Distal Transition Zone Research Articles

Eurasian Arctic Rifted Margin Composite Tectono-Sedimentary Element

The Eurasian Arctic Rifted Margin (EARM) spans a poorly studied transition region between the Eurasian continental shelf and the deep-water Nansen Basin. It is a conjugate margin to the Lomonosov Ridge, as both domains were united before the opening of the oceanic Eurasia Basin. The EARM is considered as a Composite Tectono-Sedimentary Element (CTSE) consisting of two individual tectono-sedimentary elements (TSEs): (1) an undefined group of poorly known pre-rift Mesozoic and Paleozoic sedimentary successions; and (2) Late Cretaceous–Paleocene synrift strata. The latter are bounded by a c. 56 Ma break-up unconformity and are overlain by the Eurasia Basin prograded margin TSE, which is not included in EARM. In the absence of drilled wells, we utilize multichannel seismic reflection (MCS) data for seismic stratigraphic correlations with nearby, better-explored, areas. The EARM CTSE is subdivided into three along-strike segments (from west to east): Svalbard–Barents Sea, the North Kara Sea and the Taimyr–Laptev Sea. Across-strike, the EARM CTSE is composed of a proximal zone of stretched crust characterized by normal faulting and a relatively narrow distal transition zone that may contain unroofed serpentinized mantle. The lack of drilled wells makes it challenging to evaluate the petroleum potential of the CTSE, although some indications of a working petroleum system presence exist.

Anatomy of the hinge region of the petiole of prostrate leaves of the wintergreen fern Polystichum acrostichoides (Dryopteridaceae)

The reorientation of leaves of Polystichum acrostichoides (Michx.) Schott to a prostrate position is achieved by forming a hinge region near the base of the petiole. Anatomical details of the distal transition zone (DTZ), folding zone (FZ), and proximal transition zone (PTZ) of the hinge region were studied using light microscopy. Data showed that the vascular bundles (VBs) are intact throughout the hinge region. Towards the FZ, the DTZ and PTZ have an increasing number of cortical cells that underwent deformation and protoplast degeneration, and cell nuclei are apparent in strongly deformed cortical cells. In the FZ, the petiole is compressed, having a network of cell walls of dead cortical cells with patches of turgid cortical cells, and largely intact endodermis surrounding the VBs. The helical secondary wall thickenings of the protoxylem and scalariform thickenings of the metaxylem may contribute to the flexibility of the VBs. This study provided evidence for the deformation and degeneration of cortical cells, which is responsible for the loss of turgidity of the hinge region while their cell walls may provide cushioning during bending and insulation for the living tissues under the snowpack, illustrating a unique strategy of ferns to adapt to a cold environment.

The Early Outcomes of BeGraft Peripheral Plus in Branched Endovascular Repair of Thoracoabdominal Aneurysms

Objective No bridging stent-graft (BSG) has been specifically designed for branched endovascular aortic repair (BEVAR) and therefore different “off-label” stent-grafts have been used. Recently, a third generation of balloon-expandable stent-graft has become available. Here we evaluate the outcomes of the BeGraft Peripheral Plus (B+) used as a BSG for internal/externalor inner branches during BEVAR. Materials and Methods Consecutive patients undergoing BEVAR using B+ as a BSG since its release in 2017 were included into the study. The primary endpoints were technical success and target vessel patency during follow-up. Secondary endpoints included the need for adjunct extension and relining of the BSG, branch instability rate, including occlusion, reinterventions for restonosis, kink, fracture, or endoleak (types 1 and 3). Results A total of 163 visceral branches in 46 patients were included with a median follow-up 15 months (4–36 months). Primary technical success was achieved in all visceral branches (69 inner branches and 94 internal/external branches) with the exception of 1 BSG that required serial dilatation until full expansion was achieved with overall branch patency was 98% at 2 years. An additional stent-graft was necessary in 35 branches (21%) following deployment of a B+ BSG to cover a longer bridging distance and optimize the distal and proximal sealing. Relining of B+ BSG was not routinely carried out during the index procedure and a self-expanding uncovered nitinol stent was necessary in only 3% of branches to smooth the distal transition zone between the BSG and target vessel. There were 4 events (2.4%) of branch related instability, including 2 occlusions and 2 late reinterventions for a partial in-stent-graft thrombosis. Conclusion Our study findings show satisfactory early outcomes of B+ as a BSG in BEVAR with low occlusion and reintervention rates. Extensions of BSG might be required to achieve adequate seal in the target vessels but routine relining BSG in branches was not required.

A multidrug and toxic compound extrusion (MATE) transporter modulates auxin levels in root to regulate root development and promotes aluminium tolerance.

MATE (multidrug and toxic compound extrusion) transporters play multiple roles in plants including detoxification, secondary metabolite transport, aluminium (Al) tolerance, and disease resistance. Here we identify and characterize the role of the Arabidopsis MATE transporter DETOXIFICATION30. AtDTX30 regulates auxin homeostasis in Arabidopsis roots to modulate root development and Al-tolerance. DTX30 is primarily expressed in roots and localizes to the plasma membrane of root epidermal cells including root hairs. dtx30 mutants exhibit reduced elongation of the primary root, root hairs, and lateral roots. The mutant seedlings accumulate more auxin in their root tips indicating role of DTX30 in maintaining auxin homeostasis in the root. Al induces DTX30 expression and promotes its localization to the distal transition zone. dtx30 seedlings accumulate more Al in their roots but are hyposensitive to Al-mediated rhizotoxicity perhaps due to saturation in root growth inhibition. Increase in expression of ethylene and auxin biosynthesis genes in presence of Al is absent in dtx30. The mutants exude less citrate under Al conditions, which might be due to misregulation of AtSTOP1 and the citrate transporter AtMATE. In conclusion, DTX30 modulates auxin levels in root to regulate root development and in the presence of Al indirectly modulates citrate exudation to promote Al tolerance.

Single-particle tracking localization microscopy reveals nonaxonemal dynamics of intraflagellar transport proteins at the base of mammalian primary cilia.

Primary cilia play a vital role in cellular sensing and signaling. An essential component of ciliogenesis is intraflagellar transport (IFT), which is involved in IFT protein recruitment, axonemal engagement of IFT protein complexes, and so on. The mechanistic understanding of these processes at the ciliary base was largely missing, because it is challenging to observe the motion of IFT proteins in this crowded region using conventional microscopy. Here, we report short-trajectory tracking of IFT proteins at the base of mammalian primary cilia by optimizing single-particle tracking photoactivated localization microscopy for IFT88-mEOS4b in live human retinal pigment epithelial cells. Intriguingly, we found that mobile IFT proteins “switched gears” multiple times from the distal appendages (DAPs) to the ciliary compartment (CC), moving slowly in the DAPs, relatively fast in the proximal transition zone (TZ), slowly again in the distal TZ, and then much faster in the CC. They could travel through the space between the DAPs and the axoneme without following DAP structures. We further revealed that BBS2 and IFT88 were highly populated at the distal TZ, a potential assembly site. Together, our live-cell single-particle tracking revealed region-dependent slowdown of IFT proteins at the ciliary base, shedding light on staged control of ciliary homeostasis.

Transcriptional Regulation of Aluminum-Tolerance Genes in Higher Plants: Clarifying the Underlying Molecular Mechanisms.

Aluminum (Al) rhizotoxicity is one of the major environmental stresses that decrease global food production. Clarifying the molecular mechanisms underlying Al tolerance may contribute to the breeding of Al-tolerant crops. Recent studies identified various Al-tolerance genes. The expression of these genes is inducible by Al. Studies of the major Arabidopsis thaliana Al-tolerance gene, ARABIDOPSIS THALIANA ALUMINUM-ACTIVATED MALATE TRANSPORTER 1 (AtALMT1), which encodes an Al-activated malate transporter, revealed that the Al-inducible expression is regulated by a SENSITIVE TO PROTON RHIXOTOXICITY 1 (STOP1) zinc-finger transcription factor. This system, which involves STOP1 and organic acid transporters, is conserved in diverse plant species. The expression of AtALMT1 is also upregulated by several phytohormones and hydrogen peroxide, suggesting there is crosstalk among the signals involved in the transcriptional regulation of AtALMT1. Additionally, phytohormones and reactive oxygen species (ROS) activate various transcriptional responses, including the expression of genes related to increased Al tolerance or the suppression of root growth under Al stress conditions. For example, Al suppressed root growth due to abnormal accumulation of auxin and cytokinin. It activates transcription of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 and other phytohormone responsive genes in distal transition zone, which causes suppression of root elongation. On the other hand, overexpression of Al inducible genes for ROS-detoxifying enzymes such as GLUTATHIONE–S-TRANSFERASE, PEROXIDASE, SUPEROXIDE DISMUTASE enhances Al resistance in several plant species. We herein summarize the complex transcriptional regulation of an Al-inducible genes affected by STOP1, phytohormones, and ROS.

Sfr1, a Tetrahymena thermophila Sfi1 Repeat Protein, Modulates the Production of Cortical Row Basal Bodies.

Basal bodies are essential microtubule-based structures that template, anchor, and orient cilia at the cell surface. Cilia act primarily in the generation of directional fluid flow and sensory reception, both of which are utilized for a broad spectrum of cellular processes. Although basal bodies contribute to vital cell functions, the molecular contributors of their assembly and maintenance are poorly understood. Previous studies of the ciliate Tetrahymena thermophila revealed important roles for two centrin family members in basal body assembly, separation of new basal bodies, and stability. Here, we characterize the basal body function of a centrin-binding protein, Sfr1, in Tetrahymena. Sfr1 is part of a large family of 13 proteins in Tetrahymena that contain Sfi1 repeats (SFRs), a motif originally identified in Saccharomyces cerevisiae Sfi1 that binds centrin. Sfr1 is the only SFR protein in Tetrahymena that localizes to all cortical row and oral apparatus basal bodies. In addition, Sfr1 resides predominantly at the microtubule scaffold from the proximal cartwheel to the distal transition zone. Complete genomic knockout of SFR1 (sfr1Δ) causes a significant increase in both cortical row basal body density and the number of cortical rows, contributing to an overall overproduction of basal bodies. Reintroduction of Sfr1 into sfr1Δ mutant cells leads to a marked reduction of cortical row basal body density and the total number of cortical row basal bodies. Therefore, Sfr1 directly modulates cortical row basal body production. This study reveals an inhibitory role for Sfr1, and potentially centrins, in Tetrahymena basal body production. IMPORTANCE Basal bodies and centrioles are structurally similar and, when rendered dysfunctional as a result of improper assembly or maintenance, are associated with human diseases. Centrins are conserved and abundant components of both structures whose basal body and centriolar functions remain incompletely understood. Despite the extensive study of centrins in Tetrahymena thermophila, little is known about how centrin-binding proteins contribute to centrin's roles in basal body assembly, stability, and orientation. The sole previous study of the large centrin-binding protein family in Tetrahymena revealed a role for Sfr13 in the stabilization and separation of basal bodies. In this study, we found that Sfr1 localizes to all Tetrahymena basal bodies and complete genetic deletion of SFR1 leads to overproduction of basal bodies. The uncovered inhibitory role of Sfr1 in basal body production suggests that centrin-binding proteins, as well as centrins, may influence basal body number both positively and negatively.

Targeted expression of SbMATE in the root distal transition zone is responsible for sorghum aluminum resistance

Aluminum (Al) toxicity is one of the major limiting factors for crop production on acid soils that comprise significant portions of the world's lands. Aluminum resistance in the cereal crop Sorghum bicolor is mainly achieved by Al-activated root apical citrate exudation, which is mediated by the plasma membrane localized citrate efflux transporter encoded by SbMATE. Here we precisely localize tissue- and cell-specific Al toxicity responses as well as SbMATE gene and protein expression in root tips of an Al-resistant near-isogenic line (NIL). We found that Al induced the greatest cell damage and generation of reactive oxygen species specifically in the root distal transition zone (DTZ), a region 1-3 mm behind the root tip where transition from cell division to cell elongation occurs. These findings indicate that the root DTZ is the primary region of root Al stress. Furthermore, Al-induced SbMATE gene and protein expression were specifically localized to the epidermal and outer cortical cell layers of the DTZ in the Al-resistant NIL, and the process was precisely coincident with the time course of Al induction of SbMATE expression and the onset of the recovery of roots from Al-induced damage. These findings show that SbMATE gene and protein expression are induced when and where the root cells experience the greatest Al stress. Hence, Al-resistant sorghum plants have evolved an effective strategy to precisely localize root citrate exudation to the specific site of greatest Al-induced root damage, which minimizes plant carbon loss while maximizing protection of the root cells most susceptible to Al damage.

Aluminium toxicity in plants: internalization of aluminium into cells of the transition zone in Arabidopsis root apices related to changes in plasma membrane potential, endosomal behaviour, and nitric oxide production

The extent of aluminium internalization during the recovery from aluminium stress in living roots of Arabidopsis thaliana was studied by non-invasive in vivo microscopy in real time. Aluminium exposure caused rapid depolarization of the plasma membrane. The extent of depolarization depends on the developmental state of the root cells; it was much more extensive in cells of the distal than in the proximal portion of the transition zone. Also full recovery of the membrane potential after removal of external aluminium was slower in cells of the distal transition zone than of its proximal part. Using morin, a vital marker dye for aluminium, and FM4-64, a marker for endosomal/vacuolar membranes, an extensive aluminium internalization was recorded during the recovery phase into endosomal/vacuolar compartments in the most aluminium-sensitive cells. Interestingly, aluminium interfered with FM4-64 internalization and inhibited the formation of brefeldin A-induced compartments in these cells. By contrast, there was no detectable uptake of aluminium into cells of the proximal part of the transition zone and the whole elongation region. Moreover, cells of the distal portion of the transition zone emitted large amounts of nitric oxide (NO) and this was blocked by aluminium treatment. These data suggest that aluminium internalization is related to the most sensitive status of the distal portion of the transition zone towards aluminium. Aluminium in these root cells has impact on endosomes and NO production.

Root cell patterning: a primary target for aluminium toxicity in maize

The short-term influence (5-180 min) of 50 microM Al on cell division was investigated in root tips of two Zea mays L. varieties differing in Al-resistance. The incorporation of bromodeoxyuridine into S-phase nuclei was visualized by immunofluorescence staining using confocal laser fluorescence microscopy. In Al-sensitive plants 5 min Al exposure was enough to inhibit cell division in the proximal meristem (250-800 microm from the tip). After 10 or 30 min with Al only, a few S-phase nuclei were found in the cortical initials. By contrast, cell division was stimulated in the distal elongation zone (2.5-3.1 mm). After 180 min the protrusion of an incipient lateral root was observed in this zone. These observations suggest a fast change in cell patterning rather than a general cariotoxic effect after exposure to Al for a short time. No such changes were found in Al-resistant maize. This is the first report showing such fast Al-induced alterations in the number and the position of dividing cells in root tips. The observation that similar changes were induced by a local supply of naphthylphthalamic acid to the distal transition zone suggests that inhibition of auxin transport plays a role in the Al-induced alteration of root cell patterning.

Genotypical differences in aluminum resistance of maize are expressed in the distal part of the transition zone. Is reduced basipetal auxin flow involved in inhibition of root elongation by aluminum?

Short-term Al treatment (90 microM Al at pH 4.5 for 1 h) of the distal transition zone (DTZ; 1-2 mm from the root tip), which does not contribute significantly to root elongation, inhibited root elongation in the main elongation zone (EZ; 2.5-5 mm from the root tip) to the same extent as treatment of the entire maize (Zea mays) root apex. Application of Al to the EZ had no effect on root elongation. Higher genotypical resistance to Al applied to the entire root apex, and specifically to the DTZ, was expressed by less inhibition of root elongation, Al accumulation, and Al-induced callose formation, primarily in the DTZ. A characteristic pH profile along the surface of the root apex with a maximum of pH 5.3 in the DTZ was demonstrated. Al application induced a substantial flattening of the pH profile moreso in the Al-sensitive than in the Al-resistant cultivar. Application of indole-3-acetic acid to the EZ but not to the meristematic zone significantly alleviated the inhibition of root elongation induced by the application of Al to the DTZ. Basipetal transport of exogenously applied [(3)H]indole-3-acetic acid to the meristematic zone was significantly inhibited by Al application to the DTZ in the Al-sensitive maize cv Lixis. Our results provide evidence that the primary mechanisms of genotypical differences in Al resistance are located within the DTZ, and suggest a signaling pathway in the root apex mediating the Al signal between the DTZ and the EZ through basipetal auxin transport.

The Blepharoplast of the Midstage Spermatid of Andreaeobryum macrosporum (Bryophyta: Andreaeopsida)

The blepharoplast of the midstage spermatid of Andreaeobryum macrosporum has a four-layered multilayered structure (MLS) and two superposed, slightly staggered, and overlapping basal bodies. The spline is composed of 30 parallel microtubules at its maximum width. Subtending the spline anteriorly, the lamellar strip (LS) is 1.83 pm long and 0.92 pm wide and has an elongated, wedge-shape with a pointed right anterior tip. Viewing the blepharoplast dorsally from anterior to posterior, the anterior basal body (ABB), approximately 0.95 pm in length, is situated over the right side of the MLS and is inserted at a level 0.42 pCm behind the spline's anterior apex. The posterior basal body (PBB), 2.75 pcm long, is positioned over the left side of the MLS and inserted 0.75 pm behind the spline's anterior apex. The ABB is essentially parallel with the spline microtubules over its entire length, while the anterior portion of the PBB curves outward gradually and becomes parallel with the spline in its posterior region. The combination of features that distinguish the midstage spermatid of Andreaeobryum from other mosses are its wide spline, wedge-shaped lamellar strip, comparatively short basal bodies, small length of stagger between basal bodies, and the PBB that curves gradually outward from its anterior tip. The data available for Andreaea suggest that its midstage spermatid resembles that of Andreaeobryum, although reconstructions and additional micrographic data are needed for both Andreaea and Takakia before generalizations for the class Andreaeopsida can be made. Andreaeobryum belongs to an unusual line of bryophyte evolution that also includes Andreaea and Takakia (Murray 1988; Renzaglia et al. 1991). While Andreaea is an old and well-established genus, Andreaeobryum is relatively new, having been described in 1976 by Steere and Murray (1976) and further defined by Murray (1988). Andreaea and Andreaeobryum have been grouped together in either the class Andreaeopsida (Crum & Anderson 1981; Murray 1988) or subclass Andreaeidae (Schofield 1985; Vitt 1984). According to Murray (1988), Andreaea and Andreaeobryum belong to separate orders, Andreaeales and Andreaeobryales, within the primitive class Andreaeopsida. The two genera are united by sporeling features and mode SAuthor for correspondence. e-mail: AnnRushing@ baylor.edu FIGUREs 1-6. Blepharoplast anatomy of Andreaeobryum macrosporum. -1-3. Tangential sections. -1. The spline anterior with its acutely curved left margin and closed aperture. Above, the extended triplet is part of the posterior basal body (cf. Fig. 18). -2. Slightly oblique section showing the left-marginal curvature of the subtending lamellar strip and the spline aperture (between arrows). -3. The spline aperture extends posteriorly beyond the lamellar strip where it closes by convergence of the microtubules on its right side with those on the left. -4. Near-median longitudinal section through the anterior basal body and the distal transition zone with its stellate pattern. The anterior mitochondrion is just becoming positioned beneath the lamellar strip. -5. Oblique-tangential section showing the full longitudinal extent of the anterior stellate pattern. -6. Oblique-tangential section section through the posterior basal body and the subtending spline and nucleus. Key to labeling: ABB, anterior basal body; AF, anterior flagellum; AM, anterior mitochondrion; ASP, anterior stellate pattern; EH, extended hub of basal body; ET, extended triplet; LS, lamellar strip; N, nucleus; PBB, posterior basal body; PSP, posterior stellate pattern; S, spline; S1-S4, specific strata of the multilayered structure; SA, spline aperture; bracket ([), lamellar strip. All micrographs are printed at a magnification of X67,500 except Fig. 6 where the magnification is X47,500. Except as otherwise noted for Figure 18, each scale bar represents