Plant Virus-Insect Vector Interactions: Current and Potential Future Research Directions

Densovirus infection facilitates plant-virus transmission by an aphid

The interactions among plant viruses, insect vectors, and host plants have been well studied; however, the roles of insect viruses in this system have largely been neglected. We investigated the effects of MpnDV infection on aphid and PVY transmission using bioassays, RNA interference (RNAi), and GC-MS methods and green peach aphid (Myzus persicae (Sulzer)), potato virus Y (PVY), and densovirus (Myzus persicae nicotianae densovirus, MpnDV) as model systems. MpnDV increased the activities of its host, promoting population dispersal and leading to significant proliferation in tobacco plants by significantly enhancing the titer of the sesquiterpene (E)-β-farnesene (EβF) via up-regulation of expression levels of the MpFPPS1 gene. The proliferation and dispersal of MpnDV-positive individuals were faster than that of MpnDV-negative individuals in PVY-infected tobacco plants, which promoted the transmission of PVY. These results combined showed that an insect virus may facilitate the transmission of a plant virus by enhancing the locomotor activity and population proliferation of insect vectors. These findings provide novel opportunities for controlling insect vectors and plant viruses, which can be used in the development of novel management strategies.

Genetic variations and gene expression profiles of Rice Black-streaked dwarf virus (RBSDV) in different host plants and insect vectors: insights from RNA-Seq analysis

Rice black-streaked dwarf virus (RBSDV) is an etiological agent of a destructive disease infecting some economically important crops from the Gramineae family in Asia. While RBSDV causes high yield losses, genetic characteristics of replicative viral populations have not been investigated within different host plants and insect vectors. Herein, eleven publicly available RNA-Seq datasets from Chinese RBSDV-infected rice, maize, and viruliferous planthopper (Laodelphax striatellus) were obtained from the NCBI database. The patterns of SNP and RNA expression profiles of expected RBSDV populations were analyzed by CLC Workbench 20 and Geneious Prime software. These analyses discovered 2,646 mutations with codon changes in RBSDV whole transcriptome and forty-seven co-mutated hotspots with high variant frequency within the crucial regions of S5-1, S5-2, S6, S7-1, S7-2, S9, and S10 open reading frames (ORFs) which are responsible for some virulence and host range functions. Moreover, three joint mutations are located on the three-dimensional protein of P9-1. The infected RBSDV-susceptible rice cultivar KTWYJ3 and indigenous planthopper datasets showed more co-mutated hotspot numbers than others. Our analyses showed the expression patterns of viral genomic fragments varied depending on the host type. Unlike planthopper, S5-1, S2, S6, and S9-1 ORFs, respectively had the greatest read numbers in host plants; and S5-2, S9-2, and S7-2 were expressed in the lowest level. These findings underscore virus/host complexes are effective in the genetic variations and gene expression profiles of plant viruses. Our analysis revealed no evidence of recombination events. Interestingly, the negative selection was observed at 12 RBSDV ORFs, except for position 1015 in the P1 protein, where a positive selection was detected. The research highlights the potential of SRA datasets for analysis of the virus cycle and enhances our understanding of RBSDV's genetic diversity and host specificity.

Helper Component-Proteinase of Triticum Mosaic Virus Is a Viral Determinant of Wheat Curl Mite Transmission

Triticum mosaic virus (TriMV; genus Poacevirus; family Potyviridae) is an economically important virus in the Great Plains region of the United States. TriMV is transmitted by the wheat curl mite (Aceria tosichella) Type 2 genotype but not by Type 1. Helper component-proteinase (HC-Pro) is a vector transmission determinant for several potyvirids, but the role of HC-Pro in TriMV transmission is unknown. In this study, we examined the requirement of the HC-Pro cistron of TriMV for wheat curl mite (Type 2) transmission through deletion and point mutations and constructing TriMV chimeras with heterologous HC-Pros from other potyvirids. TriMV with complete deletion of HC-Pro failed to be transmitted by wheat curl mites at detectable levels. Furthermore, TriMV chimeras with heterologous HC-Pros from aphid-transmitted turnip mosaic virus and tobacco etch virus, or wheat curl mite-transmitted wheat streak mosaic virus, failed to be transmitted by wheat curl mites. These data suggest that heterologous HC-Pros did not complement TriMV for wheat curl mite transmission. A decreasing series of progressive nested in-frame deletions at the N-terminal region of HC-Pro comprising amino acids 3 to 125, 3 to 50, 3 to 25, 3 to 15, 3 to 8, and 3 and 4 abolished TriMV transmission by wheat curl mites. Additionally, mutation of conserved His20, Cys49, or Cys52 to Ala in HC-Pro abolished TriMV transmissibility by wheat curl mites. These data suggest that the N-terminal region of HC-Pro is crucial for TriMV transmission by wheat curl mites. Collectively, these data demonstrate that the HC-Pro cistron of TriMV is a viral determinant for wheat curl mite transmission.

Aphidius colemani Behavior Changes Depending on Volatile Organic Compounds Emitted by Plants Infected with Viruses with Different Modes of Transmission

Natural enemies are an additional component that may interact directly with the plant-virus-vector association, affecting viral dispersion. In our study, we conducted olfactometry assays to explore how single and mixed infections with CMV or/and CABYV modify the attractiveness of A. colemani to aphid-free and aphid-infested melon plants using two melon genotypes. Subsequently, we investigated the influence of CABYV-infected plants infested by A. gossypii on the parasitism rate and emergence of A. colemani in a dual-choice assay under greenhouse conditions. Our study demonstrates that males showed no preference for either infected or non-infected plants. Female parasitoids exhibit a preference for volatiles emitted by CMV and mixed-infected melon plants over clean air but not over mock-inoculated plants, suggesting a response influenced by plant genotype. Female parasitoid responses to CABYV and its interactions with aphids revealed a preference for mock-inoculated plants over CABYV-infected plants and a parasitism rate slightly higher (7.12%) on non-infected plants. Our study revealed that (1) parasitoids may reject olfactory cues from CABYV-infected plants, potentially interfering with the plant's "cry for help" response; (2) in the case of CMV, whether in single or mixed infections, non-infected plants are as attractive as infected ones to parasitoids. Our findings suggest that persistent viruses manipulate aphid parasitoid behavior to their advantage, promoting virus disease in melon crops.

New Insights into Hop Latent Viroid Detection, Infectivity, Host Range, and Transmission

Hop latent viroid (HLVd), a subviral pathogen from the family Pospiviroidae, is a major threat to the global cannabis industry and is the causative agent for "dudding disease". Infected plants can often be asymptomatic for a period of growth and then develop symptoms such as malformed and yellowing leaves, as well as stunted growth. During flowering, HLVd-infected plants show reduced levels of valuable metabolites. This study was undertaken to expand our basic knowledge of HLVd infectivity, transmission, and host range. HLVd-specific primers were used for RT-PCR detection in plant samples and were able to detect HLVd in as little as 5 picograms of total RNA. A survey of hemp samples obtained from a diseased production system proved sole infection of HLVd (72%) with no coexistence of hop stunt viroid. HLVd was infectious through successive passage assays using a crude sap or total RNA extract derived from infected hemp. HLVd was also highly transmissible through hemp seeds at rates of 58 to 80%. Host range assays revealed new hosts for HLVd: tomato, cucumber, chrysanthemum, Nicotiana benthamiana, and Arabidopsis thaliana (Col-0). Sequence analysis of 77 isolates revealed only 3 parsimony-informative sites, while 10 sites were detected among all HLVd isolates available in the GenBank. The phylogenetic relationship among HLVd isolates allowed for inferring two major clades based on the genetic distance. Our findings facilitate further studies on host-viroid interaction and viroid management.

The essential role of clathrin-mediated endocytosis and early endosomes in the trafficking of begomoviruses through the primary salivary glands of their whitefly vectors

IMPORTANCE

Many plant viruses are transmitted by insect vectors in a circulative manner. For efficient transmission, the entry of the virus from vector hemolymph into the primary salivary gland (PSG) is a step of paramount importance. Yet, vector components mediating virus entry into PSG remain barely characterized. Here, we demonstrate the role of clathrin-mediated endocytosis and early endosomes in begomovirus entry into whitefly PSG. Our findings unravel the key components involved in begomovirus transport within the whitefly body and transmission by their whitefly vectors and provide novel clues for blocking begomovirus transmission.

An Observation of a Very High Swelling of Bromovirus Members at Specific Ionic Strengths and pH

Cowpea chlorotic mottle virus (CCMV) and brome mosaic virus (BMV) are naked plant viruses with similar characteristics; both form a T = 3 icosahedral protein capsid and are members of the bromoviridae family. It is well known that these viruses completely disassemble and liberate their genome at a pH around 7.2 and 1 M ionic strength. However, the 1 M ionic strength condition is not present inside cells, so an important question is how these viruses deliver their genome inside cells for their viral replication. There are some studies reporting the swelling of the CCMV virus using different techniques. For example, it is reported that at a pH~7.2 and low ionic strength, the swelling observed is about 10% of the initial diameter of the virus. Furthermore, different regions within the cell are known to have different pH levels and ionic strengths. In this work, we performed several experiments at low ionic strengths of 0.1, 0.2, and 0.3 and systematically increased the pH in 0.2 increments from 4.6 to 7.4. To determine the change in virus size at the different pHs and ionic strengths, we first used dynamic light scattering (DLS). Most of the experiments agree with a 10% capsid swelling under the conditions reported in previous works, but surprisingly, we found that at some particular conditions, the virus capsid swelling could be as big as 20 to 35% of the original size. These measurements were corroborated by atomic force microscopy (AFM) and transmission electron microscopy (TEM) around the conditions where the big swelling was determined by DLS. Therefore, this big swelling could be an easier mechanism that viruses use inside the cell to deliver their genome to the cell machinery for viral replication.

A systematic review of southern rice black-streaked dwarf virus in the age of omics

Southern rice black-streaked dwarf virus (SRBSDV) is one of the most damaging rice viruses. The virus decreases rice quality and yield, and poses a serious threat to food security. From this perspective, this review performed a survey of published studies in recent years to understand the current status of SRBSDV and white-backed planthopper (WBPH, Sogatella furcifera) transmission processes in rice. Recent studies have shown that the interactions between viral virulence proteins and rice susceptibility factors shape the transmission of SRBSDV. Moreover, the transmission of SRBSDV is influenced by the interactions between viral virulence proteins and S. furcifera susceptibility factors. This review focused on the molecular mechanisms of key genes or proteins associated with SRBSDV infection in rice via the S. furcifera vector, and the host defense response mechanisms against viral infection. A sustainable control strategy using RNAi was summarized to address this pest. Finally, we also present a model for screening anti-SRBSDV inhibitors using viral proteins as targets. © 2023 Society of Chemical Industry.

A Systematic Review on the Viruses of Anopheles Mosquitoes: The Potential Importance for Public Health

Anopheles mosquitoes are the vectors of Plasmodium, the etiological agent of malaria. In addition, Anopheles funestus and Anopheles gambiae are the main vectors of the O'nyong-nyong virus. However, research on the viruses carried by Anopheles is scarce; thus, the possible transmission of viruses by Anopheles is still unexplored. This systematic review was carried out to identify studies that report viruses in natural populations of Anopheles or virus infection and transmission in laboratory-reared mosquitoes. The databases reviewed were EBSCO-Host, Google Scholar, Science Direct, Scopus and PubMed. After the identification and screening of candidate articles, a total of 203 original studies were included that reported on a variety of viruses detected in Anopheles natural populations. In total, 161 viruses in 54 species from 41 countries worldwide were registered. In laboratory studies, 28 viruses in 15 Anopheles species were evaluated for mosquito viral transmission capacity or viral infection. The viruses reported in Anopheles encompassed 25 viral families and included arboviruses, probable arboviruses and Insect-Specific Viruses (ISVs). Insights after performing this review include the need for (1) a better understanding of Anopheles-viral interactions, (2) characterizing the Anopheles virome-considering the public health importance of the viruses potentially transmitted by Anopheles and the significance of finding viruses with biological control activity-and (3) performing virological surveillance in natural populations of Anopheles, especially in the current context of environmental modifications that may potentiate the expansion of the Anopheles species distribution.

Plant and insect virus-like particles: emerging nanoparticles for agricultural pest management

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

An Aphid-Transmitted Virus Reduces the Host Plant Response to Its Vector to Promote Its Transmission

The success of virus transmission by vectors relies on intricate trophic interactions between three partners, the host plant, the virus, and the vector. Despite numerous studies that showed the capacity of plant viruses to manipulate their host plant to their benefit, and potentially of their transmission, the molecular mechanisms sustaining this phenomenon has not yet been extensively analyzed at the molecular level. In this study, we focused on the deregulations induced in Arabidopsis thaliana by an aphid vector that were alleviated when the plants were infected with turnip yellows virus (TuYV), a polerovirus strictly transmitted by aphids in a circulative and nonpropagative mode. By setting up an experimental design mimicking the natural conditions of virus transmission, we analyzed the deregulations in plants infected with TuYV and infested with aphids by a dual transcriptomic and metabolomic approach. We observed that the virus infection alleviated most of the gene deregulations induced by the aphids in a noninfected plant at both time points analyzed (6 and 72 h) with a more pronounced effect at the later time point of infestation. The metabolic composition of the infected and infested plants was altered in a way that could be beneficial for the vector and the virus transmission. Importantly, these substantial modifications observed in infected and infested plants correlated with a higher TuYV transmission efficiency. This study revealed the capacity of TuYV to alter the plant nutritive content and the defense reaction against the aphid vector to promote the viral transmission.

Effects of Host Plants and Their Infection Status on Acquisition and Inoculation of A Plant Virus by Its Hemipteran Vector

Whitefly, Bemisia tabaci Gennadius (B cryptic species), transmits cucurbit leaf crumple virus (CuLCrV) in a persistent fashion. CuLCrV affects several crops such as squash and snap bean in the southeastern United States. CuLCrV is often found as a mixed infection with whitefly transmitted criniviruses, such as cucurbit yellow stunting disorder virus (CYSDV) in hosts such as squash, or as a single infection in hosts such as snap bean. The implications of different host plants (inoculum sources) with varying infection status on CuLCrV transmission/epidemics is not clear. This study conducted a series of whitefly mediated CuLCrV transmission experiments. In the first experiment, three plants species: squash, snap bean, and tobacco were inoculated by whiteflies feeding on field-collected mixed-infected squash plants. In the second experiment, three plant species, namely squash, snap bean, and tobacco with varying infection status (squash infected with CuLCrV and CYSDV and snap bean and tobacco infected with CuLCrV), were used as inoculum sources. In the third experiment, squash plants with differential CuLCrV accumulation levels and infection status (either singly infected with CuLCrV or mixed infected with CuLCrV and CYSDV) were used as inoculum sources. Irrespective of plant species and its infection status, CuLCrV accumulation in whiteflies was dependent upon the CuLCrV accumulation in the inoculum source plants. Furthermore, differential CuLCrV accumulation in whiteflies resulted in differential transmission, CuLCrV accumulation, and disease phenotype in the recipient squash plants. Overall, results demonstrate that whitefly mediated CuLCrV transmission between host plants follows a virus density dependent phenomenon with implications for epidemics.

Transcriptomic and Proteomic Analyses of Myzus persicae Carrying Brassica Yellows Virus

Viruses in the genus Polerovirus infect a wide range of crop plants and cause severe economic crop losses. BrYV belongs to the genus Polerovirus and is transmitted by Myzus persicae. However, the changes in transcriptome and proteome profiles of M. persicae during viral infection are unclear. Here, RNA-Seq and TMT-based quantitative proteomic analysis were performed to compare the differences between viruliferous and nonviruliferous aphids. In total, 1266 DEGs were identified at the level of transcription with 980 DEGs being upregulated and 286 downregulated in viruliferous aphids. At the protein level, among the 18 DEPs identified, the number of upregulated proteins in viruliferous aphids was twice that of the downregulated DEPs. Enrichment analysis indicated that these DEGs and DEPs were mainly involved in epidermal protein synthesis, phosphorylation, and various metabolic processes. Interestingly, the expressions of a number of cuticle proteins and tubulins were upregulated in viruliferous aphids. Taken together, our study revealed the complex regulatory network between BrYV and its vector M. persicae from the perspective of omics. These findings should be of great benefit to screening key factors involved in the process of virus circulation in aphids and provide new insights for BrYV prevention via vector control in the field.

The tracheal immune system of insects - A blueprint for understanding epithelial immunity

The unique design of respiratory organs in multicellular organisms makes them prone to infection by pathogens. To cope with this vulnerability, highly effective local immune systems evolved that are also operative in the tracheal system of insects. Many pathogens and parasites (including viruses, bacteria, fungi, and metazoan parasites) colonize the trachea or invade the host via this route. Currently, only two modules of the tracheal immune system have been characterized in depth: 1) Immune deficiency pathway-mediated activation of antimicrobial peptide gene expression and 2) local melanization processes that protect the structure from wounding. There is an urgent need to increase our understanding of the architecture of tracheal immune systems, especially regarding those mechanisms that enable the maintenance of immune homeostasis. This need for new studies is particularly exigent for species other than Drosophila.

Diversity and phylogeography of begomoviruses and DNA satellites associated with the leaf curl and mosaic disease complex of eggplant

Eggplant is one of the important vegetable crops grown across the world, and its production is threatened by both biotic and abiotic stresses. Diseases caused by viruses are becoming major limiting factors for its successful cultivation. A survey for begomovirus-like symptoms in 72 eggplant fields located in six different Indian states revealed a prevalence of disease ranging from 5.2 to 40.2%, and the symptoms recorded were mosaic, mottling, petiole bending, yellowing, and upward curling, vein thickening, and enation of the leaves, and stunting of plants. The causal agent associated with these plants was transmitted from infected leaf samples to healthy eggplant seedlings via grafting and whiteflies (Bemisia tabaci). The presence of begomovirus was confirmed in 72 infected eggplant samples collected from the surveyed fields exhibiting leaf curl and mosaic disease by PCR using begomovirus specifc primers (DNA-A componet), which resulted in an expected amplicon of 1.2 kb. The partial genome sequence obtained from amplified 1.2 kb from all samples indicated that they are closely related begomovirus species, tomato leaf Karnataka virus (ToLCKV, two samples), tomato leaf curl Palampur virus (ToLCPalV, fifty eggplant samples), and chilli leaf curl virus (ChLCuV, twenty samples). Based on the partial genome sequence analysis, fourteen representative samples were selected for full viral genome amplification by the rolling circle DNA amplification (RCA) technique. Analyses of fourteen eggplant isolates genome sequences using the Sequence Demarcation Tool (SDT) indicated that one isolate had the maximum nucleotide (nt) identity with ToLCKV and eight isolates with ToLCPalV. Whereas, four isolates four isolates (BLC1-CH, BLC2-CH, BLC3-CH, BLC4-CH) are showing nucleotide identity of less than 91% with chilli infecting viruses begomoviruses with chilli infecting begomoviruses and as per the guidelines given by the ICTV study group for the classification of begomoviruses these isolates are considered as one novel begomovirus species, for which name, Eggplant leaf curl Chhattisgarh virus (EgLCuChV) is proposed. For DNA-B component, seven eggplant isolates had the highest nt identity with ToLCPalV infecting other crops. Further, DNA satellites sequence analysis indicated that four betasatellites identified shared maximum nucleotide identity with the tomato leaf curl betasatellite and five alphasatellites shared maximum nucleotide identity with the ageratum enation alphasatellite. Recombination and GC plot analyses indicated that the bulk of begomovirus genome and associated satellites presumably originated from of previously known mono and bipartite begomoviruses and DNA satellites. To the best of our knowledge, this is India's first report of ToLCKV and a noval virus, eggplant leaf curl Chhattisgarh virus associated with eggplant leaf curl disease.

Novel Putative Tymoviridae-like Virus Isolated from Culex Mosquitoes in Colombia

The family Tymoviridae comprises positive-sense RNA viruses, which mainly infect plants. Recently, a few Tymoviridae-like viruses have been found in mosquitoes, which feed on vertebrate sources. We describe a novel Tymoviridae-like virus, putatively named, Guachaca virus (GUAV), isolated from Culex pipiens and Culex quinquefasciatus species of mosquitoes and collected in the rural area of Santa Marta, Colombia. After a cytopathic effect was observed in C6/36 cells, RNA was extracted and processed through the NetoVIR next-generation sequencing protocol, and data were analyzed through the VirMAP pipeline. Molecular and phenotypic characterization of the GUAV was achieved using a 5'/3' RACE, transmission electron microscopy, amplification in vertebrate cells, and phylogenetic analysis. A cytopathic effect was observed in C6/36 cells three days post-infection. The GUAV genome was successfully assembled, and its polyadenylated 3' end was corroborated. GUAV shared only 54.9% amino acid identity with its closest relative, Ek Balam virus, and was grouped with the latter and other unclassified insect-associated tymoviruses in a phylogenetic analysis. GUAV is a new member of a family previously described as comprising plant-infecting viruses, which seem to infect and replicate in mosquitoes. The sugar- and blood-feeding behavior of the Culex spp., implies a sustained contact with plants and vertebrates and justifies further studies to unravel the ecological scenario for transmission.

Population genetics and phylogeography of alfalfa mosaic virus in China and a comparison with other regional epidemics based on the cp gene

Alfalfa mosaic virus (AMV) is the most pervasive epidemic virus affecting alfalfa production. However, detailed investigations on the molecular population genetics and evolutionary dynamics of AMV are scarce. This study aimed to report on a large-scale long-term survey of genetic variability in AMV populations from China and perform a comparative analysis of AMV population genetics in the three most thoroughly studied countries to date: China, Iran, and Spain. The study was based on the analysis of the coat protein gene (cp) using two analytical approaches: an analysis of molecular variance (AMOVA) and a Bayesian Markov Chain Monte Carlo approach that investigates the association between geographical origin and phylogeny. Both analytical approaches found significant genetic differentiation within localities, but not among localities nor among provinces. This observation might result from inappropriate agronomical practices involving extensive exchange of plant materials followed by rapid viral diversification within localities. In the Chinese population, both methods found that genetic diversification in AMV was strongly associated with different bioclimatic zones. Rates of molecular evolution were similar in the three countries. The estimated epidemic exponential population size and growth rate suggest that the epidemics grew faster and with higher incidence in Iran, followed by Spain and China. Estimates of the time to the most recent common ancestors suggest that AMV was first seen in Spain by the beginning of the twentieth century and later on in eastern and central Eurasia. After ruling out the existence of recombination breakpoints within the cp gene, a codon-based selection analysis per population was performed and identified many codons under significant negative selection and a few under significant positive selection; the latter varied among countries, suggesting regional differences in selective pressures.

Discovery of novel whitefly vector proteins that interact with a virus capsid component mediating virion retention and transmission

Specificity and efficiency of plant virus transmission depend largely on protein-protein interactions of vectors and viruses. Cucurbit chlorotic yellows virus (CCYV), transmitted specifically by tobacco whitefly, Bemisia tabaci, in a semi-persistent manner, has caused serious damage on cucurbit and vegetable crops around the world. However, the molecular mechanism of interaction during CCYV retention and transmission are still lacking. CCYV was proven to bind particularly to the whitefly foregut, and here, we confirmed that the minor coat protein (CPm) of CCYV is participated in the interaction with the vector. In order to identify proteins of B. tabaci that interact directly with CPm of CCYV, the immunoprecipitation (IP) assay and DUALmembrane cDNA library screening technology were applied. The cytochrome c oxidase subunit 5A (COX), tubulin beta chain (TUB) and keratin, type I cytoskeletal 9-like (KRT) of B. tabaci shown strong interactions with CPm and are closely associated with the retention within the vector and transmission of CCYV. These findings on whitefly protein-CCYV CPm interactions are crucial for a much better understanding the mechanism of semi-persistent plant virus transmission by insect vectors, as well as for implement new strategies for effective management of plant viruses and their vector insects.

Sugarcane multitrophic interactions: Integrating belowground and aboveground organisms

Sugarcane is a crop of major importance used mainly for sugar and biofuel production, and many additional applications of its byproducts are being developed. Sugarcane cultivation is plagued by many insect pests and pathogens that reduce sugarcane yields overall. Recently emerging studies have shown complex multitrophic interactions in cultivated areas, such as the induction of sugarcane defense-related proteins by insect herbivory that function against fungal pathogens that commonly appear after mechanical damage. Fungi and viruses infecting sugarcane also modulate insect behavior, for example, by causing changes in volatile compounds responsible for insect attraction or repelling natural vector enemies via a mechanism that increases pathogen dissemination from infected plants to healthy ones. Interestingly, the fungus Fusarium verticillioides is capable of being vertically transmitted to insect offspring, ensuring its persistence in the field. Understanding multitrophic complexes is important to develop better strategies for controlling pathosystems affecting sugarcane and other important crops and highlights the importance of not only studying binary interactions but also adding as many variables as possible to effectively translate laboratory research to real-life conditions.

Vector acquisition and co-inoculation of two plant viruses influences transmission, infection, and replication in new hosts

This study investigated the role of vector acquisition and transmission on the propagation of single and co-infections of tomato yellow leaf curl virus (TYLCV,) and tomato mottle virus (ToMoV) (Family: Geminiviridae, Genus: Begomovirus) by the whitefly vector Bemisia tabaci MEAM1 (Gennadius) in tomato. The aim of this research was to determine if the manner in which viruses are co-acquired and co-transmitted changes the probability of acquisition, transmission and new host infections. Whiteflies acquired virus by feeding on singly infected plants, co-infected plants, or by sequential feeding on singly infected plants. Viral titers were also quantified by qPCR in vector cohorts, in artificial diet, and plants after exposure to viruliferous vectors. Differences in transmission, infection status of plants, and titers of TYLCV and ToMoV were observed among treatments. All vector cohorts acquired both viruses, but co-acquisition/co-inoculation generally reduced transmission of both viruses as single and mixed infections. Co-inoculation of viruses by the vector also altered virus accumulation in plants regardless of whether one or both viruses were propagated in new hosts. These findings highlight the complex nature of vector-virus-plant interactions that influence the spread and replication of viruses as single and co-infections.

Insight into aphid mediated Potato Virus Y transmission: A molecular to bioinformatics prospective

Potato, the world's most popular crop is reported to provide a food source for nearly a billion people. It is prone to a number of biotic stressors that affect yield and quality, out of which Potato Virus Y (PVY) occupies the top position. PVY can be transmitted mechanically and by sap-feeding aphid vectors. The application of insecticide causes an increase in the resistant vector population along with detrimental effects on the environment; genetic resistance and vector-virus control are the two core components for controlling the deadly PVY. Using transcriptomic tools together with differential gene expression and gene discovery, several loci and genes associated with PVY resistance have been widely identified. To combat this virus we must increase our understanding on the molecular response of the PVY-potato plant-aphid interaction and knowledge of genome organization, as well as the function of PVY encoded proteins, genetic diversity, the molecular aspects of PVY transmission by aphids, and transcriptome profiling of PVY infected potato cultivars. Techniques such as molecular and bioinformatics tools can identify and monitor virus transmission. Several studies have been conducted to understand the molecular basis of PVY resistance/susceptibility interactions and their impact on PVY epidemiology by studying the interrelationship between the virus, its vector, and the host plant. This review presents current knowledge of PVY transmission, epidemiology, genome organization, molecular to bioinformatics responses, and its effective management.

Maize Lethal Necrosis disease: review of molecular and genetic resistance mechanisms, socio-economic impacts, and mitigation strategies in sub-Saharan Africa

BACKGROUND

Maize lethal necrosis (MLN) disease is a significant constraint for maize producers in sub-Saharan Africa (SSA). The disease decimates the maize crop, in some cases, causing total crop failure with far-reaching impacts on regional food security.

RESULTS

In this review, we analyze the impacts of MLN in Africa, finding that resource-poor farmers and consumers are the most vulnerable populations. We examine the molecular mechanism of MLN virus transmission, role of vectors and host plant resistance identifying a range of potential opportunities for genetic and phytosanitary interventions to control MLN. We discuss the likely exacerbating effects of climate change on the MLN menace and describe a sobering example of negative genetic association between tolerance to heat/drought and susceptibility to viral infection. We also review role of microRNAs in host plant response to MLN causing viruses as well as heat/drought stress that can be carefully engineered to develop resistant varieties using novel molecular techniques.

CONCLUSIONS

With the dual drivers of increased crop loss due to MLN and increased demand of maize for food, the development and deployment of simple and safe technologies, like resistant cultivars developed through accelerated breeding or emerging gene editing technologies, will have substantial positive impact on livelihoods in the region. We have summarized the available genetic resources and identified a few large-effect QTLs that can be further exploited to accelerate conversion of existing farmer-preferred varieties into resistant cultivars.

Cotton leaf curl Multan virus differentially regulates innate antiviral immunity of whitefly (Bemisia tabaci) vector to promote cryptic species-dependent virus acquisition

Begomoviruses represent the largest group of economically important, highly pathogenic, DNA plant viruses that contribute a substantial amount of global crop disease burden. The exclusive transmission of begomoviruses by whiteflies (Bemisia tabaci) requires them to interact and efficiently manipulate host responses at physiological, biological and molecular scales. However, the molecular mechanisms underlying complex begomovirus-whitefly interactions that consequently substantiate efficient virus transmission largely remain unknown. Previously, we found that whitefly Asia II 7 cryptic species can efficiently transmit cotton leaf curl Multan virus (CLCuMuV) while MEAM1 cryptic species is a poor carrier and incompetent vector of CLCuMuV. To investigate the potential mechanism/s that facilitate the higher acquisition of CLCuMuV by its whitefly vector (Asia II 7) and to identify novel whitefly proteins that putatively interact with CLCuMuV-AV1 (coat protein), we employed yeast two-hybrid system, bioinformatics, bimolecular fluorescence complementation, RNA interference, RT-qPCR and bioassays. We identified a total of 21 Asia II 7 proteins putatively interacting with CLCuMuV-AV1. Further analyses by molecular docking, Y2H and BiFC experiments validated the interaction between a whitefly innate immunity-related protein (BTB/POZ) and viral AV1 (coat protein). Gene transcription analysis showed that the viral infection significantly suppressed the transcription of BTB/POZ and enhanced the accumulation of CLCuMuV in Asia II 7, but not in MEAM1 cryptic species. In contrast to MEAM1, the targeted knock-down of BTB/POZ substantially reduced the ability of Asia II 7 to acquire and accumulate CLCuMuV. Additionally, antiviral immune signaling pathways (Toll, Imd, Jnk and Jak/STAT) were significantly suppressed following viral infection of Asia II 7 whiteflies. Taken together, the begomovirus CLCuMuV potentiates efficient virus accumulation in its vector B. tabaci Asia II 7 by targeting and suppressing the transcription of an innate immunity-related BTB/POZ gene and other antiviral immune responses in a cryptic species-specific manner.

Nontoxic and Naturally Occurring Active Compounds as Potential Inhibitors of Biological Targets in Liriomyza trifolii

In recent years, novel strategies to control insects have been based on protease inhibitors (PIs). In this regard, molecular docking and molecular dynamics simulations have been extensively used to investigate insect gut proteases and the interactions of PIs for the development of resistance against insects. We, herein, report an in silico study of (disodium 5'-inosinate and petunidin 3-glucoside), (calcium 5'-guanylate and chlorogenic acid), chlorogenic acid alone, (kaempferol-3,7-di-O-glucoside with hyperoside and delphinidin 3-glucoside), and (myricetin 3'-glucoside and hyperoside) as potential inhibitors of acetylcholinesterase receptors, actin, α-tubulin, arginine kinase, and histone receptor III subtypes, respectively. The study demonstrated that the inhibitors are capable of forming stable complexes with the corresponding proteins while also showing great potential for inhibitory activity in the proposed protein-inhibitor combinations.

A Numerical Study of the Dynamics of Vector-Born Viral Plant Disorders Using a Hybrid Artificial Neural Network Approach

Most plant viral infections are vector-borne. There is a latent period of disease inside the vector after obtaining the virus from the infected plant. Thus, after interacting with an infected vector, the plant demonstrates an incubation time before becoming diseased. This paper analyzes a mathematical model for persistent vector-borne viral plant disease dynamics. The backpropagated neural network based on the Levenberg-Marquardt algorithm (NN-BLMA) is used to study approximate solutions for fluctuations in natural plant mortality and vector mortality rates. A state-of-the-art numerical technique is utilized to generate reference data for obtaining surrogate solutions for multiple cases through NN-BLMA. Curve fitting, regression analysis, error histograms, and convergence analysis are used to assess accuracy of the calculated solutions. It is evident from our simulations that NN-BLMA is accurate and reliable.

Investigation of the Association between the Energy Metabolism of the Insect Vector Laodelphax striatellus and Rice Stripe Virus (RSV)

Viruses, as intracellular parasites, rely on the host organism to complete their life cycle. Although over 70% of plant viruses are transmitted by insect vectors, the role of vector energy metabolism on the infection process of insect-borne plant viruses is unclear. In this study, full-length cDNAs of three energy metabolism-related genes (LsATPase, LsMIT13 and LsNADP-ME) were obtained from the small brown planthopper (SBPH, Laodelphax striatellus), which transmits the Rice stripe virus (RSV). Expression levels of LsATPase, LsMIT13 and LsNADP-ME increased by 105%, 1120% and 259%, respectively, due to RSV infection. The repression of LsATPase, LsMIT13 or LsNADP-ME by RNAi had no effect on RSV nucleocapsid protein (NP) transcripts or protein levels. The repression of LsATPase caused a significant increase in LsMIT13 and LsNADP-ME transcript levels by 230% and 217%, respectively, and the repression of LsMIT13 caused a significant increase in LsNADP-ME mRNA levels. These results suggested that the silencing of LsATPase induced compensatory upregulation of LsMIT13 and LsNADP-ME, and silencing LsMIT13 induced compensatory upregulation of LsNADP-ME. Further study indicated that the co-silencing of LsATPase, LsMIT13 and LsNADP-ME in viruliferous SBPHs increased ATP production and RSV loads by 182% and 117%, respectively, as compared with nonviruliferous SBPHs. These findings indicate that SBPH energy metabolism is involved in RSV infection and provide insight into the association between plant viruses and energy metabolism in the insect vector.

Jingmenviruses: Ubiquitous, understudied, segmented flavi-like viruses

Jingmenviruses are a group of viruses identified recently, in 2014, and currently classified by the International Committee on Taxonomy of Viruses as unclassified Flaviviridae. These viruses closely related to flaviviruses are unique due to the segmented nature of their genome. The prototype jingmenvirus, Jingmen tick virus (JMTV), was discovered in Rhipicephalus microplus ticks collected from China in 2010. Jingmenviruses genomes are composed of four to five segments, encoding for up to seven structural proteins and two non-structural proteins, both of which display strong similarities with flaviviral non-structural proteins (NS2B/NS3 and NS5). Jingmenviruses are currently separated into two phylogenetic clades. One clade includes tick- and vertebrate-associated jingmenviruses, which have been detected in ticks and mosquitoes, as well as in humans, cattle, monkeys, bats, rodents, sheep, and tortoises. In addition to these molecular and serological detections, over a hundred human patients tested positive for jingmenviruses after developing febrile illness and flu-like symptoms in China and Serbia. The second phylogenetic clade includes insect-associated jingmenvirus sequences, which have been detected in a wide range of insect species, as well as in crustaceans, plants, and fungi. In addition to being found in various types of hosts, jingmenviruses are endemic, as they have been detected in a wide range of environments, all over the world. Taken together, all of these elements show that jingmenviruses correspond exactly to the definition of emerging viruses at risk of causing a pandemic, since they are already endemic, have a close association with arthropods, are found in animals in close contact with humans, and have caused sporadic cases of febrile illness in multiple patients. Despite these arguments, the vast majority of published data is from metagenomics studies and many aspects of jingmenvirus replication remain to be elucidated, such as their tropism, cycle of transmission, structure, and mechanisms of replication and restriction or epidemiology. It is therefore crucial to prioritize jingmenvirus research in the years to come, to be prepared for their emergence as human or veterinary pathogens.

Dynamic changes in virus-induced volatiles in cotton modulate the orientation and oviposition behavior of the whitefly Bemisia tabaci

Manipulation of insect vector behavior by virus-induced plant volatiles is well known. But how the viral disease progression alters the plant volatiles and its effect on vector behavior remains less explored. Our studies tracked changes in volatile profile in progressive infection stages of cotton leaf curl virus (CLCuV) infected plants and their effect on B. tabaci behavior. Significant differences in virus titers were noticed between progressive infection stages showing distinct symptoms. Whiteflies initially settled on CLCuV infected plants, but their preference was shifted to healthy plants over time. GC-MS analysis revealed subtle quantitative/qualitative changes in volatile organic compounds (VOCs) between the healthy and selected CLCuV infection stages. VOCs such as hexanal, (E)-2-hexen-1-ol, (+)-α-pinene, (−)-β-pinene, (Z)-3-hexen-1-ol, (+)-sylvestrene, and (1S,2E,6E, 10R)-3,7,11,11-tetramethylbicycloundeca-2,6-diene (Bicyclogermacrene) were associated with the infection stage showing upward curling of leaves; (E)-2-hexen-1-ol, β-myrcene, β-ocimene, and copaene were associated with the infection stage showing downward curling. Validation studies with eight synthetic VOCs indicated that γ-terpinene elicited attraction to B. tabaci (Olfactometric Preference Index (OPI) = 1.65), while β-ocimene exhibited strong repellence (OPI = 0.64) and oviposition reduction (66.01%–92.55%). Our studies have demonstrated that progression of CLCuV disease in cotton was associated with dynamic changes in volatile profile which influences the behavioural responses of whitefly, B.tabaci. Results have shown that VOCs such as (+)-α-pinene, (−)-β-pinene γ-Terpinene, α-guaiene; 4- hydroxy- 4 methyl-2- pentanone and β-ocimene emitted from Begomovirus infected plants could be the driving force for early attraction and later repellence/oviposition deterrence of B. tabaci on virus-infected plants. The findings of this study offer scope for the management of whitefly, B. tabaci through semiochemicals.

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 variables, 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 epidemics 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 temperature 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 nanoplatforms. 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.

Abundance of Poleroviruses within Tasmanian Pea Crops and Surrounding Weeds, and the Genetic Diversity of TuYV Isolates Found

The genus Polerovirus contains positive-sense, single-stranded RNA plant viruses that cause significant disease in many agricultural crops, including vegetable legumes. This study aimed to identify and determine the abundance of Polerovirus species present within Tasmanian pea crops and surrounding weeds that may act as virus reservoirs. We further sought to examine the genetic diversity of TuYV, the most commonly occurring polerovirus identified. Pea and weed samples were collected during 2019-2020 between October and January from thirty-four sites across three different regions (far northwest, north, and midlands) of Tasmania and tested by RT-PCR assay, with selected samples subject to next-generation sequencing. Results revealed that the presence of polerovirus infection and the prevalence of TuYV in both weeds and pea crops varied across the three Tasmanian cropping regions, with TuYV infection levels in pea crops ranging between 0 and 27.5% of tested plants. Overall, two species members from each genus, Polerovirus and Potyvirus, one member from each of Luteovirus, Potexvirus, and Carlavirus, and an unclassified virus from the family Partitiviridae were also found as a result of NGS data analysis. Analysis of gene sequences of the P0 and P3 genes of Tasmanian TuYV isolates revealed substantial genetic diversity within the collection, with a few isolates appearing more closely aligned with BrYV isolates. Questions remain around the differentiation of TuYV and BrYV species. Phylogenetic inconsistency in the P0 and P3 ORFs supports the concept that recombination may have played a role in TuYV evolution in Tasmania. Results of the evolutionary analysis showed that the selection pressure was higher in the P0 gene than in the P3 gene, and the majority of the codons for each gene are evolving under purifying selection. Future full genome-based analyses of the genetic variations will expand our understanding of the evolutionary patterns existing among TuYV populations in Tasmania.

Comparative Plant Transcriptome Profiling of Arabidopsis thaliana Col-0 and Camelina sativa var. Celine Infested with Myzus persicae Aphids Acquiring Circulative and Noncirculative Viruses Reveals Virus- and Plant-Specific Alterations Relevant to Aphid Feeding Behavior and Transmission

Evidence is accumulating that plant viruses alter host plant traits in ways that modify their insect vectors' behavior. These alterations often enhance virus transmission, which has led to the hypothesis that these effects are manipulations caused by viral adaptation. However, we lack a mechanistic understanding of the genetic basis of these indirect, plant-mediated effects on vectors, their dependence on the plant host, and their relation to the mode of virus transmission. Transcriptome profiling of Arabidopsis thaliana and Camelina sativa plants infected with turnip yellows virus (TuYV) or cauliflower mosaic virus (CaMV) and infested with the common aphid vector Myzus persicae revealed strong virus- and host-specific differences in gene expression patterns. CaMV infection caused more severe effects on the phenotype of both plant hosts than did TuYV infection, and the severity of symptoms correlated strongly with the proportion of differentially expressed genes, especially photosynthesis genes. Accordingly, CaMV infection modified aphid behavior and fecundity more strongly than did infection with TuYV. Overall, infection with CaMV, relying on the noncirculative transmission mode, tends to have effects on metabolic pathways, with strong potential implications for insect vector-plant host interactions (e.g., photosynthesis, jasmonic acid, ethylene, and glucosinolate biosynthetic processes), while TuYV, using the circulative transmission mode, alters these pathways only weakly. These virus-induced deregulations of genes that are related to plant physiology and defense responses might impact both aphid probing and feeding behavior on infected host plants, with potentially distinct effects on virus transmission. IMPORTANCE Plant viruses change the phenotype of their plant hosts. Some of the changes impact interactions of the plant with insects that feed on the plants and transmit these viruses. These modifications may result in better virus transmission. We examine here the transcriptomes of two plant species infected with two viruses with different transmission modes to work out whether there are plant species-specific and transmission mode-specific transcriptome changes. Our results show that both are the case.

Occurrence, Distribution, and Transmission of Alfalfa Viruses in China

Alfalfa (Medicago sativa L.) is one of the most important quality forages worldwide and is cultivated throughout China. Alfalfa is susceptible to a variety of viral diseases during its growth, which has caused huge amounts of commercial losses. However, the profile of the alfalfa virus in China remains ambiguous and the viruses transmitted by Odontothrips loti (Haliday), dominant insect pests in alfalfa, are also poorly understood. In the present study, virus diversity was investigated in the primary alfalfa-growing areas in China. A total of 18 alfalfa viruses were identified through RNA-sequencing (RNA-seq) and reverse transcription-polymerase chain reaction (RT-PCR). Two new plant viruses, Medicago sativa virus 1 (MsV1) and Medicago sativa luteovirus 1 (MsLV1), were detected for the first time. Another four viruses, including the Alfalfa ringspot-associated virus (ARaV), Alfalfa virus F (AVF), Alfalfa enamovirus 1 (AEV1), and Alfalfa deltaparitivirus (ADPV), were reported in China for the first time as well. Both Alfalfa mosaic virus (AMV) and Medicago sativa alphapartitivirus 2 (MsAPV2) are the dominant pathogens, with an infection incidence of 91.7-100%, and 74.4-97.2%, respectively. Additionally, O. loti with first- and second-instar nymphs were shown to acquire the AMV within 0.25 h of feeding on a virus-infected alfalfa. Transmission by thrips to healthy alfalfa plants was also demonstrated. Additionally, we clarified the dynamic changes in the AMV in pre-adult stages of O. loti, which indicated that the AMV is propagated in the nymph stage of O. loti. These findings provide valuable information for understanding the alfalfa virome, confirm the role thrips O. loti plays in alfalfa virus transmission, and improve our fundamental knowledge and management of diseases in China.

Pumpkin and watermelon production constraints and management practices in Uganda

BACKGROUND

Watermelons and pumpkins are cultivated in Uganda for their leaves, fruits, and seeds, thereby contributing to food, nutrition and income security. However, there is limited research and information on constraints affecting their production. This study assessed the current production constraints for watermelons and pumpkins, management practices, sources of production inputs to guide research and decision making in production of these crops.

METHODOLOGY

Watermelon and pumpkin fields totalling 105 located in 28 districts from nine sub-regions of Uganda were surveyed. Purposive sampling was conducted based on the importance and availability of watermelon and pumpkin fields in the sub-regions using a questionnaire administered to farmers on different practices, management strategies, and current production constraints. Data were analysed to determine the relationship between the source of seed, sale of their produce, constraints, and control measures of biotic constraints in the different sub-regions.

RESULTS

Pumpkins and watermelons were grown by 85.7% and 14.3% of respondent farmers, respectively. The constraints as ranked by the farmers were pests, diseases, drought, high transport and labour costs. Bacterial wilt, downy mildews, anthracnose powdery mildews and virus diseases in this order were the most common and important disease constraints.The whitefly (Bemisia tabaci, Gennadius), order hemiptera family aleyrodidae, aphids (Myzus Persicae, Sulzer), order hemiptera family aphidadae, melon fly (Bactrocera cucurbitae, Coquillett), order diptera family tephritidae and cutworm (Agrotis ipsilon, Hufnagel), order lepidoptera family noctuidae, were reported as the most limiting pests of watermelon and pumpkin production. Mixing of several agrochemicals was observed in watermelon fields coupled with gross lack of knowledge of proper usage or purpose of these chemicals may result in pesticide resistance, health and environmental hazards.

CONCLUSION

Pests, diseases, and drought constitute the main constraints affecting watermelon and pumpkin cultivation in Uganda. Whereas weeding using hand hoes is the most common method of weed control, application of ash was the main strategy for pest management in pumpkin, while in watermelons, pheromone traps and pesticides were frequently used.

Spatial-temporal distribution of Dalbulus maidis (Hemiptera: Cicadellidae) and factors affecting its abundance in Brazil corn

BACKGROUND

Since the last decade, Dalbulus maidis has become the primary pest in cornfields, particularly due to its ability to transmit plant pathogens. Dalbulus maidis is the main vector of the corn stunt spiroplasma and maize bushy stunt phytoplasma. However, there is little information available on this pest. Understanding its spatial dynamics may allow us to determine how its infestations begin and to identify its colonization patterns, dispersal, and the role of landscape structure on D. maidis dynamics. Thus, this study aimed to investigate within-field spatial distribution and the factors associated with D. maidis abundance in five commercial fields.

RESULTS

In all fields, higher infestations occurred at the boundaries of the central pivot, showing a clear edge-biased distribution. Ranges varied from 100.4 to 611.8 m, and our models' overall fit indicated strong to moderate spatial dependency. Additionally, correlation analyses indicated a positive effect of air temperature on the population of D. maidis. Conversely, rainfall negatively affected D. maidis.

CONCLUSION

This study provides essential guidance for improving D. maidis integrated pest management at regional and local scales. Based on its high dispersal ability, our study suggests the need for a legislative or regulatory method of control for D. maidis, especially in regions where corn has more than one growing season. © 2022 Society of Chemical Industry.

Identification and Characterization of Two Novel Noda-like Viruses from Rice Plants Showing the Dwarfing Symptom

Nodaviruses are small bipartite RNA viruses and are considered animal viruses. Here, we identified two novel noda-like viruses (referred to as rice-associated noda-like virus 1 (RNLV1) and rice-associated noda-like virus 2 (RNLV2)) in field-collected rice plants showing a dwarfing phenotype through RNA-seq. RNLV1 genome consists of 3335 nt RNA1 and 1769 nt RNA2, and RNLV2 genome consists of 3279 nt RNA1 and 1525 nt RNA2. Three conserved ORFs were identified in each genome of the two novel viruses, encoding an RNA-dependent RNA polymerase, an RNA silencing suppressor, and a capsid protein, respectively. The results of sequence alignment, protein domain prediction, and evolutionary analysis indicate that these two novel viruses are clearly different from the known nodaviruses, especially the CPs. We have also determined that the B2 protein encoded by the two new noda-like viruses can suppress RNA silencing in plants. Two reverse genetic systems were constructed and used to show that RNLV1 RNA1 can replicate in plant cells and RNLV1 can replicate in insect Sf9 cells. We have also found two unusual peptidase family A21 domains in the RNLV1 CP, and RNLV1 CP can self-cleave in acidic environments. These findings provide new knowledge of novel nodaviruses.

Nucleoprotein of a Rice Rhabdovirus Serves as the Effector to Attenuate Hemolymph Melanization and Facilitate Viral Persistent Propagation in its Leafhopper Vector

Melanization in the hemolymph of arthropods is a conserved defense strategy against infection by invading pathogens. Numerous plant viruses are persistently transmitted by insect vectors, and must overcome hemolymph melanization. Here, we determine that the plant rhabdovirus rice stripe mosaic virus (RSMV) has evolved to evade the antiviral melanization response in the hemolymph in leafhopepr vectors. After virions enter vector hemolymph cells, viral nucleoprotein N is initially synthesized and directly interacts with prophenoloxidase (PPO), a core component of the melanization pathway and this process strongly activates the expression of PPO. Furthermore, such interaction could effectively inhibit the proteolytic cleavage of the zymogen PPO to active phenoloxidase (PO), finally suppressing hemolymph melanization. The knockdown of PPO expression or treatment with the PO inhibitor also suppresses hemolymph melanization and causes viral excessive accumulation, finally causing a high insect mortality rate. Consistent with this function, microinjection of N into leafhopper vectors attenuates melanization and promotes viral infection. These findings demonstrate that RSMV N serves as the effector to attenuate hemolymph melanization and facilitate viral persistent propagation in its insect vector. Our findings provide the insights in the understanding of ongoing arms race of insect immunity defense and viral counter-defense.

Differential gene expression in aphids following virus acquisition from plants or from an artificial medium

BACKGROUND

Poleroviruses, such as turnip yellows virus (TuYV), are plant viruses strictly transmitted by aphids in a persistent and circulative manner. Acquisition of either virus particles or plant material altered by virus infection is expected to induce gene expression deregulation in aphids which may ultimately alter their behavior.

RESULTS

By conducting an RNA-Seq analysis on viruliferous aphids fed either on TuYV-infected plants or on an artificial medium containing purified virus particles, we identified several hundreds of genes deregulated in Myzus persicae, despite non-replication of the virus in the vector. Only a few genes linked to receptor activities and/or vesicular transport were common between the two modes of acquisition with, however, a low level of deregulation. Behavioral studies on aphids after virus acquisition showed that M. persicae locomotion behavior was affected by feeding on TuYV-infected plants, but not by feeding on the artificial medium containing the purified virus particles. Consistent with this, genes potentially involved in aphid behavior were deregulated in aphids fed on infected plants, but not on the artificial medium.

CONCLUSIONS

These data show that TuYV particles acquisition alone is associated with a moderate deregulation of a few genes, while higher gene deregulation is associated with aphid ingestion of phloem from TuYV-infected plants. Our data are also in favor of a major role of infected plant components on aphid behavior.

In silico analysis of the predicted protein-protein interaction of syntaxin-18, a putative receptor of Peregrinus maidis Ashmead (Hemiptera: Delphacidae) with Maize mosaic virus glycoprotein

The corn planthopper, Peregrinus maidis Ashmead (Hemiptera:Delphacidae), is a widely distributed insect pest which serves as a vector of two phytopathogenic viruses, Maize mosaic virus (MMV) and Maize stripe virus (MStV). It transmits the viruses in a persistent and propagative manner. MMV is an alphanucleorhabdovirus with a negative-sense, single-stranded RNA unsegmented genome. One identified insect vector protein that may serve as receptor to MMV is Syntaxin-18 (PmStx18) which belongs to the SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) proteins. SNAREs play major roles in the final stage of docking and subsequent fusion of diverse vesicle-mediated transport events. In this work, in silico analysis of the interaction of MMV glycoprotein (MMV G) and PmStx18 was performed. Various freely available protein-protein docking web servers were used to predict the 3 D complex of MMV G and PmStx18. Analysis and protein-protein interaction (PPI) count showed that the complex predicted by the ZDOCK server has the highest number of interaction and highest affinity, as suggested by the calculated solvation free energy gain upon formation of the interface (ΔⁱG = -31 kcal/mol). Molecular dynamics simulation of the complex revealed important interactions at the interface over the course of 25 ns. This is the first in silico analysis performed for the interaction on a putative receptor of P. maidis and MMV G. The results of the PPI prediction provide novel information for studying the role of Stx18 in the transport, docking and fusion events involved in virus particle transport in the insect vector cells and its release.Communicated by Ramaswamy H. Sarma.

Dissecting the Species-Specific Virome in Culicoides of Thrace

Biting midges (Culicoides) are vectors of arboviruses of both veterinary and medical importance. The surge of emerging and reemerging vector-borne diseases and their expansion in geographical areas affected by climate change has increased the importance of understanding their capacity to contribute to novel and emerging infectious diseases. The study of Culicoides virome is the first step in the assessment of this potential. In this study, we analyzed the RNA virome of 10 Culicoides species within the geographical area of Thrace in the southeastern part of Europe, a crossing point between Asia and Europe and important path of various arboviruses, utilizing the Ion Torrent next-generation sequencing (NGS) platform and a custom bioinformatics pipeline based on TRINITY assembler and alignment algorithms. The analysis of the RNA virome of 10 Culicoides species resulted in the identification of the genomic signatures of 14 novel RNA viruses, including three fully assembled viruses and four segmented viruses with at least one segment fully assembled, most of which were significantly divergent from previously identified related viruses from the Solemoviridae, Phasmaviridae, Phenuiviridae, Reoviridae, Chuviridae, Partitiviridae, Orthomyxoviridae, Rhabdoviridae, and Flaviviridae families. Each Culicoides species carried a species-specific set of viruses, some of which are related to viruses from other insect vectors in the same area, contributing to the idea of a virus-carrier web within the ecosystem. The identified viruses not only expand our current knowledge on the virome of Culicoides but also set the basis of the genetic diversity of such viruses in the area of southeastern Europe. Furthermore, our study highlights that such metagenomic approaches should include as many species as possible of the local virus-carrier web that interact and share the virome of a geographical area.

Known and Potential Invertebrate Vectors of Raspberry Viruses

The estimated global production of raspberry from year 2016 to 2020 averaged 846,515 tons. The most common cultivated Rubus spp. is European red raspberry (Rubus idaeus L. subsp. idaeus). Often cultivated for its high nutritional value, the red raspberry (Rubus idaeus) is susceptible to multiple viruses that lead to yield loss. These viruses are transmitted through different mechanisms, of which one is invertebrate vectors. Aphids and nematodes are known to be vectors of specific raspberry viruses. However, there are still other potential raspberry virus vectors that are not well-studied. This review aimed to provide an overview of studies related to this topic. All the known invertebrates feeding on raspberry were summarized. Eight species of aphids and seven species of plant-parasitic nematodes were the only proven raspberry virus vectors. In addition, the eriophyid mite, Phyllocoptes gracilis, has been suggested as the natural vector of raspberry leaf blotch virus based on the current available evidence. Interactions between vector and non-vector herbivore may promote the spread of raspberry viruses. As a conclusion, there are still multiple aspects of this topic that require further studies to get a better understanding of the interactions among the viral pathogens, invertebrate vectors, and non-vectors in the raspberry agroecosystem. Eventually, this will assist in development of better pest management strategies.

A Review on Transcriptional Responses of Interactions between Insect Vectors and Plant Viruses

This review provides a synopsis of transcriptional responses pertaining to interactions between plant viruses and the insect vectors that transmit them in diverse modes. In the process, it attempts to catalog differential gene expression pertinent to virus–vector interactions in vectors such as virus reception, virus cell entry, virus tissue tropism, virus multiplication, and vector immune responses. Whiteflies, leafhoppers, planthoppers, and thrips are the main insect groups reviewed, along with aphids and leaf beetles. Much of the focus on gene expression pertinent to vector–virus interactions has centered around whole-body RNA extraction, whereas data on virus-induced tissue-specific gene expression in vectors is limited. This review compares transcriptional responses in different insect groups following the acquisition of non-persistent, semi-persistent, and persistent (non-propagative and propagative) plant viruses and identifies parallels and divergences in gene expression patterns. Understanding virus-induced changes in vectors at a transcriptional level can aid in the identification of candidate genes for targeting with RNAi and/or CRISPR editing in insect vectors for management approaches.

Comparison of Transcriptome Responses between Sogatella furcifera Females That Acquired Southern Rice Black-Streaked Dwarf Virus and Not

Simple Summary

The southern rice black-streaked dwarf virus (SRBSDV) is transmitted horizontally by the planthopper, Sogatella furcifera. During feeding on virus-infected plants, S. furcifera may acquire or fail to acquire SRBSDV. In this study, the responses were compared among the S. furcifera successfully acquiring the virus, those failing to acquire the virus, and those not exposed to SRBSDV (the control). A total of 1043 and 2932 differentially expressed genes (DEGs) were obtained in S. furcifera females that acquired SRBSDV and that failed to, in comparison with the control, respectively. Functionally, these DEGs are primarily involved in diverse signaling pathways related to primary metabolism and innate immunity, such as apoptosis. Additional bioassays confirmed the activation of apoptosis in S. furcifera by SRBSDV exposure. Interestingly, we also found that six female-specific genes were also upregulated in S. furcifera females exposed to SRBSDV. Our results further the understanding of the interactions between the vector S. furcifera females and SRBSDV at the molecular level.

Abstract

The southern rice black-streaked dwarf virus (SRBSDV) is transmitted horizontally by Sogatella furcifera in a persistent, propagative manner. Exposure of S. furcifera females to SRBSDV-infected rice plants may trigger transcriptomic changes in the insects, the transcriptomes of females that acquired SRBSDV and those that failed to, as well as females fed on healthy rice plants as control, were sequenced and compared. Nine transcriptomic libraries were constructed, from which a total of 53,084 genes were assembled. Among the genes, 1043 and 2932 were differentially expressed genes (DEGs) in S. furcifera females that acquired SRBSDV and that failed to, in comparison with the control, respectively. Functional enrichment analysis showed that DEGs identified in S. furcifera females exposed to SRBSDV are primarily involved in diverse signaling pathways related to primary metabolism and innate immunity. The DEGs in the S. furcifera females that failed to acquire the virus significantly outnumbered that in the insects that acquired the virus, and the virus exposure activated the humoral and cellular immune responses of the vectors, especially the apoptosis. The key gene in apoptosis encoding caspase 1 was upregulated by SRBSDV exposure, especially in S. furcifera females that failed to acquire the virus. Analysis of caspase 1 activity validated that SRBSDV exposure induced caspase 1 accumulation. Surprisingly, the expression of six female-specific genes was also upregulated by SRBSDV exposure, which was confirmed by RT-qPCR analysis. This study provides evidence to explain the differential virus acquisition at the transcriptome level.

A cytorhabdovirus-based expression vector in Nilaparvata lugens, Laodelphax striatellus, and Sogatella furcifera

The brown planthopper (BPH, Nilaparvata lugens), the small brown planthopper (SBPH, Laodelphax striatellus), and the white-backed planthopper (WBPH, Sogatella furcifera) are problematic insect pests and cause severe yield losses through phloem sap-sucking and virus transmission. Barley yellow striate mosaic virus (BYSMV), a plant cytorhabdovirus, has been developed as versatile expression platforms in SBPHs and cereal plants. However, bio-safe overexpression vectors based on recombinant BYSMV (rBYSMV) remain to be developed and applied to the three kinds of planthoppers. Here, we found that rBYSMV was able to infect SBPHs, BPHs and WBPHs through microinjection with crude extracts from rBYSMV-infected barley leaves. To ensure bio-safety of the rBYSMV vectors, we generated an rBYSMV mutant by deleting the accessory protein P3, a putative viral movement protein. As expected, the resulting mutant abolished viral systemic infection in barley plants but had no effects on BYSMV infectivity in insect vectors. Subsequently, we used the modified rBYSMV vector to overexpress iron transport peptide (ITP) in the three kinds of planthoppers and revealed the potential functions of ITP. Overall, our results provide bio-safe overexpression platforms to facilitate functional genomics studies of planthoppers.

Transcriptome of the Maize Leafhopper (Dalbulus maidis) and Its Transcriptional Response to Maize Rayado Fino Virus (MRFV), Which It Transmits in a Persistent, Propagative Manner

The corn leafhopper (Dalbulus maidis) is an important vector of maize rayado fino virus (MRFV), a positive-strand RNA (+ssRNA) marafivirus which it transmits in a persistent propagative manner. The interaction of D. maidis with MRFV, including infection of the insect and subsequent transmission to new plants, is not well understood at the molecular level. To examine the leafhopper-virus interaction, a D. maidis transcriptome was assembled and differences in transcript abundance between virus-exposed and naive D. maidis were examined at two time points (4 h and 7 days) post exposure to MRFV. The D. maidis transcriptome contained 56,116 transcripts generated from 1,727,369,026 100-nt paired-end reads from whole adult insects. The transcriptome of D. maidis shared highest identity and most orthologs with the leafhopper Graminella nigrifrons (65% of transcripts had matches with E values of <10^-5) versus planthoppers Sogatella furcifera (with 23% of transcript matches below the E value cutoff) and Peregrinus maidis (with 21% transcript matches below the E value cutoff), as expected based on taxonomy. D. maidis expressed genes in the Toll, Imd, and Jak/Stat insect immune signaling pathways, RNA interference (RNAi) pathway genes, prophenoloxidase-activating system pathways, and immune recognition protein-encoding genes such as peptidoglycan recognition proteins (PGRPs), antimicrobial peptides, and other effectors. Statistical analysis (performed by R package DESeq2) identified 72 transcripts at 4 h and 67 at 7 days that were significantly responsive to MRFV exposure. Genes expected to be favorable for virus propagation, such as protein synthesis-related genes and genes encoding superoxide dismutase, were significantly upregulated after MRFV exposure. IMPORTANCE The transcriptome of the corn leafhopper, D. maidis, revealed conserved biochemical pathways for immunity and discovered transcripts responsive to MRFV-infected plants at two time points, providing a basis for functional identification of genes that either limit or promote the virus-vector interaction. Compared to other hopper species and the propagative plant viruses they transmit, D. maidis shared 15 responsive transcripts with S. furcifera (to southern rice black-streaked dwarf virus [SRBSDV]), one with G. nigrifrons (to maize fine streak virus [MFSV]), and one with P. maidis (to maize mosaic virus [MMV]), but no virus-responsive transcripts identified were shared among all four hopper vector species.

The Amino-Proximal Region of the Coat Protein of Cucumber Vein Yellowing Virus (Family Potyviridae) Affects the Infection Process and Whitefly Transmission

Most plant viruses rely on vector transmission for their spread and specific interactions between vector and virus have evolved to regulate this relationship. The whitefly Bemisia tabaci- transmitted cucumber vein yellowing virus (CVYV; genus Ipomovirus, family Potyviridae) is endemic in the Mediterranean Basin, where it causes significant losses in cucurbit crops. In this study, the role of the coat protein (CP) of CVYV for B. tabaci transmission and plant infection was investigated using a cloned and infectious CVYV cDNA and a collection of point and deletion mutants derived from this clone. Whitefly transmission of CVYV was abolished in a deletion mutant lacking amino acids in position 93-105 of the CP. This deletion mutant caused more severe disease symptoms compared to the cDNA clone representing the wild-type (wt) virus and movement efficiency was likewise affected. Two virus mutants carrying a partially restored CP were transmissible and showed symptoms comparable to the wt virus. Collectively, our data demonstrate that the N-terminus of the CVYV CP is a determinant for transmission by the whitefly vector and is involved in plant infection and symptom expression.

Plant proteomic research for improvement of food crops under stresses: a review

Crop improvement approaches have been changed due to technological advancements in traditional plant-breeding methods. Abiotic and biotic stresses limit plant growth and development, which ultimately lead to reduced crop yield. Proteins encoded by genomes have a considerable role in the endurance and adaptation of plants to different environmental conditions. Biotechnological applications in plant breeding depend upon the information generated from proteomic studies. Proteomics has a specific advantage to contemplate post-translational modifications, which indicate the functional effects of protein modifications on crop production. Subcellular proteomics helps in exploring the precise cellular responses and investigating the networking among subcellular compartments during plant development and biotic/abiotic stress responses. Large-scale mass spectrometry-based plant proteomic studies with a more comprehensive overview are now possible due to dramatic improvements in mass spectrometry, sample preparation procedures, analytical software, and strengthened availability of genomes for numerous plant species. Development of stress-tolerant or resilient crops is essential to improve crop productivity and growth. Use of high throughput techniques with advanced instrumentation giving efficient results made this possible. In this review, the role of proteomic studies in identifying the stress-response processes in different crops is summarized. Advanced techniques and their possible utilization on plants are discussed in detail. Proteomic studies accelerate marker-assisted genetic augmentation studies on crops for developing high yielding stress-tolerant lines or varieties under stresses.

Grapevine Red Blotch Virus Is Transmitted by the Three-Cornered Alfalfa Hopper in a Circulative, Nonpropagative Mode with Unique Attributes

The transmission mode of grapevine red blotch virus (GRBV, genus Grablovirus, family Geminiviridae) by Spissistilus festinus, the three-cornered alfalfa hopper, is unknown. By analogy with other members in the family Geminiviridae, we hypothesized circulative, nonpropagative transmission. Time-course experiments revealed GRBV in dissected guts, hemolymph, and heads with salivary glands after a 5-, 8-, and 10-day exposure to infected grapevines, respectively. After a 15-day acquisition on infected grapevines and subsequent transfer on alfalfa, a nonhost of GRBV, the virus titer decreased over time in adult insects, as shown by quantitative PCR. Snap bean proved to be a feeding host of S. festinus and a pseudosystemic host of GRBV after Agrobacterium tumefaciens-mediated delivery of an infectious clone. The virus was efficiently transmitted by S. festinus from infected snap bean plants to excised snap bean trifoliates (90%) or grapevine leaves (100%) but less efficiently from infected grapevine plants to excised grapevine leaves (10%) or snap bean trifoliates (67%). Transmission of GRBV also occurred trans-stadially but not via seeds. The virus titer was significantly higher in (i) guts and hemolymph relative to heads with salivary glands, and (ii) adults emanating from third compared with first instars that emerged on infected grapevine plants and developed on snap bean trifoliates. This study demonstrated circulative, nonpropagative transmission of GRBV by S. festinus with an extended acquisition access period compared with other viruses in the family Geminiviridae and marked differences in transmission efficiency between grapevine, the natural host, and snap bean, an alternative herbaceous host.

Genetic diversity and molecular characterization of Cucumber mosaic cucumovirus (CMV) subgroup II infecting Spinach (Spinacia oleracea) and Pea (Pisum sativum) in Pothwar region of Pakistan

Cucumber mosaic virus (CMV) is a tremendous threat to vegetables across the globe, including in Pakistan. The present work was conducted to investigate the genetic variability of CMV isolates infecting pea and spinach vegetables in the Pothwar region of Pakistan. Serological-based surveys during 2016-2017 revealed 31.70% overall CMV disease incidence from pea and spinach crops. Triple-antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) revealed that all the positive isolates belong to CMV subgroup II. Two selected cDNA from ELISA-positive samples representing each pea and spinach crops were PCR-amplified (ca.1100 bp) and sequenced corresponding to the CMV CP gene which shared 93.7% nucleotide identity with each other. Both the sequences of CMV pea (AAHAP) and spinach (AARS) isolates from Pakistan were submitted to GenBank as accession nos. MH119071 and MH119073, respectively. BLAST analysis revealed 93.4% sequence identity of AAHAP isolate with SpK (KC763473) from Iran while AARS isolate shared maximum identity (94.5%) with the strain 241 (AJ585519) from Australia and clustered with some reference isolates of CMV subgroup II from UK (Z12818) and USA (AF127976) in a Neighbour-joining phylogenetic reconstruction. A total of 59 polymorphic (segregating) sites (S) with nucleotide diversity (π) of 0.06218 was evident while no INDEL event was observed in Pakistani isolates. The evolutionary distance of Pakistani CMV isolates was recorded as 0.0657 with each other and 0.0574-0.2964 with other CMV isolates reported elsewhere in the world. A frequent gene flow (Fst = 0.30478 <0.33) was observed between Pakistani and earlier reported CMV isolates. In genetic differentiation analysis, the value of three permutation-based statistical tests viz; Z (84.3011), Snn (0.82456), and Ks* (4.04042) were non-significant. The statistical analysis revealed the values 2.02535, 0.01468, and 0.71862 of Tajima's D, Fu, & Li's F* and D* respectively, demonstrating that the CMV population is under balancing selection.

Characterization of the virome associated with Haemagogus mosquitoes in Trinidad, West Indies

Currently, there are increasing concerns about the possibility of a new epidemic due to emerging reports of Mayaro virus (MAYV) fever outbreaks in areas of South and Central America. Haemagogus mosquitoes, the primary sylvan vectors of MAYV are poorly characterized and a better understanding of the mosquito's viral transmission dynamics and interactions with MAYV and other microorganisms would be important in devising effective control strategies. In this study, a metatranscriptomic based approach was utilized to determine the prevalence of RNA viruses in field-caught mosquitoes morphologically identified as Haemagogus janthinomys from twelve (12) forest locations in Trinidad, West Indies. Known insect specific viruses including the Phasi Charoen-like and Humaiata-Tubiacanga virus dominated the virome of the mosquitoes throughout sampling locations while other viruses such as the avian leukosis virus, MAYV and several unclassified viruses had a narrower distribution. Additionally, assembled contigs from the Ecclesville location suggests the presence of a unique uncharacterized picorna-like virus. Mapping of RNA sequencing reads to reference mitochondrial sequences of potential feeding host animals showed hits against avian and rodent sequences, which putatively adds to the growing body of evidence of a potentially wide feeding host-range for the Haemagogus mosquito vector.