PIN Polarity Research Articles

Room‐Temperature Ferromagnetism and Fermi Level Pinning in Multilayer Graphene Films Derived from Ferrocene

AbstractSpin polarization is a very important condition for spintronics applications which can easily be achieved by using ferromagnetic materials. Graphene‐based magnetic materials, which have long spin lifetime and diffusion length, are very promising as spin channel materials. In this work, Ferrocene molecules are chosen as the precursor carbon source using the chemical vapor deposition method, facilitating the synthesis of multilayer graphene films decorated with magnetic nanoclusters. This resultant material manifested planar ferromagnetism with a Curie temperature exceeding room temperature (≥300 K) and a saturation magnetization as high as 4.1 × 10−7 emu mm−2. The robust ferromagnetic coupling can plausibly be attributed to the presence of magnetic nanoclusters interspersed within the synthesized graphene, enhancing the localized magnetic moment and promoting ferromagnetic long‐range ordering. Furthermore, the Fermi level pinning at the Dirac point is observed and predominantly ascribed to the pervasive defects in the graphene derived from ferrocene. The oxygen functional groups within these defects act as charge traps, effectively anchoring the Fermi level to the Dirac point, intrinsically suppressing the ambipolar behavior of graphene. This work sheds light on potential avenues for the exploration of novel, high‐performance carbonaceous spintronics materials with economic feasibility.

The Opportunity of Negative Capacitance Behavior in Flash Memory for High‐Density and Energy‐Efficient In‐Memory Computing Applications

AbstractFlash memory is a promising candidate for use in in‐memory computing (IMC) owing to its multistate operations, high on/off ratio, non‐volatility, and the maturity of device technologies. However, its high operation voltage, slow operation speed, and string array structure severely degrade the energy efficiency of IMC. To address these challenges, a novel negative capacitance‐flash (NC‐flash) memory‐based IMC architecture is proposed. To stabilize and utilize the negative capacitance (NC) effect, a HfO2‐based reversible single‐domain ferroelectric (RSFE) layer is developed by coupling the flexoelectric and surface effects, which generates a large internal field and surface polarization pinning. Furthermore, NC‐flash memory is demonstrated for the first time by introducing a RSFE and dielectric heterostructure layer in which the NC effect is stabilized as a blocking layer. Consequently, an energy‐efficient and high‐throughput IMC is successfully demonstrated using an AND flash‐like cell arrangement and source‐follower/charge‐sharing vector‐matrix multiplication operation on a high‐performance NC‐flash memory.

GhROP6 GTPase modulates auxin accumulation in cotton fibers by regulating cell-specific GhPIN3a localization.

PIN-FORMED- (PIN) mediated polar auxin transport plays a predominant role in most auxin-triggered organogenesis in plants. Global control of PIN polarity at the plasma membrane contributes to the essential establishment of auxin maxima in most multicellular tissues. However, establishment of auxin maxima in single cells is poorly understood. Cotton fibers, derived from ovule epidermal cells by auxin-triggered cell protrusion, provide an ideal model to explore the underlying mechanism. Here, we report that cell-specific degradation of GhPIN3a, which guides the establishment of the auxin gradient in cotton ovule epidermal cells, is associated with the preferential expression of GhROP6 GTPase in fiber cells. In turn, GhROP6 reduces GhPIN3a abundance at the plasma membrane and facilitates intracellular proteolysis of GhPIN3a. Overexpression and activation of GhROP6 promote cell elongation, resulting in a substantial improvement in cotton fiber length.

From the archives: Calcium signaling and PIN polarity, functional divergence after genome duplication, and a 5' inhibitor of gene expression.

From the archives: Calcium signaling and PIN polarity, functional divergence after genome duplication, and a 5' inhibitor of gene expression.

(Digital Presentation) CeOx Capping for Ferroelectric Y:HfO2 Films

In recent years, HfO2 has been paid a lot of attention as a ferroelectric material due to its excellent scalability and complementary-metal-oxide-semiconductor (CMOS) process compatibility [1]. Some of the issues of ferroelectric HfO2 are wake-up and fatigue effect, increase and decrease of remanent polarization (P r) along with switching cycles, and low endurance. Generally, these phenomena are understood as a result of the increase and redistribution of oxygen vacancies (VO) in HfO2 films [2]. By the way, it is reported that CeOx can release and absorb oxygen from adjacent oxides [3]. In this study, we propose the stacking structure of CeOx and ferroelectric HfO2 to improve endurance and investigate electric properties and voltage application sequence to suppress the fatigue effect.5 mol% Y-doped HfO2 (Y:HfO2) and CeOx capping layers of metal-ferroelectric-metal (MFM) capacitors were deposited by atomic-layer-deposition (ALD) with W bottom and top electrodes by sputtering. Post metallization annealing (PMA) was performed at 450 and 500oC for the various duration. Figure 1 shows hysteresis loops of the capacitors with and without CeOx capping annealed at 450oC for 20 minutes. Large hysteresis on CeOx capping is observed even same annealing temperature and duration. Enhancement of transformation to ferroelectric phase can be explained as tensile stress to Y:HfO2 due to the difference of coefficient of thermal expansion (CTE) between CeOx and Y:HfO2. Variation of switching polarization (P SW), the difference between positive and negative P r, as a function of the number of switching cycles is also investigated and shown in figure 2. Both capacitors are annealed at 500oC for 100 minutes to crystallize. In the case of without CeOx capping, continuous wake-up effect and breakdown over 3×107 times switching are observed. On the other hand, the capacitor with CeOx capping shows a slight wake-up effect and fatigue after 106 times switching, additionally, endurance is improved to 3×109 times switching. The reason why fatigue and prolonging endurance occur is suspected that oxygen ions in the CeOx layer pin polarization domains and compensate VO in Y:HfO2. To suppress fatigue, we propose the recovery process by positive DC voltage application to top electrodes. In figure 3, hysteresis loops of the capacitor with CeOx capping before and after recovery voltage application. One can observe the larger hysteresis after recovery.This work was supported by JST-COI (JPMJCE1309). One of the authors, Kazuto Mizutani, was supported by The FUTABA Foundation.[1] T. S. Boscke, et al., Appl. Phys. Lett., 99, 102903 (2011). [2] M. Pesic, et al., Adv. Funct. Mater., 26, pp. 4601–4612 (2016). [3] M. Mamatrishat, et al., Vacuum, 86, pp. 1513-1513 (2012). Figure 1

Constitutive Active CPK30 Interferes With Root Growth and Endomembrane Trafficking in Arabidopsis thaliana.

Calcium-dependent protein kinases (CPK) are key components of a wide array of signaling pathways, translating stress and nutrient signaling into the modulation of cellular processes such as ion transport and transcription. However, not much is known about CPKs in endomembrane trafficking. Here, we screened for CPKs that impact on root growth and gravitropism, by overexpressing constitutively active forms of CPKs under the control of an inducible promoter in Arabidopsis thaliana. We found that inducible overexpression of an constitutive active CPK30 (CA-CPK30) resulted in a loss of root gravitropism and ectopic auxin accumulation in the root tip. Immunolocalization revealed that CA-CPK30 roots have reduced PIN protein levels, PIN1 polarity defects and impaired Brefeldin A (BFA)-sensitive trafficking. Moreover, FM4-64 uptake was reduced, indicative of a defect in endocytosis. The effects on BFA-sensitive trafficking were not specific to PINs, as BFA could not induce aggregation of ARF1- and CHC-labeled endosomes in CA-CPK30. Interestingly, the interference with BFA-body formation, could be reverted by increasing the extracellular pH, indicating a pH-dependence of this CA-CPK30 effect. Altogether, our data reveal an important role for CPK30 in root growth regulation and endomembrane trafficking in Arabidopsis thaliana.

Stochastic Single-Shot Polarization Pinning of Polariton Condensate at High Temperatures.

We resolve single-shot polariton condensate polarization dynamics, revealing a high degree of circular polarization persistent up to T=170 K. The statistical analysis of pulse-to-pulse polariton condensate polarization elucidates the stochastic nature of the polarization pinning process, which is strongly dependent on the pump laser intensity and polarization. Our experiments show that by spatial trapping and isolating condensates from their noisy environment it is possible to form strongly spin-polarized polariton condensates at high temperatures, offering a promising route to the realization of polariton spin lattices for quantum simulations.

Mechanical buckling can pattern the light-diffracting cuticle of Hibiscus trionum.

Many species have cuticular striations that play a range of roles, from pollinator attraction to surface wettability. In Hibiscus trionum, the striations span multiple cells at the base of the petal to form a pattern that produces a type of iridescence. It is postulated, using theoretical models, that the pattern of striations could result from mechanical instabilities. By combining the application of mechanical stress with high-resolution imaging, we demonstrate that the cuticle buckles to create a striated pattern. Through mechanical modeling and cryo-SEM fractures, we show that the cuticle behaves like a bilayer system with a stiff film on a compliant substrate. The pattern of buckling aligns with the direction of the stress to create a larger-scale pattern. Our findings contribute to the understanding of the formation of tissue-wide patterns in living organisms.

PIN-mediated polar auxin transport regulations in plant tropic responses.

Tropisms, growth responses to environmental stimuli such as light or gravity, are spectacular examples of adaptive plant development. The plant hormone auxin serves as a major coordinative signal. The PIN auxin exporters, through their dynamic polar subcellular localizations, redirect auxin fluxes in response to environmental stimuli and the resulting auxin gradients across organs underlie differential cell elongation and bending. In this review, we discuss recent advances concerning regulations of PIN polarity during tropisms, focusing on PIN phosphorylation and trafficking. We also cover how environmental cues regulate PIN actions during tropisms, as well as the crucial role of auxin feedback on PIN polarity during bending termination. Finally, the interactions between different tropisms are reviewed to understand plant adaptive growth in the natural environment.

Conserved, divergent and heterochronic gene expression during Brachypodium and Arabidopsis embryo development

Key messageDevelopmental and transcriptomic analysis of Brachypodium embryogenesis and comparison with Arabidopsis identifies conserved and divergent phases of embryogenesis and reveals widespread heterochrony of developmental gene expression.Embryogenesis, transforming the zygote into the mature embryo, represents a fundamental process for all flowering plants. Current knowledge of cell specification and differentiation during plant embryogenesis is largely based on studies of the dicot model plant Arabidopsis thaliana. However, the major crops are monocots and the transcriptional programs associated with the differentiation processes during embryogenesis in this clade were largely unknown. Here, we combined analysis of cell division patterns with development of a temporal transcriptomic resource during embryogenesis of the monocot model plant Brachypodium distachyon. We found that early divisions of the Brachypodium embryo were highly regular, while later stages were marked by less stereotypic patterns. Comparative transcriptomic analysis between Brachypodium and Arabidopsis revealed that early and late embryogenesis shared a common transcriptional program, whereas mid-embryogenesis was divergent between species. Analysis of orthology groups revealed widespread heterochronic expression of potential developmental regulators between the species. Interestingly, Brachypodium genes tend to be expressed at earlier stages than Arabidopsis counterparts, which suggests that embryo patterning may occur early during Brachypodium embryogenesis. Detailed investigation of auxin-related genes shows that the capacity to synthesize, transport and respond to auxin is established early in the embryo. However, while early PIN1 polarity could be confirmed, it is unclear if an active response is mounted. This study presents a resource for studying Brachypodium and grass embryogenesis and shows that divergent angiosperms share a conserved genetic program that is marked by heterochronic gene expression.

AGC kinases and MAB4/MEL proteins maintain PIN polarity by limiting lateral diffusion in plant cells

SummaryPolar subcellular localization of the PIN exporters of the phytohormone auxin is a key determinant of directional, intercellular auxin transport and thus a central topic of both plant cell and developmental biology. Arabidopsis mutants lacking PID, a kinase that phosphorylates PINs, or the MAB4/MEL proteins of unknown molecular function display PIN polarity defects and phenocopy pin mutants, but mechanistic insights into how these factors convey PIN polarity are missing. Here, by combining protein biochemistry with quantitative live-cell imaging, we demonstrate that PINs, MAB4/MELs, and AGC kinases interact in the same complex at the plasma membrane. MAB4/MELs are recruited to the plasma membrane by the PINs and in concert with the AGC kinases maintain PIN polarity through limiting lateral diffusion-based escape of PINs from the polar domain. The PIN-MAB4/MEL-PID protein complex has self-reinforcing properties thanks to positive feedback between AGC kinase-mediated PIN phosphorylation and MAB4/MEL recruitment. We thus uncover the molecular mechanism by which AGC kinases and MAB4/MEL proteins regulate PIN localization and plant development.

Optical orientation, polarization pinning, and depolarization dynamics in optically confined polariton condensates

We investigate the optical orientation, polarization pinning, and depolarization of optically confined semiconductor exciton-polariton condensates. We perform a complete mapping of the condensate polarization as a function of incident nonresonant excitation polarization and power. We utilize a ring-shaped excitation pattern to generate an exciton-induced potential that spatially confines polariton condensates into a single mode. We observe that formation of circular polarization in the condensate persists even for a weakly cocircularly polarized pump. By varying the excitation ring diameter we realize a transition from the condensate polarization being pinned along the coordinate-dependent cavity-strain axes, to a regime of zero degree of condensate polarization. Analysis through the driven-dissipative stochastic Gross-Pitaevskii equation reveals that this depolarization stems from a competition between sample induced in-plane polarization splitting and the condensate-reservoir overlap. An increase in the role of the latter results in weakening of the condensate fixed-point phase space attractors, and enhanced random phase space walk and appearance of limit cycle trajectories, reducing the degree of time-integrated polarization.

Arabidopsis Flippases Cooperate with ARF GTPase Exchange Factors to Regulate the Trafficking and Polarity of PIN Auxin Transporters.

Cell polarity is a fundamental feature of all multicellular organisms. PIN auxin transporters are important cell polarity markers that play crucial roles in a plethora of developmental processes in plants. Here, to identify components involved in cell polarity establishment and maintenance in plants, we performed a forward genetic screening of PIN2:PIN1-HA;pin2 Arabidopsis (Arabidopsis thaliana) plants, which ectopically express predominantly basally localized PIN1 in root epidermal cells, leading to agravitropic root growth. We identified the regulator of PIN polarity 12 (repp12) mutation, which restored gravitropic root growth and caused a switch in PIN1-HA polarity from the basal to apical side of root epidermal cells. Next Generation Sequencing and complementation experiments established the causative mutation of repp12 as a single amino acid exchange in Aminophospholipid ATPase3 (ALA3), a phospholipid flippase predicted to function in vesicle formation. repp12 and ala3 T-DNA mutants show defects in many auxin-regulated processes, asymmetric auxin distribution, and PIN trafficking. Analysis of quintuple and sextuple mutants confirmed the crucial roles of ALA proteins in regulating plant development as well as PIN trafficking and polarity. Genetic and physical interaction studies revealed that ALA3 functions together with the ADP ribosylation factor GTPase exchange factors GNOM and BIG3 in regulating PIN polarity, trafficking, and auxin-mediated development.

Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors

We demonstrate the first electrically injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2–HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 μm shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10°. This demonstration of a TiO2–HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.

Toward a 3D model of phyllotaxis based on a biochemically plausible auxin-transport mechanism.

Polar auxin transport lies at the core of many self-organizing phenomena sustaining continuous plant organogenesis. In angiosperms, the shoot apical meristem is a potentially unique system in which the two main modes of auxin-driven patterning—convergence and canalization—co-occur in a coordinated manner and in a fully three-dimensional geometry. In the epidermal layer, convergence points form, from which auxin is canalized towards inner tissue. Each of these two patterning processes has been extensively investigated separately, but the integration of both in the shoot apical meristem remains poorly understood. We present here a first attempt of a three-dimensional model of auxin-driven patterning during phyllotaxis. We base our simulations on a biochemically plausible mechanism of auxin transport proposed by Cieslak et al. (2015) which generates both convergence and canalization patterns. We are able to reproduce most of the dynamics of PIN1 polarization in the meristem, and we explore how the epidermal and inner cell layers act in concert during phyllotaxis. In addition, we discuss the mechanism by which initiating veins connect to the already existing vascular system.

Genetic screen for factors mediating PIN polarization in gravistimulated Arabidopsis thaliana hypocotyls.

SummaryGravitropism is an adaptive response that orients plant growth parallel to the gravity vector. Asymmetric distribution of the phytohormone auxin is a necessary prerequisite to the tropic bending both in roots and shoots. During hypocotyl gravitropic response, the PIN3 auxin transporter polarizes within gravity‐sensing cells to redirect intercellular auxin fluxes. First gravity‐induced PIN3 polarization to the bottom cell membranes leads to the auxin accumulation at the lower side of the organ, initiating bending and, later, auxin feedback‐mediated repolarization restores symmetric auxin distribution to terminate bending. Here, we performed a forward genetic screen to identify regulators of both PIN3 polarization events during gravitropic response. We searched for mutants with defective PIN3 polarizations based on easy‐to‐score morphological outputs of decreased or increased gravity‐induced hypocotyl bending. We identified the number of hypocotyl reduced bending (hrb) and hypocotyl hyperbending (hhb) mutants, revealing that reduced bending correlated typically with defective gravity‐induced PIN3 relocation whereas all analyzed hhb mutants showed defects in the second, auxin‐mediated PIN3 relocation. Next‐generation sequencing‐aided mutation mapping identified several candidate genes, including SCARECROW and ACTIN2, revealing roles of endodermis specification and actin cytoskeleton in the respective gravity‐ and auxin‐induced PIN polarization events. The hypocotyl gravitropism screen thus promises to provide novel insights into mechanisms underlying cell polarity and plant adaptive development.

Phase-field modeling of domain evolution in ferroelectric materials in the presence of defects

The properties of ferroelectric devices are strongly influenced, besides crystallographic features, by defects in the material. To study this effect, a fully coupled electromechanical phase-field model for 2D ferroelectric volume elements has been developed and implemented in a Finite Element code. Different kinds of defects were considered: holes, point charges and polarization pinning in single crystals, as well as grain boundaries in polycrystals, without and with additional dielectric interphase. The impact of the various types of defects on the domain configuration and the overall coercive field strength is discussed in detail. It can be seen that defects lead to nucleation of new domains. Compared to the energy barrier for switching in an ideal single crystal, the overall coercive field strength is significantly reduced towards realistic values as they are found in ferroelectric devices. Also the simulated hysteresis loops show a more realistic shape in the presence of defects.

Class XI Myosins Contribute to Auxin Response and Senescence-Induced Cell Death in Arabidopsis.

The integrity and dynamics of actin cytoskeleton is necessary not only for plant cell architecture but also for membrane trafficking-mediated processes such as polar auxin transport, senescence, and cell death. In Arabidopsis, the inactivation of actin-based molecular motors, class XI myosins, affects the membrane trafficking and integrity of actin cytoskeleton, and thus causes defective plant growth and morphology, altered lifespan and reduced fertility. To evaluate the potential contribution of class XI myosins to the auxin response, senescence and cell death, we followed the flower and leaf development in the triple gene knockout mutant xi1 xi2 xik (3KO) and in rescued line stably expressing myosin XI-K:YFP (3KOR). Assessing the development of primary inflorescence shoots we found that the 3KO plants produced more axillary branches. Exploiting the auxin-dependent reporters DR5::GUS and IAA2::GUS, a significant reduction in auxin responsiveness was found throughout the development of the 3KO plants. Examination of the flower development of the plants stably expressing the auxin transporter PIN1::PIN1-GFP revealed partial loss of PIN1 polarization in developing 3KO pistils. Surprisingly, the stable expression of PIN1::PIN1-GFP significantly enhanced the semi-sterile phenotype of the 3KO plants. Further we investigated the localization of myosin XI-K:YFP in the 3KOR floral organs and revealed its expression pattern in floral primordia, developing pistils, and anther filaments. Interestingly, the XI-K:YFP and PIN1::PIN1-GFP shared partially overlapping but distinct expression patterns throughout floral development. Assessing the foliar development of the 3KO plants revealed increased rosette leaf production with signs of premature yellowing. Symptoms of the premature senescence correlated with massive loss of chlorophyll, increased cell death, early plasmolysis of epidermal cells, and strong up-regulation of the stress-inducible senescence-associated gene SAG13 in 3KO plants. Simultaneously, the reduced auxin responsiveness and premature leaf senescence were accompanied by significant anthocyanin accumulation in 3KO tissues. Collectively, our results provide genetic evidences that Arabidopsis class XI myosins arrange the flower morphogenesis and leaf longevity via contributing to auxin responses, leaf senescence, and cell death.

Ectopic BASL Reveals Tissue Cell Polarity throughout Leaf Development in Arabidopsis thaliana

SummaryTissue-wide polarity fields, in which cell polarity is coordinated across the tissue, have been described for planar organs such as the Drosophila wing and are considered important for coordinating growth and differentiation [1]. In planar plant organs, such as leaves, polarity fields have been identified for subgroups of cells, such as stomatal lineages [2], trichomes [3, 4], serrations [5], or early developmental stages [6]. Here, we show that ectopic induction of the stomatal protein BASL (BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE) reveals a tissue-wide epidermal polarity field in leaves throughout development. Ectopic GFP-BASL is typically localized toward the proximal end of cells and to one lobe of mature pavement cells, revealing a polarity field that aligns with the proximodistal axis of the leaf (base to tip). The polarity field is largely parallel to the midline of the leaf but diverges in more lateral positions, particularly at later stages in development, suggesting it may be deformed during growth. The polarity field is observed in the speechless mutant, showing that it is independent of stomatal lineages, and is observed in isotropic cells, showing that cell shape anisotropy is not required for orienting polarity. Ectopic BASL forms convergence and divergence points at serrations, mirroring epidermal PIN polarity patterns, suggesting a common underlying polarity mechanism. Thus, we show that similar to the situation in animals, planar plant organs have a tissue-wide cell polarity field, and this may provide a general cellular mechanism for guiding growth and differentiation.

The Arabidopsis USL1 controls multiple aspects of development by affecting late endosome morphology.

Summary The polar transport of auxin controls many aspects of plant development. However, the molecular mechanisms underlying auxin tranport regulation remain to be further elucidated.We identified a mutant named as usl1 (unflattened and small leaves) in a genetic screen in Arabidopsis thaliana. The usl1 displayed multiple aspects of developmental defects in leaves, embryogenesis, cotyledons, silique phyllotaxy and lateral roots in addition to abnormal leaves. USL1 encodes a protein orthologous to the yeast vacuolar protein sorting (Vps) 38p and human UV RADIATION RESISTANCE‐ASSOCIATED GENE (UVRAG). Cell biology, Co‐IP/MS and yeast two‐hybrid were used to identify the function of USL1.USL1 colocalizes at the subcellular level with VPS29, a key factor of the retromer complex that controls auxin transport. The morphology of the VPS29‐associated late endosomes (LE) is altered from small dots in the wild‐type to aberrant enlarged circles in the usl1 mutants. The usl1 mutant synergistically interacts with vps29. We also found that USL1 forms a complex with AtVPS30 and AtVPS34.We propose that USL1 controls multiple aspects of plant development by affecting late endosome morphology and by regulating the PIN1 polarity. Our findings provide a new layer of the understanding on the mechanisms of plant development regulation.