Selective REcruitmeNt of plant DNA polymerases by geminivirus.

Geminiviruses reprogram host machineries to ensure their own propagation. They do not encode any DNA polymerase. Furthermore, the absence of direct evidence about the precise role of any host-encoded DNA polymerase has made geminivirus replication an enigma. Wu et al. recently resolved this puzzle by revealing that geminiviruses utilize plant DNA polymerase α and δ to drive their replication.

Application of machine learning in understanding plant virus pathogenesis: trends and perspectives on emergence, diagnosis, host-virus interplay and management.

BACKGROUND: Inclusion of high throughput technologies in the field of biology has generated massive amounts of data in the recent years. Now, transforming these huge volumes of data into knowledge is the primary challenge in computational biology. The traditional methods of data analysis have failed to carry out the task. Hence, researchers are turning to machine learning based approaches for the analysis of high-dimensional big data. In machine learning, once a model is trained with a training dataset, it can be applied on a testing dataset which is independent. In current times, deep learning algorithms further promote the application of machine learning in several field of biology including plant virology. MAIN BODY: Plant viruses have emerged as one of the principal global threats to food security due to their devastating impact on crops and vegetables. The emergence of new viral strains and species help viruses to evade the concurrent preventive methods. According to a survey conducted in 2014, plant viruses are anticipated to cause a global yield loss of more than thirty billion USD per year. In order to design effective, durable and broad-spectrum management protocols, it is very important to understand the mechanistic details of viral pathogenesis. The application of machine learning enables precise diagnosis of plant viral diseases at an early stage. Furthermore, the development of several machine learning-guided bioinformatics platforms has primed plant virologists to understand the host-virus interplay better. In addition, machine learning has tremendous potential in deciphering the pattern of plant virus evolution and emergence as well as in developing viable control options. CONCLUSIONS: Considering a significant progress in the application of machine learning in understanding plant virology, this review highlights an introductory note on machine learning and comprehensively discusses the trends and prospects of machine learning in the diagnosis of viral diseases, understanding host-virus interplay and emergence of plant viruses.

Molecular interplay between phytohormones and geminiviruses: a saga of a never-ending arms race.

Geminiviruses can infect a wide range of plant hosts worldwide and have hence become an emerging global agroeconomic threat. The association of these viruses with satellite molecules and highly efficient insect vectors such as whiteflies further prime their devastating impacts. Plants elicit a strong antiviral immune response to restrict the invasion of these destructive pathogens. Phytohormones help plants to mount this response and occupy a key position in combating these biotrophs. These defense hormones not only inhibit geminiviral propagation but also hamper viral transmission by compromising the performance of their insect vectors. Nonetheless, geminiviruses have co-evolved to have a few multitasking virulence factors that readily remodel host cellular machineries to circumvent the phytohormone-mediated manifestation of the immune response. Furthermore, these obligate parasites exploit plant growth hormones to produce a cellular environment permissive for virus replication. In this review, we outline the current understanding of the roles and regulation of phytohormones in geminiviral pathogenesis.

Unraveling the Charge Transport Mechanism in Mechanochemically Processed Hybrid Perovskite Solar Cell.

The long-term operation of organic-inorganic hybrid perovskite solar cells is hampered by the microscopic strain introduced by the multiple thermal cycles during the synthesis of the material via a solution process route. This setback can be eliminated by a room temperature synthesis scheme. In this work, a mechanochemical synthesis technique at room temperature is employed to process CH3NH3PbI2Br films for fabricating perovskite solar cell devices. The solar cell device has produced a 957 mV Voc, a 16.92 mA/cm2 short circuit current density, and a 10.5% efficiency. These values are higher than the published values on mechanochemically synthesized CH3NH3PbI3. The charge transport properties of the devices are studied using DC conductivity and AC impedance spectroscopy, which show a multichannel transport mechanism having both ionic and electronic contributions. A much smaller defect density in the mechanochemically synthesized hybrid perovskite material is confirmed. A polarization assisted recombination mechanism is observed to have a dominant effect on the overall charge transport mechanism. However, no obvious grain boundary and intralayer lattice defect related responses are found in the perovskite layer. Interfacial charge transport and recombination are found to show major effects on both the temperature dependent and illumination dependent impedance spectra.

Impact of viral silencing suppressors on plant viral synergism: a global agro-economic concern.

Plant viruses are known for their devastating impact on global agriculture. These intracellular biotrophic pathogens can infect a wide variety of plant hosts all over the world. The synergistic association of plant viruses makes the situation more alarming. It usually promotes the replication, movement, and transmission of either or both the coexisting synergistic viral partners. Although plants elicit a robust antiviral immune reaction, including gene silencing, to limit these infamous invaders, viruses counter it by encoding viral suppressors of RNA silencing (VSRs). Growing evidence also suggests that VSRs play a driving role in mediating the plant viral synergism. This review briefly discusses the evil impacts of mixed infections, especially synergism, and then comprehensively describes the emerging roles of VSRs in mediating the synergistic association of plant viruses. KEY POINTS: • Synergistic associations of plant viruses have devastating impacts on global agriculture. • Viral suppressors of RNA silencing (VSRs) play key roles in driving plant viral synergism.

Interface Engineering in Quantum-Dot-Sensitized Solar Cells.

The unique properties of II-VI semiconductor nanocrystals such as superior light absorption, size-dependent optoelectronic properties, solution processability, and interesting photophysics prompted quantum-dot-sensitized solar cells (QDSSCs) as promising candidates for next-generation photovoltaic (PV) technology. QDSSCs have advantages such as low-cost device fabrication, multiple exciton generation, and the possibility to push over the theoretical power conversion efficiency (PCE) limit of 32%. In spite of dedicated research efforts to enhance the PCE, optimize individual solar cell components, and better understand the underlying science, QDSSCs have unfortunately not lived up to their potential due to shortcomings in the fabrication process and with the QDs themselves. In this feature article, we briefly discuss the QDSSC concepts and mechanisms of the charge carrier recombination pathways that occur at multiple interfaces, viz., (i) metal oxide (MO)/QDs, (ii) MO/QDs/electrolyte, and (iii) counter electrode (CE)/electrolyte. The rational strategies that have been developed to minimize/block these charge recombination pathways are elaborated. The article concludes with a discussion of the present challenges in fabricating efficient devices and future prospects for QDSSCs.

Targeting NPR1: a strategy went viral.

Non-expressor of pathogenesis-related 1 (NPR1) acts as master regulator of plant immunity by promoting salicylic acid (SA) signalling. Some bacterial and fungal pathogens target NPR1 to inhibit SA-mediated immunity. Recently, Zhang et al. and Liu et al. demonstrated that a diverse spectrum of plant-infecting viruses have evolved distinct counter-defence strategies to weaken NPR1-mediated antiviral defence.

'Rewritable' and 'liquid-specific' recognizable wettability pattern.

Bio-inspired surfaces with wettability patterns display a unique ability for liquid manipulations. Sacrificing anti-wetting property for confining liquids irrespective of their surface tension (γLV), remains a widely accepted basis for developing wettability patterns. In contrast, we introduce a 'liquid-specific' wettability pattern through selectively sacrificing the slippery property against only low γLV (<30 mN m-1) liquids. This design includes a chemically reactive crystalline network of phase-transitioning polymer, which displays an effortless sliding of both low and high γLV liquids. Upon its strategic chemical modification, droplets of low γLV liquids fail to slide, rather spill arbitrarily on the tilted interface. In contrast, droplets of high γLV liquids continue to slide on the same modified interface. Interestingly, the phase-transition driven rearrangement of crystalline network allows to revert the slippery property against low γLV liquids. Here, we report a 'rewritable' and 'liquid-specific' wettability pattern for high throughput screening, separating, and remoulding non-aqueous liquids.

Lattice strain induced d-band centre engineering enabled pseudocapacitive energy storage in 2D hypo-hyper electronic V-NiCo2O4 for asymmetric supercapacitors.

Understanding the role of fundamental structural engineering of materials in unravelling the underlying rudimentary electronic structure-dependent charge storage mechanisms is crucial for developing new strategic approaches toward high-performance electrochemical energy storage devices. Here, we demonstrate the role of strain engineering by V doping-induced lattice contraction in NiCo2O4 for increasing the energy density and power density of aqueous asymmetric hybrid supercapacitors. For application in energy storage, we demonstrate the influence of electron-deficient V4+/5+ doping in electron-rich Ni2+ sites, which has been found to result in the formation of a hypo-hyper electronically coupled cation pair causing a shift in the d-band and O 2p band centres and distortion of CoO6 octahedra. Optimization of V doping to 3 mol%, achieved by a binder-free one-step hydrothermal method, has yielded a 96% increase in specific capacitance of up to 2316 F g-1 from 1193 F g-1 in pristine materials at 1 A g-1 in a three-electrode configuration with a coulombic efficiency (η%) of 94% and a 24% increase in rate capacity. A two-fold increase in specific capacitance in the pouch cell device, fabricated with a functionalized carbon nanosphere positive electrode, has been observed for the V-doped samples at 1 A g-1 with a η% of 97% and a maximum energy density of 96.3 W h g-1 and a maximum power density of 8733.6 W g-1 which are 41% and 24.3% higher than the pristine device, respectively. Excellent cycling stability of 95.4% capacitance retention has been observed after 6000 cycles. DFT calculations have been carried out to understand the previously unexplored effect of lattice strain on charge transport and quantum capacitance, and ultimately its effect on the transition state kinetics of energy storage faradaic reaction mechanisms. The aim of this work is to establish a fresh perspective on developing a deep understanding of the fundamental electronic and structural properties of materials by drawing in concepts from descriptor models in electrocatalysis to reveal the role of lattice strain and d-band centre tailoring in enabling pseudocapacitive energy storage.

Unravelling Rashba-Dresselhaus Splitting Assisted Magneto-Photoelectrochemical Water Splitting in Asymmetric MoSSe-GaN Heterostructures.

Among two-dimensional (2D) materials, asymmetric Janus structures (MoSSe, WSSe) have many exciting properties, such as out-of-plane piezoelectricity, spatial isolation of charge carriers, and strong spin-orbit coupling (SOC), resulting in a significant Rashba effect. However, the experimental validation to utilize SOC along with advanced optical properties for catalytic applications remains unexplored. Herein, for the first time, we demonstrate a proof-of-concept for spin-manipulated photo-electrochemical water splitting using Janus MoSSe/GaN heterostructures under an external low magnetic field. Further, the activation with delaminated 2D-MXene (Ti3C2Tx/MoSSe/GaN) for efficient electron channeling manifests ∼1.37 times photocurrent enhancement and ∼1.50-fold enhancement in product (H2/O2) formation under a low applied magnetic field (0.4 T). The external magnetic field supports spin manipulation even under unpolarized light by a spin-to-charge conversion in Janus MoSSe/GaN heterostructures. Density functional theory simulations were performed to understand the role of the Rashba-Dresselhaus effect for efficient charge transport.

Optimization of Tobacco Rattle Virus (TRV)-Based Virus-Induced Gene Silencing (VIGS) in Tomato.

Unveiling of full genome sequence of tomato demands significant advances of tomato functional genomics. Virus-induced gene silencing (VIGS) is a well explored functional genomics tool in plant biology that exploits post transcriptional gene silencing to downregulate a desired gene. Although VIGS provides an easy and highly efficient platform to study plant gene function through reverse genetics approach, currently VIGS is more efficient in model plants like Nicotiana benthamiana, which further justifies the urgent need of a highly efficient, reliable, and reproducible VIGS protocol in crop plants such as tomato. In this chapter, we have detailed an optimized Tobacco rattle virus (TRV)-based VIGS protocol in tomato.

Capsicum-infecting begomoviruses as global pathogens: host-virus interplay, pathogenesis, and management.

Whitefly-transmitted begomoviruses are among the major threats to the cultivation of Capsicum spp. (Family: Solanaceae) worldwide. Capsicum-infecting begomoviruses (CIBs) have a broad host range and are commonly found in mixed infections, which, in turn, fuels the emergence of better-adapted species through intraspecies and interspecies recombination. Virus-encoded proteins hijack host factors to breach the well-coordinated antiviral response of plants. Epigenetic modifications of histones associated with viral minichromosomes play a critical role in this molecular arms race. Moreover, the association of DNA satellites further enhances the virulence of CIBs as the subviral agents aid the helper viruses to circumvent plant antiviral defense and facilitate expansion of their host range and disease development. The objective of this review is to provide a comprehensive overview on various aspects of CIBs such as their emergence, epidemiology, mechanism of pathogenesis, and the management protocols being employed for combating them.

Photodetectors with High Responsivity by Thickness Tunable Mixed Halide Perovskite Nanosheets.

Chemical transformation of typically "nonlayered" phases into two-dimensional structures remains a formidable task. Among the thickness tunable CsPbX3 (X = Br, Br/I, I) nanosheets (NSs), CsPbBr1.5I1.5 NSs with a thickness of ∼4.9 nm have structural stability superior to ∼6.8 nm CsPbI3 NSs and better hole mobility than ∼3.7 nm CsPbBr3 NSs. Moving beyond the much-explored CsPbBr3 photodetectors, we demonstrate a sharp improvement of the photodetection of CsPbBr1.5I1.5 NS devices by thickening the NSs to ∼6.1 nm through combining 8-carbon and 18-carbon ligand surfactants. Thereby, the responsivity increases up to one of the highest values of 3313 A W-1 at 1.5 V (and 3946 A W-1 at 2 V) with detectivity of 1.6 × 1011 Jones at 1.5 V, due to the increase in carrier mobility up to 7.9 × 10-4 cm2 V-1 s-1. The better device performance of the NSs than 8.6-13.9 nm nanocubes (NCs) is due to their planarity which facilitates in-plane mobilization of the charge carriers.

Metformin-Templated Nanoporous ZnO and Covalent Organic Framework Heterojunction Photoanode for Photoelectrochemical Water Oxidation.

Photoelectrochemical water-splitting offers unique opportunity in the utilization of abundant solar light energy and water resources to produce hydrogen (renewable energy) and oxygen (clean environment) in the presence of a semiconductor photoanode. Zinc oxide (ZnO), a wide bandgap semiconductor is found to crystallize predominantly in the hexagonal wurtzite phase. Herein, we first report a new crystalline triclinic phase of ZnO by using N-rich antidiabetic drug metformin as a template via hydrothermal synthesis with self-assembled nanorod-like particle morphology. We have fabricated a heterojunction nanocomposite charge carrier photoanode by coupling this porous ZnO with a covalent organic framework, which displayed highly enhanced photocurrent density of 0.62 mA/cm2 at 0.2 V vs. RHE in photoelectrochemical water oxidation and excellent photon-to-current conversion efficiency at near-neutral pH vis-à-vis bulk ZnO. This enhancement of the photocurrent for the porous ZnO/COF nanocomposite material over the corresponding bulk ZnO could be attributed to the visible light energy absorption by COF and subsequent efficient charge-carrier mobility via porous ZnO surface.

Exfoliated Molybdenum Disulfide-Wrapped CdS Nanoparticles as a Nano-Heterojunction for Photo-Electrochemical Water Splitting.

We developed a heterojunction photocathode, MoS2@CdS, based on the wrapping of CdS nanoparticles by the MoS2 nanocrystals. The liquid-phase exfoliation method was adopted for preparing few-layer MoS2 nanocrystals of a layer thickness of ∼7.9 nm, whereas CdS nanoparticles of an average diameter of ∼17 nm were synthesized by the one-step hydrothermal process. The synthesized nanocrystals and nanoparticles were characterized by AFM, FESEM, HRTEM, STEM, XRD, GIXRD, UV-vis absorption, fluorescence emission, and Raman spectroscopy. The difference between two modes in the Raman spectrum of MoS2 indicates the formation of few-layer MoS2. The photoelectrochemical performance of the heterojunction photocathode was excellent. The MoS2@CdS heterostructure photocathode increased the photocurrent density (JPh) under 100 mW/cm2 illumination. We obtained the maximum applied biased photoconversion efficiency (ABPE) of ∼1.2% of the MoS2@CdS heterojunction photocathode in optimum device configuration. The production of H2 was measured as ∼72 µmol/h for the MoS2@CdS heterostructure with a cyclic stability of up to 7500 s.

Modified p-GaN Microwells with Vertically Aligned 2D-MoS2 for Enhanced Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) water splitting has been considered as the future technology for storing solar energy in the chemical bonds. However, due to the search of ideal heterostructured materials for photoanode/cathode, the full potential of this technology has not been realized yet. Herein we present, the nanotextured hexagonal microwell of p-GaN [p-GaN(Et)] synthesized via wet chemical etching route as a photocathode (PC) for PEC water splitting. The p-GaN(Et) was further modified by interconnected nanowall network of two-dimensional (2D) transition metal dichalcogenide (MoS2) [2D-MoS2/p-GaN(Et)]. Both PCs were characterized for their morphology, structures, and optical and electronic properties. The overall PEC performance was validated through photocurrent values followed by the amount of hydrogen and oxygen evolution. This combination of 2D-MoS2/p-GaN(Et) outplayed pristine p-GaN(Et) by several orders of magnitude in overall PEC performance. The extraordinary stability under a continuous operating condition with 1 sun illumination (100 mW/cm2) provides the much-needed flavor of an efficient photocathode. The optimized photocathode [2D-MoS2/p-GaN(Et)] shows the highest applied bias photon-to-current conversion efficiency of ∼3.18% with hydrogen evolution rate of 89.56 µmol/h at -0.3 V vs RHE. This wafer-level cost-effective synthesis of 2D-MoS2/GaN heterostructure based PCs opens a new way for large-scale solar-fuel conversion.

Surface Plasmon-Enhanced Carbon Dot-Embellished Multifaceted Si(111) Nanoheterostructure for Photoelectrochemical Water Splitting.

Because of the excellent electronic properties, Si is a well-established semiconducting material for PV technology. However, slow kinetics and a fast corroding nature make Si inefficient for the hydrogen evolution reaction (HER) in photoelectrochemical (PEC) applications. Herein, we demonstrate a multifacet Si nanowire (SiNW) decorated with surface plasmon-enhanced carbon quantum dots (AuCQDs) as efficient, stable, economical, and scalable photocathodes (PCs) for HER. The PEC performance of SiNW_AuCQDs has more than a fourfold efficiency enhancement than the pristine SiNW, which we have attributed to the combined effect of enhanced solar absorption and efficient carrier transport. The optimized PC SiNW_AuCQDs results in the highest photocurrent ∼1.7 mA/cm2, an applied bias photon-to-current conversion efficiency of ∼0.8%, and H2 gas evolution rate of ∼182.93 µmol·h-1. Furthermore, these SiNW_AuCQDs PCs provide extraordinary stability under continuous operating conditions with 1 sun illumination (100 mW/cm2). The process-line compatible fabrication process of these PCs will open a new direction at the wafer-level designing of a heterostructure for large-scale solar-fuel conversion.

Chlorophyll(a)/Carbon Quantum Dot Bio-Nanocomposite Activated Nano-Structured Silicon as an Efficient Photocathode for Photoelectrochemical Water Splitting.

Solar-driven water splitting is considered as a futuristic sustainable way to generate hydrogen and chemical storage of solar energy. Further, considering the technological competence, silicon is one of the potential materials for developing large-scale and cost-effective photocathodes (PCs), but it lacks efficacy and stability. Here, we show that chlorophyll(a)/carbon quantum dots (Chl/CQDs) bio-nanocomposite (b-NC)-decorated Si-nanowires (SiNWs) as PC can surpass the reported efficiency for photoelectrochemical (PEC) hydrogen generation along with stability. The optimized heterojunction (Chl/CQDs_SiNW) significantly enhances broad-band solar absorption and protects Si surface from corrosion. Further, the appropriate band alignment enforces efficient photogenerated charge separation and possesses directional exciton transport property via the Förster resonance energy transfer (FRET) mechanism. This synergic effect demonstrates an ∼18 times increase in photocurrent density (26.36 mA/cm2) compared to pristine SiNW PC at 1.07 V vs reversible hydrogen electrode (RHE). The efficiency reaches ∼7.86%, which is comparably the highest reported for hybrid Si-based photocathodes. Hydrogen evaluation rate was measured to be ∼113 µmol/h at 0.8 V vs RHE under 1 sun illumination. With Si-process line compatibility, this new finding opens a new direction toward the development of Si-based efficient and stable PCs at a large scale for commercial applications.

Doping the Smallest Shannon Radii Transition Metal Ion Ni(II) for Stabilizing α-CsPbI3 Perovskite Nanocrystals.

Red emitting α-CsPbI3 nanocrystals are highly phase sensitive to ambient exposure, and B-site doping with suitable cations is adopted as one of the most feasible approaches for their phase stability. There are several reports herein: Ni(II) ions having the smallest transition metal Shannon radii were explored for doping in these nanocrystals. This successfully stabilized the cubic phase and retained the intense emission of nanocrystals for nearly 2 months. Being the smallest ion, the halide octahedra in the perovskite lattice were expected to provide high restraint ability toward δ-CsPbI3. Comparing with postsynthesis iodide treatments, the importance of doping in high temperature reaction was discussed. Finally, these doped nanocrystals were explored for photovoltaic devices and showed comparable efficiency (9.1%) to different other similar doped nanocrystals. Hence, the finding reported here is a step forward for understanding the insights of phase stability of α-CsPbI3 perovskite nanocrystals.

All-inorganic quantum dot assisted enhanced charge extraction across the interfaces of bulk organo-halide perovskites for efficient and stable pin-hole free perovskite solar cells.

In spite of achieving high power conversion efficiency (PCE), organo-halide perovskites suffer from long term stability issues. Especially the grain boundaries of polycrystalline perovskite films are considered as giant trapping sites for photo-generated carriers and therefore play an important role in charge transportation dynamics. Surface engineering via grain boundary modification is the most promising way to resolve this issue. A unique antisolvent-cum-quantum dot (QD) assisted grain boundary modification approach has been employed for creating monolithically grained, pin-hole free perovskite films, wherein the choice of all-inorganic CsPbBr x I3-x (x = 1-2) QDs is significant. The grain boundary filling by QDs facilitates the formation of compact films with 1-2 µm perovskite grains as compared to 300-500 nm grains in the unmodified films. The solar cells fabricated by CsPbBr1.5I1.5 QD modification yield a PCE of ∼16.5% as compared to ∼13% for the unmodified devices. X-ray photoelectron spectral analyses reveal that the sharing of electrons between the PbI6 - framework in the bulk perovskite and Br- ions in CsPbBr1.5I1.5 QDs facilitates the charge transfer process while femtosecond transient absorption spectroscopy (fs-TAS) suggests quicker trap filling and enhanced charge carrier recombination lifetime. Considerable ambient stability up to ∼720 h with <20% PCE degradation firmly establishes the strategic QD modification of bulk perovskite films.