle conserved through the entire eukaryotic lineage. In all examined species, peroxisomes are responsible for such essential processes as fatty acid beta-oxidation and metabolism of reactive oxygen species (ROS). In plants, peroxisomes have taken on additional specialized roles, such as production of some plant hormones and vitamins. In this work, I have uncovered novel factors regulating peroxisome number in model species Arabidopsis thaliana, and novel mechanisms governing how peroxisomes respond to salt stress. I discovered a role for Arabidopsis MAP KINASE17 (MPK17) as a negative regulator of peroxisome division that acts in the salt-stress response …

Analysis Of Argonaute-Small Rna-Transcription Factor Circuits Controlling Leaf Development, John Steen Hoyer

Arts & Sciences Electronic Theses and Dissertations

Experimental studies of plant development have yielded many insights into gene regulation, revealing interactions between core transcriptional and post-transcriptional regulatory pathways present in all land plants. This work describes a direct connection between the three main small RNA-transcription factor circuits controlling leaf shape dynamics in the reference plant Arabidopsis thaliana. We used a high-throughput yeast 1-hybrid platform to identify factors directly binding the promoter of the highly specialized ARGONAUTE7 silencing factor. Two groups of developmentally significant microRNA-targeted transcription factors were the clearest hits from these screens, but transgenic complementation analysis indicated that their binding sites make only a small contribution …

Phyllotactic Regularity Requires The Paf1 Complex In Arabidopsis, Kateryna Fal, Mengying Liu, Assem Duisembekova, Yassin Refahi, Elizabeth S. Haswell, Olivier Hamant

Biology Faculty Publications & Presentations

In plants, aerial organs are initiated at stereotyped intervals, both spatially (every 137° in a pattern called phyllotaxis) and temporally (at prescribed time intervals called plastochrons). To investigate the molecular basis of such regularity, mutants with altered architecture have been isolated. However, most of them only exhibit plastochron defects and/or produce a new, albeit equally reproducible, phyllotactic pattern. This leaves open the question of a molecular control of phyllotaxis regularity. Here, we show that phyllotaxis regularity depends on the function of VIP proteins, components of the RNA polymerase II-associated factor 1 complex (Paf1c). Divergence angles between successive organs along the …

Photosensing And Thermosensing By Phytochrome B Require Both Proximal And Distal Allosteric Features Within The Dimeric Photoreceptor, E Sethe Burgie, Adam N. Bussell, Shu-Hui Lye, Tong Wang, Weiming Hu, Katrice E. Mcloughlin, Erin L. Weber, Huilin Li, Richard D. Vierstra

Biology Faculty Publications & Presentations

Phytochromes (Phys) encompass a diverse collection of bilin-containing photoreceptors that help plants and microorganisms perceive light through photointerconversion between red light (Pr) and far-red light (Pfr)-absorbing states. In addition, Pfr reverts thermally back to Pr via a highly enthalpic process that enables temperature sensation in plants and possibly other organisms. Through domain analysis of the Arabidopsis PhyB isoform assembled recombinantly, coupled with measurements of solution size, photoconversion, and thermal reversion, we identified both proximal and distal features that influence all three metrics. Included are the downstream C-terminal histidine kinase-related domain known to promote dimerization and a conserved patch just upstream …

Plant Mechanosensitive Ion Channels: An Ocean Of Possibilities, Debarati Basu, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

Mechanosensitive ion channels, transmembrane proteins that directly couple mechanical stimuli to ion flux, serve to sense and respond to changes in membrane tension in all branches of life. In plants, mechanosensitive channels have been implicated in the perception of important mechanical stimuli such as osmotic pressure, touch, gravity, and pathogenic invasion. Indeed, three established families of plant mechanosensitive ion channels play roles in cell and organelle osmoregulation and root mechanosensing - and it is likely that many other channels and functions await discovery. Inspired by recent discoveries in bacterial and animal systems, we are beginning to establish the conserved and …

Life Behind The Wall: Sensing Mechanical Cues In Plants, Olivier Hamant, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

There is increasing evidence that all cells sense mechanical forces in order to perform their functions. In animals, mechanotransduction has been studied during the establishment of cell polarity, fate, and division in single cells, and increasingly is studied in the context of a multicellular tissue. What about plant systems? Our goal in this review is to summarize what is known about the perception of mechanical cues in plants, and to provide a brief comparison with animals.

Seeds As Artifacts Of Communities Of Practice: The Domestication Of Erect Knotweed In Eastern North America, Natalie Graham Mueller

Arts & Sciences Electronic Theses and Dissertations

Humans are the ultimate ecosystem engineers, and in transforming ecosystems we also change the selective environment for the plants and animals that live among us. The bodies and behaviors of domesticated plants and animals are thus rich artifacts of traditional ecological knowledge and practice. I study the morphology and behavior of domesticated plants as a proxy for ancient agricultural communities of practice. The transition from food procurement to food production is one of the most significant shifts in human history. I consider this process as the evolution and spread of a knowledge system. Domestication studies are usually focused on differentiating …

The Arabidopsis Kinesin-4, Fra1, Requires A High Level Of Processive Motility To Function Correctly, Anindya Ganguly, Logan Demott, Ram Dixit

Biology Faculty Publications & Presentations

Processivity is important for kinesins that mediate intracellular transport. Structure–function analyses of N-terminal kinesins (i.e. kinesins comprising their motor domains at the N-terminus) have identified several non-motor regions that affect processivity in vitro. However, whether these structural elements affect kinesin processivity and function in vivo is not known. Here, we used an Arabidopsis thaliana kinesin-4, called Fragile Fiber 1 (FRA1, also known as KIN4A), which is thought to mediate vesicle transport, to test whether mutations that alter processivity in vitro lead to similar changes in behavior in vivo and whether processivity is important for the function of FRA1. We …

The Rna Polymerase-Associated Factor 1 Complex Is Required For Plant Touch Responses, Gregory S. Jensen, Kateryna Fal, Olivier Hamant, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

Thigmomorphogenesis is a stereotypical developmental alteration in the plant body plan that can be induced by repeatedly touching plant organs. To unravel how plants sense and record multiple touch stimuli we performed a novel forward genetic screen based on the development of a shorter stem in response to repetitive touch. The touch insensitive (ths1) mutant identified in this screen is defective in some aspects of shoot and root thigmomorphogenesis. The ths1 mutant is an intermediate loss-of-function allele of VERNALIZATION INDEPENDENCE 3 (VIP3), a previously characterized gene whose product is part of the RNA polymerase II-associated factor 1 …

Phytochrome B Integrates Light And Temperature Signals In Arabidopsis, Martina Legris, Cornelia Klose, E Sethe Burgie, Cecilia Costigliolo Rojas Rojas, Maximiliano Neme, Andreas Hiltbrunner, Philip A. Wigge, Eberhard Schäfer, Richard D. Vierstra, Jorge J. Casal

Biology Faculty Publications & Presentations

Ambient temperature regulates many aspects of plant growth and development, but its sensors are unknown. Here, we demonstrate that the phytochrome B (phyB) photoreceptor participates in temperature perception through its temperature-dependent reversion from the active Pfr state to the inactive Pr state. Increased rates of thermal reversion upon exposing Arabidopsis seedlings to warm environments reduce both the abundance of the biologically active Pfr-Pfr dimer pool of phyB and the size of the associated nuclear bodies, even in daylight. Mathematical analysis of stem growth for seedlings expressing wild-type phyB or thermally stable variants under various combinations of light and temperature revealed …

Msl1 Is A Mechanosensitive Ion Channel That Dissipates Mitochondrial Membrane Potential And Maintains Redox Homeostasis In Mitochondria During Abiotic Stress, Chun Pong Lee, Grigory Maksaev, Gregory S. Jensen, Monika W. Murcha, Margaret E. Wilson, Mark Fricker, Ruediger Hell, Elizabeth S. Haswell, A Harvey Millar, Lee J. Sweetlove

Biology Faculty Publications & Presentations

Mitochondria must maintain tight control over the electrochemical gradient across their inner membrane to allow ATP synthesis while maintaining a redox-balanced electron transport chain and avoiding excessive reactive oxygen species production. However, there is a scarcity of knowledge about the ion transporters in the inner mitochondrial membrane that contribute to control of membrane potential. We show that loss of MSL1, a member of a family of mechanosensitive ion channels related to the bacterial channel MscS, leads to increased membrane potential of Arabidopsis mitochondria under specific bioenergetic states. We demonstrate that MSL1 localises to the inner mitochondrial membrane. When expressed in …

Purification Of 26s Proteasomes And Their Subcomplexes From Plants, Richard S. Marshall, David C. Gemperline, Richard D. Vierstra

Biology Faculty Publications & Presentations

The 26S proteasome is a highly dynamic, multisubunit, ATP-dependent protease that plays a central role in cellular housekeeping and many aspects of plant growth and development by degrading aberrant polypeptides and key cellular regulators that are first modified by ubiquitin. Although the 26S proteasome was originally enriched from plants over 30 years ago, only recently have significant advances been made in our ability to isolate and study the plant particle. Here, we describe two robust methods for purifying the 26S proteasome and its subcomplexes from Arabidopsis thaliana; one that involves conventional chromatography techniques to isolate the complex from wild-type …

Plastid Osmotic Stress Influences Cell Differentiation At The Plant Shoot Apex, Margaret E. Wilson, Matthew Mixdorf, R Howard Berg, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

The balance between proliferation and differentiation in the plant shoot apical meristem is controlled by regulatory loops involving the phytohormone cytokinin and stem cell identity genes. Concurrently, cellular differentiation in the developing shoot is coordinated with the environmental and developmental status of plastids within those cells. Here, we employ an Arabidopsis thaliana mutant exhibiting constitutive plastid osmotic stress to investigate the molecular and genetic pathways connecting plastid osmotic stress with cell differentiation at the shoot apex. msl2 msl3 mutants exhibit dramatically enlarged and deformed plastids in the shoot apical meristem, and develop a mass of callus tissue at the shoot …

Rna Sequencing Analysis Of The Msl2msl3, Crl, And Ggps1 Mutants Indicates That Diverse Sources Of Plastid Dysfunction Do Not Alter Leaf Morphology Through A Common Signaling Pathway, Darron R. Luesse, Margaret E. Wilson, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

Determining whether individual genes function in the same or in different pathways is an important aspect of genetic analysis. As an alternative to the construction of higher-order mutants, we used contemporary expression profiling methods to perform pathway analysis on several Arabidopsis thaliana mutants, including the mscS-like (msl)2msl3 double mutant. MSL2 and MSL3 are implicated in plastid ion homeostasis, and msl2msl3 double mutants exhibit leaves with a lobed periphery, a rumpled surface, and disturbed mesophyll cell organization. Similar developmental phenotypes are also observed in other mutants with defects in a range of other chloroplast or mitochondrial functions, including …

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.

Stochastic Models For Plant Microtubule Self-Organization And Structure, Ezgi Can Eren, Ram Dixit, Natarajan Gautam

Biology Faculty Publications & Presentations

One of the key enablers of shape and growth in plant cells is the cortical microtubule (CMT) system, which is a polymer array that forms an appropriately-structured scaffolding in each cell. Plant biologists have shown that stochastic dynamics and simple rules of interactions between CMTs can lead to a coaligned CMT array structure. However, the mechanisms and conditions that cause CMT arrays to become organized are not well understood. It is prohibitively time-consuming to use actual plants to study the effect of various genetic mutations and environmental conditions on CMT self-organization. In fact, even computer simulations with multiple replications are …

Mechanosensitive Channel Msl8 Regulates Osmotic Forces During Pollen Hydration And Germination, Eric S. Hamilton, Gregory S. Jensen, Grigory Maksaev, Andrew Katims, Ashley M. Sherp, Elizabeth S. Haswell

Biology Faculty Publications & Presentations

Pollen grains undergo dramatic changes in cellular water potential as they deliver the male germ line to female gametes, and it has been proposed that mechanosensitive ion channels may sense the resulting mechanical stress. Here, we identify and characterize MscS-like 8 (MSL8), a pollen-specific, membrane tension–gated ion channel required for pollen to survive the hypoosmotic shock of rehydration and for full male fertility. MSL8 negatively regulates pollen germination but is required for cellular integrity during germination and tube growth. MSL8 thus senses and responds to changes in membrane tension associated with pollen hydration and germination. These data further suggest that …