Mechanisms and Consequences of Microtubule-Based Symmetry Breaking in Plant Roots

Directional growth in plants is primarily determined by the axis of cell expansion, which is specified by the net orientation of cortical microtubules. Microtubules guide the deposition of cellulose and other cell wall materials. In rapidly elongating cells, transversely oriented microtubules create material anisotropy in the cell wall that prevents radial cell expansion, channeling cell expansion in the longitudinal direction. Mutations perturbing microtubule organization frequently lead to aberrant cell growth in land plants, with some mutations leading to helical growth patterns (called ‘twisted mutants’), often in roots. This phenotype manifests as right-handed or left-handed twisting of cell files along the long axis of plant organs, which correlates with rightward or leftward organ growth, respectively. Helical growth is a common occurrence in the plant kingdom and serves a variety of purposes, but the molecular mechanisms that produce helical growth and define handedness are not well understood. Furthermore, how molecular-level processes propagate across spatial scales to control organ-level growth is undefined. Here, I used the model plant Arabidopsis thaliana as an experimentally tractable system, focusing on the root organ to study the mechanisms underlying helical growth in plants. In this work, I used roots as a model plant organ to investigate the molecular mechanisms that control symmetry maintenance and symmetry breaking in plants. Arabidopsis roots are ideally suited for this work because of their simple, concentric ring-like cellular anatomy and well-defined process of development. I selected two Arabidopsis twisted mutants with opposite chirality to study whether the emergence of right-handed and left-handed helical growth involves conserved or distinct mechanisms. Cortical microtubules are skewed in the right-handed spr1 mutant, which lacks a microtubule plus end-associated protein that regulates polymerization dynamics. In contrast, cortical microtubules tend to be laterally displaced in the left-handed cmu1 mutant, which lacks a protein that contributes to the attachment of cortical microtubules to the plasma membrane. Using a cell-type specific complementation approach, I showed that both SPR1 and CMU1 gene expression in the epidermis alone is sufficient to maintain wild-type-like straight cell files and root growth. In addition, epidermal expression of SPR1 restores both the morphology and skew of the cortical cell file to wild-type-like. By genetically disrupting cell-cell adhesion in the spr1 mutant, I found that a physical connection between epidermal and cortical cells is required for the epidermis to cause organ-level skewed growth. Together, these data demonstrate that the epidermis plays a central role in maintaining straight root growth, suggesting that twisted plant growth in nature could arise by altering microtubule behavior in the epidermis alone and does not require null alleles in all cells. To examine whether cortical microtubule defects in the spr1-3 mutant affect cell growth, I conducted morphometry analysis. I found that while skewed cortical microtubule orientation correlates with asymmetric epidermal cell morphology and growth in the spr1-3 mutant root meristem, cell file twisting is not manifested until the differentiation zone of the root where cell growth slows down and root hairs emerge. Furthermore, I demonstrated that cell file twisting is not sufficient to generate skewed growth at the organ level, which requires that the root is grown on an agar medium, a mechanically heterogeneous environment. Increasing the stiffness of the agar medium caused the spr1-3 and cmu1 mutant roots to grow straight, indicating that mechanical stimuli influence twisted root growth. Despite their important role in root anchorage, root hairs on the epidermis are not required for skewed root growth, nor for reorienting root skewing in response to changes in the mechanical environment. Overall, this work provides new insights into how symmetry breaking affects root mechanoresponse. Spatial heterogeneity in the composition and organization of the plant cell wall affects its mechanics to control cell shape and directional growth. In the last chapter of this work, I describe a new methodology for imaging plant primary cell walls at the nanoscale using atomic force microscopy coupled with infrared spectroscopy (AFM-IR). I contributed to generating a novel sample preparation technique and employed AFM-IR and spectral deconvolution to generate high-resolution spatial maps of the mechanochemical signatures of the Arabidopsis epidermal cell wall. Cross-correlation analysis of the spatial distribution of chemical and mechanical properties suggested that the carbohydrate composition of cell wall junctions correlates with increased local stiffness. In developing this methodology, this chapter provides an essential foundation for applying AFM-IR to understand the complex mechanochemistry of intact plant cell walls at nanometer resolution

Participatory Development of a Forage Grass Cultivar

Perennial forage grasses exist in both nature and agriculture as a highly heterogeneous mixture of genotypes. Extreme environments, fluctuating environments, and severe managements can impose selection pressures that will result in loss of unadapted genotypes. Mortality of unadapted genotypes leads to dominance of fewer highly adapted genotypes which may be useful as superior germplasm in other similar environments

Educational and Environmental Support for Novice E‐Learning Developers

The e‐learning marketplace is evolving. Many organizations use rapid e‐learning development tools today, and instructional designers often need to upgrade their marketable skill‐sets as applied to e‐learning. We gathered survey and interview data from academic and corporate samples of instructional designers and e‐learning developers to investigate which features of rapid e‐learning development tools they value and why. Results suggest that formal education and organizational support are needed to help them become competent and marketable e‐learning practitioners

The evolution of public health genomics: Exploring its past, present, and future

Public health genomics has evolved to responsibly integrate advancements in genomics into the fields of personalized medicine and public health. Appropriate, effective and sustainable integration of genomics into healthcare requires an organized approach. This paper outlines the history that led to the emergence of public health genomics as a distinguishable field. In addition, a range of activities are described that illustrate how genomics can be incorporated into public health practice. Finally, it presents the evolution of public health genomics into the new era of “precision public health.

Розподіл вмісту важких металів у системі «вода – донні відкладення» транскордонної річки Уж

The dynamics and peculiarities of the heavy metals (Cu, Pb, Zn, As, V, Cr, Ni) migration were established in the system of the river Uzh bottom deposits. An excess in maximum permissible concentration among such elements as Zn, V, As, and Cu was detected in surface waters. We may connect the elevated level of Cu and Zn with natural (metals appearing in ground water run-off, ablation from iron ore, the reaction of interstitial water), anthropogenic (sewage disposals from communal households and manufacturing plants, agricultural run-offs), and hydrochemical (pH of water medium, methylation of non-organic metal compounds, metals release from the organic compounds composition, ingress from bottom deposits) factors. The high concentrations of vanadium in water as well as in bottom deposits are most probably induced by the leaching of elements from the regional volcanic rocks. The plumbum content did not exceed the higher-than-normal rates; however, significant element accumulation was detected in bottom deposits outside the city of Uzhgorod which may be the result of ecotoxicant ingress along with land runoff from the riverside highways laid parallel to the water course. In comparison with background measures, the highest chromium and nickel concentrations were detected near the streamlet Domoradzh and, therefore, it is assumed that the industrial wastewaters serve here as a source of heavy metals. The reservoir in the lowland is above all enriched by arsenic. Areas under agricultural use are significantly concentrated in lowlands. Runoffs from these areas are the main source of the ore supply. However, the impact of municipal domestic waste water which contains arsenic-containing detergents should not be excluded. Moreover, we found a relationship between the relief heterogeneity of the study area and distribution of heavy metals in the hydro-ecosystem. The accomplished comparative analysis of the territories under study indicates the significant pollution level of the surface waters in technologically transformed areas, whereas the largest accumulation of pollutants is concentrated in bottom deposits of the river, which indicates a constant supply of pollutants to the streamflow. Встановлено динаміку та особливості міграції важких металів (Cu, Pb, Zn, As, V, Cr, Ni) у системі «вода – донні відклади» річки Уж. У поверхневих водах зафіксовано перевищення ГДК для таких елементів, як Zn, V, As та Cu. Підвищений вміст купруму та цинку пов’язуємо з природнbми (вимивання з гірських порід, реакція ґрунтового розчину), антропогенними (стічні води комунально-побутових господарств, промислових підприємств, сільськогосподарські стоки) та гідрохімічними (рН водного середовища, вивільнення металів зі складу органічних сполук, їх надходження з донних відкладів) факторами. Високі концентрації ванадію як у воді, так і в донних відкладах найімовірніше спричинені вимиванням елемента з вулканічних гірських порід, поширениху даній області. Вміст плюмбуму не перевищував наднормативних значень, однак виявлена значна акумуляція елементу в донних відкладах за межами міста Ужгород, що може бути наслідком надходження екотоксиканта з поверхневим стоком із прибережних автосмуг, прокладених паралельно водотоку. Порівняно з фоновими показниками найвищі концентрації хрому та нікелю зафіксовано неподалік від струмка Доморадж, тому припускаємо, що джерелом важких металів тут виступають промислові стічні води. Арсеном найбільш збагачена водойма в пониззі, де зосереджено чимало сільськогосподарських угідь, змиви з яких – основне джерело надходження металу. Здійснено порівняльний аналіз досліджуваних територій, який указує на значний рівень забруднення поверхневих вод у районі техногенно трансформованої території, тоді як найбільша акумуляція полютантів зосереджена в донних відкладах пониззя річки, що свідчить про регулярне надходження забруднюючих речовин до водотоку.

Aberrant phase precession of lateral septal cells in a maternal immune activation model of schizophrenia risk may disrupt the integration of location with reward

Spatial memory and reward processing are known to be disrupted in schizophrenia. Since the lateral septum (LS) may play an important role in the integration of location and reward, we examined the effect of maternal immune activation (MIA), a known schizophrenia risk factor, on spatial representation in the rat LS. In support of a previous study, we found that spatial location is represented as a phase code in the rostral LS of adult male rats, so that LS cell spiking shifts systematically against the phase of the hippocampal, theta-frequency, local field potential (LFP) as an animal moves along a track towards a reward (phase precession). Whereas shallow precession slopes were observed in control (CTL) group cells, they were steeper in the MIA animals, such that firing frequently precessed across several theta cycles as the animal moved along the length of the apparatus, with subsequent ambiguity in the phase representation of location. Furthermore, an analysis of the phase trajectories of the CTL group cells revealed that the population tended to converge towards a common firing phase as the animal approached the reward location. This suggested that phase coding in these cells might signal both reward location and the distance to reward. By comparison the degree of phase convergence in the MIA-group cells was weak, and the region of peak convergence was distal to the reward location. These findings suggest that a schizophrenia risk factor disrupts the phase-based encoding of location-reward relationships in the LS, potentially smearing reward representations across space

Healthcare system priorities for successful integration of genomics: An Australian focus

This paper examines key considerations for the successful integration of genomic technologies into healthcare systems. All healthcare systems strive to introduce new technologies that are effective and affordable, but genomics offers particular challenges, given the rapid evolution of the technology. In this context we frame internationally relevant discussion points relating to effective and sustainable implementation of genomic testing within the strategic priority areas of the recently endorsed Australian National Health Genomics Policy Framework. The priority areas are services, data, workforce, finances, and person-centred care. In addition, we outline recommendations from a government perspective through the lens of the Australian health system, and argue that resources should be allocated not to just genomic testing alone, but across the five strategic priority areas for full effectiveness

Hippocampal sequencing mechanisms are disrupted in a maternal immune activation model of schizophrenia risk

Episodic memory requires information to be stored and recalled in sequential order, and these processes are disrupted in schizophrenia. Hippocampal phase precession and theta sequences are thought to provide a biological mechanism for sequential ordering of experience at timescales suitable for plasticity. These phenomena have not previously been examined in any models of schizophrenia risk. Here, we examine these phenomena in a maternal immune activation (MIA) rodent model. We show that while individual pyramidal cells in the CA1 region continue to precess normally in MIA animals, the starting phase of precession as an animal enters a new place field is considerably more variable in MIA animals than in controls. A critical consequence of this change is a disorganization of the ordered representation of experience via theta sequences. These results provide the first evidence of a biological-level mechanism that, if it occurs in schizophrenia, may explain aspects of disorganized sequential processing that contribute to the cognitive symptoms of the disorder