The molecular mechanism of efficient transmission of plant viruses in variable virus-vector-plant interactions

Plant viruses are mainly transmitted by insect vectors in the non-persistent,semi-persistent,or persistent modes.In the non-persistent mode,plant viruses are retained in the stylets of their insect vectors.In the semi-persistent mode,plant viruses are carried to vector foreguts or salivary glands,but they cannot spread to salivary glands.In the persistent mode,plant viruses are retained in vector guts and can spread to salivary glands.In the non-persistent and semi-persistent modes,plant viruses are retained for a short time and cannot enter the hemolymph of insect vectors,whereas in the persistent mode,plant viruses are retained for a relatively long time and can be found in the hemolymph.Here,we reviewed recent studies that uncovered molecular mechanisms of how plant viruses manipulate host traits for efficient transmission by insect vectors.Normally,plants that are infected with viruses,regardless of the transmission mode,tend to release more attractive volatiles to vectors.However,plant defensive systems are regulated differently by viruses in these three modes.In the non-persistent mode,virus infections significantly induce plant defense responses,which probably trigger vectors(e.g.,winged aphids)to disperse and transmit viruses in a short time.In the semi-persistent mode,virus infections frequently suppress plant defense responses,resulting in an increase of vector population and facilitating viral transmissions during vector outbreaks.In the persistent mode,virus infections reduce plant defense responses and manipulate plant traits to become suitable feeding sites in a relatively long period of time.Understanding the underlying mechanisms of virus–vector–plant interactions will lay a foundation for preventing virus transmission.

HEMIPTERAN-TRANSMITTED PLANT VIRUSES: RESEARCH PROGRESS AND CONTROL STRATEGIES

About 80% of plant viruses are transmitted by specific insect vectors, especiallyhemipterans with piercing-sucking mouthparts. Many virus-transmitting insectsare also important crop pests that cause considerable losses in crop production.This review summarizes the latest research findings on the interactions betweenplant viruses and insect vectors and analyzes the key factors affecting insecttransmission of plant viruses from the perspectives of insect immunity, insectfeeding, and insect symbiotic microorganisms. Additionally, by referring to thelatest applications for blocking the transmission of animal viruses, potentialcontrol strategies to prevent the transmission of insect-vectored plant virusesusing RNAi technology, gene editing technology, and CRISPR/Cas9 + gene-driventechnology are discussed.

Insect transmission of plant viruses： Multilayered interactions optimize viral propagation

By serving as vectors of transmission, insects play a key role in the infection cycle of many plant viruses. Viruses use sophisticated transmission strategies to overcome the spatial barrier separating plants and the impediment imposed by the plant cell wall. Interactions among insect vectors, viruses, and host plants mediate transmission by integrating all organizational levels, from molecules to populations. Best-examined on the molecular scale are two basic transmission modes wherein virus-vector interactions have been well characterized. Whereas association of virus particles with specific sites in the vector＇s mouthparts or in alimentary tract regions immediately posterior to them is required for noncirculative transmission, the cycle of particles through the vector body is necessary for circulative transmission. Virus transmission is also determined by interactions that are associated with changes in vector feeding behaviors and with alterations in plant host＇s morphology and/or metabolism that favor the attraction or deterrence of vectors. A recent concept in virus-host-vector interactions proposes that when vectors land on infected plants, vector elicitors and effectors ＂inform＂ the plants of the confluence of interacting entities and trigger signaling pathways and plant defenses. Simultaneously, the plant responses may also influence virus acquisition and inoculation by vectors. Over- all, a picture is emerging where transmission depends on multilayered virus-vector-host interactions that define the route of a virus through the vector, and on the manipulation of the host and the vector. These interactions guarantee virus propagation until one or more of the interactants undergo changes through evolution or are halted by environmental interventions.

Bioinspired optical antennas: gold plant viruses

The ability to capture the chemical signatures of biomolecules(i.e.,electron-transfer dynamics)in living cells will provide an entirely new perspective on biology and medicine.This can be accomplished using nanoscale optical antennas that can collect,resonate and focus light from outside the cell and emit molecular spectra.Here,we describe biologically inspired nanoscale optical antennas that utilize the unique topologies of plant viruses(and thus,are called gold plant viruses)for molecular fingerprint detection.Our electromagnetic calculations for these gold viruses indicate that capsid morphologies permit high amplification of optical scattering energy compared to a smooth nanosphere.From experimental measurements of various gold viruses based on four different plant viruses,we observe highly enhanced optical cross-sections and the modulation of the resonance wavelength depending on the viral morphology.Additionally,in label-free molecular imaging,we successfully obtain higher sensitivity(by a factor of up to 10^(6))than can be achieved using similar-sized nanospheres.By virtue of the inherent functionalities of capsids and the plasmonic characteristics of the gold layer,a gold virus-based antenna will enable cellular targeting,imaging and drug delivery.

An introductory review on the common brown leafhopper(Orosius orientalis):A new soybean pest

Soybean pests are one of the major factors limiting yield improvement.With the expansion of area and changes in cropping patterns,a number of new pests have been identified in the main soybean production areas of China.The common brown leafhopper,Orosius orientalis,is a new pest associated with soybean stay-green virus that has been discovered on cultivated soybean crop in the Yellow-Huai-hai region of China in recent years.The polyphagous insect has a wide feeding range and infests a variety of important grain and cash crops.This paper presents the basic information,geographical distribution,hosts,damage characteristics,plant virus transmission,occurrence patterns,and prevention and control measures O.orientalis.This review also provides insights into integrated prevention and control of the genus Orosius as an insect vector.

Construction of Plant Virus Expression Vector pClYVV/CP/W and Expression of GFP

[ Objective] The study was to report the construction of plant virus expression vector pCIYVV/CP/W and the expression of green fluorescent protein（GFP） with pCIYVV/CP/W, and to develop effective plat virus vector for plant bioreactor to produce useful protein. [ Method] A section of multiple cloning sites among NIb/CP genes in pCIYVV genome and deoxyribonucleotide polylinker of cleavage recognition sequence containing viral protease Nla were cloned with infectivity full-length cDNA of clover yellow vein virus （CIYVV）, and pCIYVV/CP/W vector was constructed, GFP gene was inserted into pCIyVV/CP/W to construct the pCIYVV/CP/W/GFP vector. The transcription situation of recombinant virus clone was detected by RT-PCR, and targeted gene products expressed by recombinant virus clone were detected with western blot （WB）. [Result] The broad bean seedling inoculated with pCIYVV/CP/W/GFP expressed the same symptom as wild type CIYVV, morbidity was of 100%, the result showed that recombinant virus clone pCIYVV/CP/W/GFP didn＇t suppress, insertion of foreign gene didn＇t destroy the open reading frame of pCIYVV/CP/W. Foreign gene can keep living in F, progeny virus genorne steadily, recombinant virus clone pCIYVV/CP/W/GFP could steadily express GFP in progeny virus at least.[ Conclusion] The useful plant virus vector was provided for useful protein expressing.

Plant virology in the 21st century in China:Recent advances and future directions

Plant viruses are a group of intracellular pathogens that persistently threaten global food security.Significant advances in plant virology have been achieved by Chinese scientists over the last 20 years,including basic research and technologies for preventing and controlling plant viral diseases.Here,we review these milestones and advances,including the identification of new crop-infecting viruses,dissection of pathogenic mechanisms of multiple viruses,examination of multilayered interactions among viruses,their host plants,and virus-transmitting arthropod vectors,and in-depth interrogation of plantencoded resistance and susceptibility determinants.Notably,various plant virus-based vectors have also been successfully developed for gene function studies and target gene expression in plants.We also recommend future plant virology studies in China.

Sugarcane Transcript Profiling Assessed by cDNA-AFLP Analysis during the Interaction with Sugarcane Mosaic Virus

Sugarcane mosaic caused by Sugarcane Mosaic Virus (SCMV) is one of the most important virus diseases of sugarcane. In the present study, changes in the transcription profile obtained by cDNA-AFLP analysis were investigated in two sugarcane varieties contrasting to SCMV resistance, when challenged with a severe virus strain. Healthy plants derived from meristem tip tissue culture were mechanically inoculated under greenhouse controlled conditions and sampled at 24, 48 and 72 hours after inoculation. A total of 392 transcript-derived fragments (TDFs) were verified in the resistant variety against 380 in the susceptible one. The two sugarcane genotypes showed differential behavior in the number of induced and repressed TDFs along the time-course samplings. Ten out of 23 sequenced TDFs (unique from the resistance variety), showed identity with known plant sequences, mostly related to plant defense mechanisms against pathogens. The cDNA-AFLP technique was effective in revealing changes in the transcription profile within and between contrasting varieties when challenged by SCMV.

Phosphoinositides in plant-pathogen interaction:trends and perspectives

Phosphoinositides are important regulatory membrane lipids,with a role in plant development and cellular function.Emerging evidence indicates that phosphoinositides play crucial roles in plant defence and are also utilized by pathogens for infection.In this review,we highlight the role of phosphoinositides in plant-pathogen interaction and the implication of this remarkable convergence in the battle against plant diseases.

Roles of RNA m^(6)A modifications in plant-virus interactions

Viral RNAs have been known to contain N^(6)-methyladenosine(m^(6)A)modifications since the 1970s.The function of these modifications remained unknown until the development of genome-wide methods to map m^(6)A residues.Increasing evidence has recently revealed a strong association between m^(6)A modifications and plant viral infection.This highlight introduces advances in the roles of RNA m^(6)A modifications in plant-virus interactions.

To Gate, or Not to Gate： Regulatory Mechanisms for Intercellular Protein Transport and Virus Movement in Plants

Cell-to-cell signal transduction is vital for orchestrating the whole-body physiology of multi-cellular organ- isms, and many endogenous macromolecules, proteins, and nucleic acids function as such transported signals. In plants, many of these molecules are transported through plasmodesmata （Pd）, the cell wall-spanning channel structures that interconnect plant cells. Furthermore, Pd also act as conduits for cell-to-cell movement of most plant viruses that have evolved to pirate these channels to spread the infection. Pd transport is presumed to be highly selective, and only a limited repertoire of molecules is transported through these channels. Recent studies have begun to unravel mechanisms that actively regulate the opening of the Pd channel to allow traffic. This macromolecular transport between cells comprises two consecutive steps： intracellular targeting to Pd and translocation through the channel to the adjacent cell. Here, we review the current knowledge of molecular species that are transported though Pd and the mechanisms that control this traffic. Generally, Pd traffic can occur by passive diffusion through the trans-Pd cytoplasm or through the membrane/lu- men of the trans-Pd ER, or by active transport that includes protein-protein interactions. It is this latter mode of Pd trans- port that is involved in intercellular traffic of most signal molecules and is regulated by distinct and sometimes interdependent mechanisms, which represent the focus of this article.

Coat protein of Chinese wheat mosaic virus upregulates and interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenase,a negative regulator of plant autophagy,to promote virus infection

Autophagy is an intracellular degradation mechanism involved in antiviral defense,but the strategies employed by plant viruses to counteract autophagy-related defense remain unknown for the majority of the viruses.Herein,we describe how the Chinese wheat mosaic virus(CWMV,genus Furovirus)interferes with autophagy and enhances its infection in Nicotiana benthamiana.Yeast two-hybrid screening and in vivo/in vitro assays revealed that the 19 k Da coat protein(CP19 K)of CWMV interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenases(GAPCs),negative regulators of autophagy,which bind autophagy-related protein 3(ATG3),a key factor in autophagy.CP19 K also directly interacts with ATG3,possibly leading to the formation of a CP19 K–GAPC–ATG3 complex.CP19 K–GAPC interaction appeared to intensify CP19 K–ATG3 binding.Moreover,CP19 K expression upregulated GAPC gene transcripts and reduced autophagic activities.Accordingly,the silencing of GAPC genes in transgenic N.benthamiana reduced CWMV accumulation,whereas CP19 K overexpression enhanced it.Overall,our results suggest that CWMV CP19 K interferes with autophagy through the promotion and utilization of the GAPC role as a negative regulator of autophagy.

Characterization of protein-protein interactions between rice viruses and vector insects

Planthoppers are the most notorious rice pests,because they transmit various rice viruses in a persistent-propagative manner.Protein–protein interactions(PPIs)between virus and vector are crucial for virus transmission by vector insects.However,the number of known PPIs for pairs of rice viruses and planthoppers is restricted by low throughput research methods.In this study,we applied DeNovo,a virus-host sequence-based PPI predictor,to predict potential PPIs at a genome-wide scale between three planthoppers and five rice viruses.PPIs were identified at two different confidence thresholds,referred to as low and high modes.The number of PPIs for the five planthopper-virus pairs ranged from 506 to 1985 in the low mode and from 1254 to 4286 in the high mode.After eliminating the“one-too-many”redundant interacting information,the PPIs with unique planthopper proteins were reduced to 343–724 in the low mode and 758–1671 in the high mode.Homologous analysis showed that 11 sets and 31 sets of homologous planthopper proteins were shared by all planthopper-virus interactions in the two modes,indicating that they are potential conserved vector factors essential for transmission of rice viruses.Ten PPIs between small brown planthopper and rice stripe virus(RSV)were verified using glutathione-S-transferase(GST)/His-pull down or co-immunoprecipitation assay.Five of the ten PPIs were proven positive,and three of the five SBPH proteins were confirmed to interact with RSV.The predicted PPIs provide new clues for further studies of the complicated relationship between rice viruses and their vector insects.

Nucleotide bias of DCL and AGO in plant anti-virus gene silencing

Plant Dicer-like(DCL)and Argonaute(AGO)are the key enzymes involved in anti-virus post-transcriptional gene silencing(AV-PTGS).Here we show that AV-PTGS exhibited nucleotide preference by calculating a relative AV-PTGS efficiency on processing viral RNA substrates.In comparison with genome sequences of dicot-infecting Turnip mosaic virus(TuMV)and monocot-infecting Cocksfoot streak virus(CSV),viral-derived small interfering RNAs(vsiRNAs)displayed positive correlations between AV-PTGS efficiency and G+C content(GC%).Further investigations on nucleotide contents revealed that the vsiRNA populations had G-biases.This finding was further supported by our analyses of previously reported vsiRNA populations in diverse plant-virus associations,and AGO associated Arabidopsis endogenous siRNA populations,indicating that plant AGOs operated with G-preference.We further propose a hypothesis that AV-PTGS imposes selection pressure(s)on the evolution of plant viruses.This hypothesis was supported when potyvirus genomes were analysed for evidence of GC elimination,suggesting that plant virus evolution to have low GC%genomes would have a unique function,which is to reduce the host AV-PTGS attack during infections.

Modeling the effects of cross-protection control in plant disease with seasonality

Cross-protection in plants has been widely used to control losses caused by virus diseases in the world. Here, a non-autonomous plant-virus disease model was developed includ- ing cross-protection. Global dynamics of the model was discussed. Under the quite weak assumptions, integral form conditions were resolved for permanence of the system and extinction of diseases. Furthermore, we looked into the sufficient conditions that plants could be protected against the detrimental effects of infection by an infection with the mild virus isolates. Last, we performed numerical simulations. Our investigations sug- gested that cross-protection played an important role in controlling the spread of the challenging virus in plants.

Perspectives on plant virus diseases in a climate change scenario of elevated temperatures

Global food production is at risk from many abiotic and biotic stresses and can be affected by multiple stresses simultaneously.Virus diseases damage cultivated plants and decrease the marketable quality of produce.Importantly,the progression of virus diseases is strongly affected by changing climate conditions.Among climate-changing vari-ables,temperature increase is viewed as an important factor that affects virus epidemics,which may in turn require more efficient disease management.In this review,we discuss the effect of elevated temperature on virus epidem-ics at both macro-and micro-climatic levels.This includes the temperature effects on virus spread both within and between host plants.Furthermore,we focus on the involvement of molecular mechanisms associated with tempera-ture effects on plant defence to viruses in both susceptible and resistant plants.Considering various mechanisms proposed in different pathosystems,we also offer a view of the possible opportunities provided by RNA-based technologies for virus control at elevated temperatures.Recently,the potential of these technologies for topical field applications has been strengthened through a combination of genetically modified(GM)-free delivery nanoplat-forms.This approach represents a promising and important climate-resilient substitute to conventional strategies for managing plant virus diseases under global warming scenarios.In this context,we discuss the knowledge gaps in the research of temperature effects on plant-virus interactions and limitations of RNA-based emerging technologies,which should be addressed in future studies.

Rice yellow stunt virus activates polyamine biosynthesis to promote viral propagation in insect vectors by disrupting ornithine decarboxylase antienzyme function

Intracellular polyamines(putrescine,spermidine,and spermine)have emerged as important molecules for viral infection;however,how viruses activate polyamines biosynthesis to promote viral infection remains unclear.Ornithine decarboxylase 1(ODC1)and its antienzyme 1(OAZ1)are major regulators of polyamine biosynthesis in animal cells.Here,we report that rice yellow stunt virus(RYSV),a plant rhabdovirus,could activate putrescine biosynthesis in leafhoppers to promote viral propagation by inhibiting OAZ1 expression.We observed that the reduction of putrescine biosynthesis by treatment with difluormethylornithine(DFMO),a specific nontoxic inhibitor of ODC1,or with in vitro synthesized dsRNAs targeting ODC1 mRNA could inhibit viral infection.In contrast,the supplement of putrescine or the increase of putrescine biosynthesis by treatment with ds RNAs targeting OAZ1 mRNA could facilitate viral infection.We further determined that both RYSV matrix protein M and ODC1 directly bind to the ODC-binding domain at the C-terminus of OAZ1.Thus,viral propagation in leafhoppers would decrease the ability of OAZ1 to target and mediate the degradation of ODC1,which finally activates putrescine production to benefit viral propagation.This work reveals that polyamine-metabolizing enzymes are directly exploited by a vector-borne virus to increase polyamine production,thereby facilitating viral infection in insect vectors.

A DNA-Binding Bromodomain-Containing Protein Interacts with and Reduces Rx1-Mediated Immune Response to Potato Virus X

Plant NLR proteins enable the immune systemto recognize and respond to pathogen attack.An early consequence of immune activation is transcriptional reprogramming.SomeNLRs have been shownto act in the nucleus and interact with transcription factors.The Rx1 NLR protein of potato binds and distorts doublestranded DNA.However,the components of the chromatin-localized Rx1 complex are largely unknown.Here,we report a physical and functional interaction between Rx1 and NbDBCP,a bromodomaincontaining chromatin-interacting protein.NbDBCP accumulates in the nucleoplasmand nucleolus,interacts with chromatin,and redistributes Rx1 tothe nucleolus in a subpopulation of imaged cells.Rx1 overexpression reduces the interaction between NbDBCP and chromatin.NbDBCP is a negative regulator of Rx1-mediated immune responses to potato virus X(PVX),and this activity requires an intact bromodomain.Previously,Rx1 has been shown to regulate the DNA-binding activity of a Golden2-like transcription factor,NbGlk1.Rx1 and NbDBCP act synergistically to reduce NbGlk1 DNA binding,suggesting a mode of action for NbDBCP’s inhibitory effect on immunity.This study provides new mechanistic insight into the mechanism by which a chromatin-localized NLR complex co-ordinates immune signaling after pathogen perception.