94 research outputs found
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Resistance-gene-directed discovery of a natural-product herbicide with a new mode of action.
Bioactive natural products have evolved to inhibit specific cellular targets and have served as lead molecules for health and agricultural applications for the past century1-3. The post-genomics era has brought a renaissance in the discovery of natural products using synthetic-biology tools4-6. However, compared to traditional bioactivity-guided approaches, genome mining of natural products with specific and potent biological activities remains challenging4. Here we present the discovery and validation of a potent herbicide that targets a critical metabolic enzyme that is required for plant survival. Our approach is based on the co-clustering of a self-resistance gene in the natural-product biosynthesis gene cluster7-9, which provides insight into the potential biological activity of the encoded compound. We targeted dihydroxy-acid dehydratase in the branched-chain amino acid biosynthetic pathway in plants; the last step in this pathway is often targeted for herbicide development10. We show that the fungal sesquiterpenoid aspterric acid, which was discovered using the method described above, is a sub-micromolar inhibitor of dihydroxy-acid dehydratase that is effective as a herbicide in spray applications. The self-resistance gene astD was validated to be insensitive to aspterric acid and was deployed as a transgene in the establishment of plants that are resistant to aspterric acid. This herbicide-resistance gene combination complements the urgent ongoing efforts to overcome weed resistance11. Our discovery demonstrates the potential of using a resistance-gene-directed approach in the discovery of bioactive natural products
Research on optimization operation technology of qt oil pipeline based on the heuristic algorithm
Global environmental problems have become increasingly prominent, and China, as one of the world’s major powers, should take action. China promises to achieve a “carbon peak” by 2030, and carbon dioxide emissions will no longer increase, and will gradually decrease after reaching the peak. To achieve “carbon neutrality” by 2060, all the carbon dioxide emissions will be offset by tree planting, energy saving and emission reduction. The optimization of pipeline energy consumption is also associated with it. In recent years, the transportation mode of the QT oil pipeline has changed from normal temperature transportation to heating transportation. The energy consumption of this transportation method mainly comes from heating furnaces and pumps. In order to reduce energy consumption and find a suitable pipeline operation plan, this article optimizes and analyzes the transformed QT oil pipeline under the premise of ensuring safe production. Based on programming software, this article establishes a corresponding mathematical model of energy consumption of the QT oil pipeline, and uses artificial bee colony algorithm, invasive weed algorithm and optimization algorithm based on biogeography to solve the model. The article innovatively introduces the speed of the variable frequency pump as a variable to study the energy consumption optimization problem of the oil pipeline, analyze the practical application of the oil pipeline of the QT oil pipeline, and obtains the best plan for the optimized operation of the oil pipeline of the QT oil pipeline It provided research basis and played a role in promoting the country’s dual-carbon goals
Self-Retracting Motion of Graphite Microflakes
We report the observation of a novel phenomenon, the self-retracting motion
of graphite, in which tiny flakes of graphite, after being displaced to various
suspended positions from islands of highly orientated pyrolytic graphite,
retract back onto the islands under no external influences. Our repeated
probing and observing such flakes of various sizes indicate the existence of a
critical size of flakes, approximately 35 micrometer, above which the
self-retracting motion does not occur under the operation. This helps to
explain the fact that the self-retracting motion of graphite has not been
reported, because samples of natural graphite are typical larger than this
critical size. In fact, reports of this phenomenon have not been found in the
literature for single crystals of any kinds. A model that includes the static
and dynamic shear strengths, the van der Waals interaction force, and the edge
dangling bond interaction effect, was used to explain the observed phenomenon.
These findings may conduce to create nano-electromechanical systems with a wide
range of mechanical operating frequency from mega to giga hertzs
DDT-RELATED PROTEIN4-IMITATION SWITCH alters nucleosome distribution to relieve transcriptional silencing in Arabidopsis
DNA methylation is a conserved epigenetic modification that is typically associated with silencing of transposable elements and promoter methylated genes. However, some DNA-methylated loci are protected from silencing, allowing transcriptional flexibility in response to environmental and developmental cues. Through a genetic screen in Arabidopsis (Arabidopsis thaliana), we uncovered an antagonistic relationship between the MICRORCHIDIA (MORC) protein and the IMITATION SWITCH (ISWI) complex in regulating the DNA-methylated SUPPRESSOR OF DRM1 DRM2 CMT3 (SDC) reporter. We demonstrate that components of the plant-specific ISWI complex, including CHROMATIN REMODELING PROTEIN11 (CHR11), CHR17, DDT-RELATED PROTEIN4 (DDR4), and DDR5, function to partially de-repress silenced genes and transposable elements (TEs), through their function in regulating nucleosome distribution. This action also requires the known transcriptional activator DNAJ proteins, providing a mechanistic link between nucleosome remodeling and transcriptional activation. Genome-wide studies revealed that DDR4 causes changes in nucleosome distribution at numerous loci, a subset of which is associated with changes in DNA methylation and/or transcription. Our work reveals a mechanism for balancing transcriptional flexibility and faithful silencing of DNA-methylated loci. As both ISWI and MORC family genes are widely distributed across plant and animal species, our findings may represent a conserved eukaryotic mechanism for fine-tuning gene expression under epigenetic regulation
Chiral charge density wave and backscattering-immune orbital texture in monolayer 1T-TiTe2
Non-trivial electronic states are attracting intense attention in
low-dimensional physics. Though chirality has been identified in charge states
with a scalar order parameter, its intertwining with charge density waves
(CDW), film thickness and the impact on the electronic behaviors remain less
well understood. Here, using scanning tunneling microscopy, we report a 2 x 2
chiral CDW as well as a strong suppression of the Te-5p hole-band
backscattering in monolayer 1T-TiTe2. These exotic characters vanish in bilayer
TiTe2 with a non-CDW state. Theoretical calculations approve that chirality
comes from a helical stacking of the triple-q CDW components and therefore can
persist at the two-dimensional limit. Furthermore, the chirality renders the
Te-5p bands an unconventional orbital texture that prohibits electron
backscattering. Our study establishes TiTe2 as a promising playground for
manipulating the chiral ground states at the monolayer limit and provides a
novel path to engineer electronic properties from an orbital degree.Comment: 21 pages, 5 figure
Dichotomy of Electronic Structure and Superconductivity between Single-Layer and Double-Layer FeSe/SrTiO3 Films
The latest discovery of possible high temperature superconductivity in the
single-layer FeSe film grown on a SrTiO3 substrate, together with the
observation of its unique electronic structure and nodeless superconducting
gap, has generated much attention. Initial work also found that, while the
single-layer FeSe/SrTiO3 film exhibits a clear signature of superconductivity,
the double-layer FeSe/SrTiO3 film shows an insulating behavior. Such a dramatic
difference between the single-layer and double-layer FeSe/SrTiO3 films is
surprising and the underlying origin remains unclear. Here we report our
comparative study between the single-layer and double-layer FeSe/SrTiO3 films
by performing a systematic angle-resolved photoemission study on the samples
annealed in vacuum. We find that, like the single-layer FeSe/SrTiO3 film, the
as-prepared double-layer FeSe/SrTiO3 film is insulating and possibly magnetic,
thus establishing a universal existence of the magnetic phase in the
FeSe/SrTiO3 films. In particular, the double-layer FeSe/SrTiO3 film shows a
quite different doping behavior from the single-layer film in that it is hard
to get doped and remains in the insulating state under an extensive annealing
condition. The difference originates from the much reduced doping efficiency in
the bottom FeSe layer of the double-layer FeSe/SrTiO3 film from the FeSe-SrTiO3
interface. These observations provide key insights in understanding the origin
of superconductivity and the doping mechanism in the FeSe/SrTiO3 films. The
property disparity between the single-layer and double-layer FeSe/SrTiO3 films
may facilitate to fabricate electronic devices by making superconducting and
insulating components on the same substrate under the same condition.Comment: 19 pages, 4 figure
From Transistors to Phototransistors by Tailoring the Polymer Stacking
It is universally acknowledged that highly photosensitive transistors are strongly dependent on the high carrier mobility of polymer-based semiconductors. However, the polymer π–π stacking and aggregation, required to increase the charge mobility, conversely inhibit the dissociation of photogenerated charge carriers, in turn accelerating the geminate recombination of electron-hole pairs. To explore the effects of charge mobility and polymer stacking on the photoresponsivity of the phototransistors, here, two alternating copolymers are synthesized, namely P-PPAB-IDT and P-PPAB-BDT, by palladium-catalyzed Stille coupling of PPAB with indaceodithiophene (IDT) or benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl) (BDT) monomers. The polymer P-PPAB-IDT demonstrates a nearly 20 times enhancement in the hole mobility compared to P-PPAB-BDT. Yet, P-PPAB-IDT surprisingly shows no response to white light illumination, whereas P-PPAB-BDT exhibits a significant photoresponse to the same light source with a high light-current/dark-current (Ilight/Idark) ratio of 21.6 in the p-type area and a low current ratio of just 5.2 in the n-type area. It is believed that this work will provide an effective strategy to develop highly photosensitive polymer semiconductors by reducing polymer stacking and aggregation rather than improving the charge carrier mobility.acceptedVersionPeer reviewe
Topology hierarchy of transition metal dichalcogenides built from quantum spin Hall layers
The evolution of the physical properties of two-dimensional material from
monolayer limit to the bulk reveals unique consequences from dimension
confinement and provides a distinct tuning knob for applications. Monolayer
1T'-phase transition metal dichalcogenides (1T'-TMDs) with ubiquitous quantum
spin Hall (QSH) states are ideal two-dimensional building blocks of various
three-dimensional topological phases. However, the stacking geometry was
previously limited to the bulk 1T'-WTe2 type. Here, we introduce the novel
2M-TMDs consisting of translationally stacked 1T'-monolayers as promising
material platforms with tunable inverted bandgaps and interlayer coupling. By
performing advanced polarization-dependent angle-resolved photoemission
spectroscopy as well as first-principles calculations on the electronic
structure of 2M-TMDs, we revealed a topology hierarchy: 2M-WSe2, MoS2, and
MoSe2 are weak topological insulators (WTIs), whereas 2M-WS2 is a strong
topological insulator (STI). Further demonstration of topological phase
transitions by tunning interlayer distance indicates that band inversion
amplitude and interlayer coupling jointly determine different topological
states in 2M-TMDs. We propose that 2M-TMDs are parent compounds of various
exotic phases including topological superconductors and promise great
application potentials in quantum electronics due to their flexibility in
patterning with two-dimensional materials
Phase Diagram and High Temperature Superconductivity at 65 K in Tuning Carrier Concentration of Single-Layer FeSe Films
Superconductivity in the cuprate superconductors and the Fe-based
superconductors is realized by doping the parent compound with charge carriers,
or by application of high pressure, to suppress the antiferromagnetic state.
Such a rich phase diagram is important in understanding superconductivity
mechanism and other physics in the Cu- and Fe-based high temperature
superconductors. In this paper, we report a phase diagram in the single-layer
FeSe films grown on SrTiO3 substrate by an annealing procedure to tune the
charge carrier concentration over a wide range. A dramatic change of the band
structure and Fermi surface is observed, with two distinct phases identified
that are competing during the annealing process. Superconductivity with a
record high transition temperature (Tc) at ~65 K is realized by optimizing the
annealing process. The wide tunability of the system across different phases,
and its high-Tc, make the single-layer FeSe film ideal not only to investigate
the superconductivity physics and mechanism, but also to study novel quantum
phenomena and for potential applications.Comment: 15 pages, 4 figure
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