Proteomic Analysis of Interaction between a Plant Virus and Its Vector Insect Reveals New Functions of Hemipteran Cuticular Protein

The cuticular protein gene ApCP7 and ApCP62 are essential for reproduction in Acyrthosiphon pisum, affecting ecdysis and survival

Cuticular proteins, in conjunction with chitin, compose the insect exoskeleton, and play a key role in the growth, development, and molting of insects. However, the specific functions of most cuticular protein genes in the growth, development, and reproductive processes of the pea aphid (Acyrthosiphon pisum) remain unclear. In this study, we have identified six cuticular protein genes in the pea aphid, namely ApCP7, ApCP10, ApCP19, ApCP19.8-like, ApCP35 and ApCP62. We found that the expression levels of six genes were highly expressed during the adult stage, and except for ApCP10, which is highly expressed in the pea aphid cuticle, other genes were highly expressed in the ovaries. Subsequently, we observed that the survival rate and fecundity of pea aphid were significantly lower than those of the control group after silencing ApCP7 and ApCP62 through RNA interference. Furthermore, when ApCP7 transcript levels were reduced, aphid encountered difficulties in molting, were smaller in body size, and exhibited a darker body color. These results indicate that ApCP7 and ApCP62 are involved in the development and reproduction of pea aphid, and could be used as RNAi targets for controlling pea aphid.

Genome-wide identification of cuticle protein superfamily in Frankliniella occidentalis provide insight into the control of both insect vectors and plant virus

The structural cuticle proteins (CPs) play important roles in the development and fitness of insects. However, knowledge about CP gene superfamily is limited in virus-transmitting insect vectors, although its importance on transmission of plant virus has been gradually emphasized. In this study, the genome-wide identification of CP superfamily was conducted in western flower thrips Frankliniella occidentalis that is the globally invasive pest and plant virus vector pest. The pest transmits notorious tomato spotted wilt virus (TSWV) around the world, causing large damage to a wide array of plants. One hundred and twenty-eight F. occidentalis CP genes (FoCPs) were annotated in this study and they were classified into 10 distinct families, including 68 CPRs, 16 CPAP1s, 6 CPAP3s, 2 CPCFCs, 10 Tweedles, 4 CPFs, 16 CPLCPs, and 6 CPGs. The comprehensive analysis was performed including phylogenetic relationship, gene location and gene expression profiles during different development stages of F. occidentalis. Transcriptome analysis revealed more than 30% FoCPs were upregulated at least 1.5-fold when F. occidentalis was infected by TSWV, indicating their potential involvement in TSWV interactions. Our study provided an overview of F. occidentalis CP superfamily. The study gave a better understand of CP's role in development and virus transmission, which provided clues for reducing viral damages through silencing CP genes in insect vectors.

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 plant-encoded 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.

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.

A call to arms: novel strategies for thrips and tospovirus control

Thrips and the tospoviruses they transmit are some of the most significant threats to food and ornamental crop production globally. Control of the insect and virus is challenging and new strategies are needed. Characterizing the thrips-virus interactome provides new targets for disrupting the transmission cycle. Viral and insect determinants of vector competence are being defined, including the viral attachment protein and its structure as well as thrips proteins that interact with and respond to tospovirus infection. Additional thrips control strategies such as RNA interference need further refinement and field-applicable delivery systems, but they show promise for the knockdown of essential genes for thrips survival and virus transmission. The identification of a toxin that acts to deter thrips oviposition on cotton also presents new opportunities for control of this important pest.

Over-expression of CP9 and CP83 increases whitefly cell cuticle thickness leading to imidacloprid resistance

Cuticular proteins (CPs) play an important role in protecting insects from adverse environmental conditions, like neonicotinoid insecticides, which are heavily used for numerous pests and caused environmental problems and public health concerns worldwide. However, the relationship between CPs and insecticides resistance in Bemisia tabaci, a serious and developed high insecticide resistance, is lacking. In this study, 125 CPs genes were identified in B. tabaci. Further phylogenetic tree showed the RR-2-type genes formed large gene groups in B. tabaci. Transcriptional expression levels of CPs genes at different developmental stages revealed that some CPs genes may play a specific role in insect development. The TEM results indicated that the cuticle thickness of susceptible strain was thinner than imidacloprid-resistance strain. Furthermore, 16 CPs genes (5 in RR-1 subfamily, 7 in RR-2 subfamily, 3 in CPAP3 subfamily and 1 in CPCFC subfamily) were activated in response to imidacloprid. And RNAi results indicated that CP9 and CP83 involved in imidacloprid resistance. In conclusion, this study was the first time to establish a basic information framework and evolutionary relationship between CPs and imidacloprid resistance in B. tabaci, which provides a basis for proposing integrated pest management strategies.

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.

Southern rice black-streaked dwarf virus induces incomplete autophagy for persistence in gut epithelial cells of its vector insect

Autophagy plays an important role in virus infection of the host, because viral components and particles can be degraded by the host's autophagy and some viruses may be able to hijack and subvert autophagy for its benefit. However, details on the mechanisms that govern autophagy for immunity against viral infections or benefit viral survival remain largely unknown. Plant reoviruses such as southern rice black-streaked dwarf virus (SRBSDV), which seriously threaten crop yield, are only transmitted by vector insects. Here, we report a novel mechanism by which SRBSDV induces incomplete autophagy by blocking autophagosome-lysosome fusion, resulting in viral accumulation in gut epithelial cells of its vector, white-backed planthopper (Sogatella furcifera). SRBSDV infection leads to stimulation of the c-Jun N-terminal kinase (JNK) signaling pathway, which further activates autophagy. Mature and assembling virions were found close to the edge7 of the outer membrane of autophagosomes. Inhibition autophagy leads to the decrease of autophagosomes, which resulting in impaired maturation of virions and the decrease of virus titer, whereas activation of autophagy facilitated virus titer. Further, SRBSDV inhibited fusion of autophagosomes and lysosomes by interacting with lysosomal-associated membrane protein 1 (LAMP1) using viral P10. Thus, SRBSDV not only avoids being degrading by lysosomes, but also further hijacks these non-fusing autophagosomes for its subsistence. Our findings reveal a novel mechanism of reovirus persistence, which can explain why SRBSDV can be acquired and transmitted rapidly by its insect vector.

The effects of the E3 ubiquitin-protein ligase UBR7 of Frankliniella occidentalis on the ability of insects to acquire and transmit TSWV

The interactions between plant viruses and insect vectors are very complex. In recent years, RNA sequencing data have been used to elucidate critical genes of Tomato spotted wilt ortho-tospovirus (TSWV) and Frankliniella occidentalis (F. occidentalis). However, very little is known about the essential genes involved in thrips acquisition and transmission of TSWV. Based on transcriptome data of F. occidentalis infected with TSWV, we verified the complete sequence of the E3 ubiquitin-protein ligase UBR7 gene (UBR7), which is closely related to virus transmission. Additionally, we found that UBR7 belongs to the E3 ubiquitin-protein ligase family that is highly expressed in adulthood in F. occidentalis. UBR7 could interfere with virus replication and thus affect the transmission efficiency of F. occidentalis. With low URB7 expression, TSWV transmission efficiency decreased, while TSWV acquisition efficiency was unaffected. Moreover, the direct interaction between UBR7 and the nucleocapsid (N) protein of TSWV was investigated through surface plasmon resonance and GST pull-down. In conclusion, we found that UBR7 is a crucial protein for TSWV transmission by F. occidentalis, as it directly interacts with TSWV N. This study provides a new direction for developing green pesticides targeting E3 ubiquitin to control TSWV and F. occidentalis.

Proteomic and Transcriptomic Analysis for Identification of Endosymbiotic Bacteria Associated with BYDV Transmission Efficiency by Sitobion miscanthi

Sitobion miscanthi, an important viral vector of barley yellow dwarf virus (BYDV), is also symbiotically associated with endosymbionts, but little is known about the interactions between endosymbionts, aphid and BYDV. Therefore, two aphids' geographic populations, differing in their BYDV transmission efficiency, after characterizing their endosymbionts, were treated with antibiotics to investigate how changes in the composition of their endosymbiont population affected BYDV transmission efficiency. After antibiotic treatment, Rickettsia was eliminated from two geographic populations. BYDV transmission efficiency by STY geographic population dropped significantly, by -44.2% with ampicillin and -25.01% with rifampicin, but HDZ geographic population decreased by only 14.19% with ampicillin and 23.88% with rifampicin. Transcriptomic analysis showed that the number of DEGs related to the immune system, carbohydrate metabolism and lipid metabolism did increase in the STY rifampicin treatment, while replication and repair, glycan biosynthesis and metabolism increased in the STY ampicillin treatment. Proteomic analysis showed that the abundance of symbionin symL, nascent polypeptide-associated complex subunit alpha and proteasome differed significantly between the two geographic populations. We found that the endosymbionts can mediate vector viral transmission. They should therefore be included in investigations into aphid-virus interactions and plant disease epidemiology. Our findings should also help with the development of strategies to prevent virus transmission.

The physical interactome between Peregrinus maidis proteins and the maize mosaic virus glycoprotein provides insights into the cellular biology of a rhabdovirus in the insect vector

Rhabdovirus glycoproteins (G) serve multifunctional roles in virus entry, assembly, and exit from animal cells. We hypothesize that maize mosaic virus (MMV) G is required for invasion, infection, and spread in Peregrinus maidis, the planthopper vector. Using a membrane-based yeast two-hybrid assay, we identified 107 P. maidis proteins that physically interacted with MMV G, of which approximately 53% matched proteins with known functions including endocytosis, vesicle-mediated transport, protein synthesis and turnover, nuclear export, metabolism and host defense. Physical interaction networks among conserved proteins indicated a possible cellular coordination of processes associated with MMV G translation, protein folding and trafficking. Non-annotated proteins contained predicted functional sites, including a diverse array of ligand binding sites. Cyclophilin A and apolipophorin III co-immunoprecipitated with MMV G, and each showed different patterns of localization with G in insect cells. This study describes the first protein interactome for a rhabdovirus spike protein and insect vector.

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.

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.

Comprehensive analysis of lysine lactylation in Frankliniella occidentalis

Western flower thrips (Frankliniella occidentalis) are among the most important pests globally that transmit destructive plant viruses and infest multiple commercial crops. Lysine lactylation (Klac) is a recently discovered novel post-translational modification (PTM). We used liquid chromatography-mass spectrometry to identify the global lactylated proteome of F. occidentalis, and further enriched the identified lactylated proteins using Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). In the present study, we identified 1,458 Klac sites in 469 proteins from F. occidentalis. Bioinformatics analysis showed that Klac was widely distributed in F. occidentalis proteins, and these Klac modified proteins participated in multiple biological processes. GO and KEGG enrichment analysis revealed that Klac proteins were significantly enriched in multiple cellular compartments and metabolic pathways, such as the ribosome and carbon metabolism pathways. Two Klac proteins were found to be involved in the regulation of the TSWV (Tomato spotted wilt virus) transmission in F. occidentalis. This study provides a systematic report and a rich dataset of lactylation in F. occidentalis proteome for potential studies on the Klac protein of this notorious pest.

Comparative transcriptome profiling reveals a network of differentially expressed genes in Asia II 7 and MEAM1 whitefly cryptic species in response to early infection of Cotton leaf curl Multan virus

Cotton leaf curl Multan virus (CLCuMuV) is a whitefly-vectored begomovirus that poses ramping threat to several economically important crops worldwide. The differential transmission of CLCuMuV by its vector Bemisia tabaci mainly relies on the type of whitefly cryptic species. However, the molecular responses among different whitefly cryptic species in response to early CLCuMuV infection remain elusive. Here, we compared early-stage transcriptomic profiles of Asia II 7 and MEAM1 cryptic species infected by CLCuMuV. Results of Illumina sequencing revealed that after 6 and 12 h of CLCuMuV acquisition, 153 and 141 genes among viruliferous (VF) Asia II 7, while 445 and 347 genes among VF MEAM 1 whiteflies were differentially expressed compared with aviruliferous (AVF) whiteflies. The most abundant groups of differentially expressed genes (DEGs) among Asia II 7 and MEAM1 were associated with HTH-1 and zf-C2H2 classes of transcription factors (TFs), respectively. Notably, in contrast to Asia II 7, MEAM1 cryptic species displayed higher transcriptional variations with elevated immune-related responses following CLCuMuV infection. Among both cryptic species, we identified several highly responsive candidate DEGs associated with antiviral innate immunity (alpha glucosidase, LSM14-like protein B and phosphoenolpyruvate carboxykinase), lysosome (GPI-anchored protein 58) and autophagy/phagosome pathways (sequestosome-1, cathepsin F-like protease), spliceosome (heat shock protein 70), detoxification (cytochrome P450 4C1), cGMP-PKG signaling pathway (myosin heavy chain), carbohydrate metabolism (alpha-glucosidase), biological transport (mitochondrial phosphate carrier) and protein absorption and digestion (cuticle protein 8). Further validation of RNA-seq results showed that 23 of 28 selected genes exhibited concordant expression both in RT-qPCR and RNA-seq. Our findings provide vital mechanistic insights into begomovirus-whitefly interactions to understand the dynamics of differential begomovirus transmission by different whitefly cryptic species and reveal novel molecular targets for sustainable management of insect-transmitted plant viruses.

Isobaric tags for relative and absolute quantification-based proteomic analysis of host-pathogen protein interactions in the midgut of Aedes albopictus during dengue virus infection

Aedes albopictus (Ae. albopictus), an important vector of dengue virus (DENV), is distributed worldwide. Identifying host proteins involved in flavivirus replication in Ae. albopictus and determining their natural antiviral mechanisms are critical to control virus transmission. Revealing the key proteins related to virus replication and exploring the host-pathogen interaction are of great significance in finding new pathways of the natural immune response in Ae. albopictus. Isobaric tags for relative and absolute quantification (iTRAQ) was used to perform a comparative proteomic analysis between the midgut of Ae. albopictus infected with DENV and the control. 3,419 proteins were detected, of which 162 were ≥ 1.2-fold differentially upregulated or ≤ 0.8-fold differentially downregulated (p < 0.05) during DENV infections. Differentially expressed proteins (DEPs) were mainly enriched in ubiquitin ligase complex, structural constituent of cuticle, carbohydrate metabolism, and lipid metabolism pathways. We found that one of the DEPs, a putative pupal cuticle (PC) protein could inhibit the replication of DENV and interact with the DENV-E protein. In addition, the result of immunofluorescence (IF) test showed that there was co-localization between ubiquitin carboxyl-terminal hydrolase (UCH) protein and the DENV-E protein, and virus infection reduced the level of this protein. iTRAQ-based proteomic analysis of the Ae. albopictus midgut identified dengue infection-induced upregulated and downregulated proteins. The interaction between the PC and UCH proteins in the midgut of Ae. albopictus might exert a natural antiviral mechanism in mosquito.

Proteome-wide analysis of lysine 2-hydroxyisobutyrylation in Frankliniella occidentalis

BACKGROUND

Lysine 2-hydroxyisobutyrylation (Khib) is a novel and conserved post-translational modification (PTM). Frankliniella occidentalis are economically important agricultural pests globally and also notorious for vectoring destructive plant viruses. To better study the disease transmission mechanism of F. occidentalis, it is necessary to conduct in-depth analysis of it. So far, no Khib modification of insects has been reported.

RESULTS

In this study, a proteome-wide analysis of Khib modifications in F. occidentalis was analyzed for the first time through the combination of high performance liquid chromatography fractionation technology and 2-hydroxyisobutyrylated peptide enrichment and other advanced technologies, 4093 Khib sites were identified on 1125 modified proteins. Bioinformatics and functional enrichment analyses showed that Khib-modified proteins were significantly enriched in many cell compartments and pathways, especially related to various cellular components and biological processes, and were more concentrated in ribosomes and proteasome subunits, involved in energy metabolism, protein synthesis and degradation, compared to the other nine species including Japonica rice, Homo sapiens, P. patens, Botrytis, Ustilaginoidea virens, Saccharomyces cerevisiae, T. gondii, C. albicans, and F. oxysporum. And Khib sites on virus-interacting insect proteins were discovered for the first time, such as cyclophilin and endoCP-GN.

CONCLUSIONS

After three repeated experiments, we found a total of 4093 Khib sites on 1125 proteins. These modified proteins are mainly concentrated in ribosomes and proteasome subunits, and are widely involved in a variety of critical biological activities and metabolic processes of F. occidentalis. In addition, for the first time, Khib modification sites are found on the proteome of F. occidentalis, and these sites could be acted as for the virus interaction, including cyclophilin and endoCP-GN. The global map of 2-hydroxyisobutyrylation in thrips is an invaluable resource to better understand the biological processes of thrips and provide new means for disease control and mitigation of pest damage to crops.

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.

Heat shock cognate protein 70 is required for rice stripe tenuivirus accumulation and transmission in small brown planthopper

Rice stripe tenuivirus (RSV) is mainly transmitted by the insect vector small brown planthopper (SBPH, Laodelphax striatellus) in a persistent-propagative manner. Virus transmission is dependent on the interplay between viral proteins and vector factors. Pc2, a nonstructural protein of RSV, plays an important role in virus transmission. However, the vector proteins that interact with Pc2 are unknown. In this study, we identified three SBPH proteins that interact with the N-terminal 381 amino acids of Pc2 (Pc2N) by using a yeast two-hybrid system (Y2H). The interaction of Pc2N with heat shock protein cognate 70 (HSC70) was studied further. HSC70 was verified to interact with RSV Pc2N by biomolecular fluorescence complementation and co-immunoprecipitation assays. HSC70 colocalized with RSV Pc2N in both Sf9 cells and the hemocytes of SBPHs. Inhibition of HSC70 expression via RNA interference reduced virus levels in hemolymph and salivary glands of SBPHs and resulted in decreased virus transmission efficiency. These data provide evidence that a vector protein, HSC70, is employed by RSV to facilitate virus accumulation in the hemolymph and thereby promote virus transmission. These findings are important for a better understanding of the interactions between plant viruses and insect vectors.

A novel tenuivirus infecting wheat in Brazil

Since 1948, pale yellow wheat spike have been reported in southern Brazil. This symptom was associated with tenuiviruses due to the observation of cytoplasmic inclusions constituted by a mass of filamentous particles (7-10 nm in diameter) with indeterminate length, identical to those found in "leaf dip" preparations. Such symptoms are still seen in wheat crops; however, there is a lack of information regarding this pathosystem. Decades after the first report, the first sequences of wheat white spike virus were characterized. Wheat plants with symptoms such as pale yellowing, chlorotic streaks, and leaf mosaic were collected in Paraná State, Southern Brazil. High-throughput sequencing was used to determine the nearly complete nucleotide sequence of the viral genome. The genome is composed of five RNAs with a total size of 18,129 nucleotides, with eight open reading frames (ORFs). The virus identified in this study can be included in a new species in the family Phenuiviridae, genus Tenuivirus, and we have tentatively named this virus "wheat white spike virus".

Roles of Bacterial Symbionts in Transmission of Plant Virus by Hemipteran Vectors

The majority of plant viruses are transmitted by hemipteran insects. Bacterial symbionts in hemipteran hosts have a significant impact on the host life, physiology and ecology. Recently, the involvement of bacterial symbionts in hemipteran vector-virus and vector-plant interactions has been documented. Thus, the exploitation and manipulation of bacterial symbionts have great potential for plant viral disease control. Herein, we review the studies performed on the impact of symbiotic bacteria on plant virus transmission, including insect-bacterial symbiont associations, the role of these bacterial symbionts in viral acquisition, stability and release during viral circulation in insect bodies, and in viral vertical transmission. Besides, we prospect further studies aimed to understand tripartite interactions of the virus-symbiotic microorganisms-insect vector.

Southern rice black-streaked dwarf virus hijacks SNARE complex of its insect vector for its effective transmission to rice

Vesicular trafficking is an important dynamic process that facilitates intracellular transport of biological macromolecules and their release into the extracellular environment. However, little is known about whether or how plant viruses utilize intracellular vesicles to their advantage. Here, we report that southern rice black-streaked dwarf virus (SRBSDV) enters intracellular vesicles in epithelial cells of its insect vector by engaging VAMP7 and Vti1a proteins in the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. The major outer capsid protein P10 of SRBSDV was shown to interact with VAMP7 and Vti1a of the white-backed planthopper and promote the fusion of vesicles into a large vesicle, which finally fused with the plasma membrane to release virions from midgut epithelial cells. Downregulation of the expression of either VAMP7 or Vti1a did not affect viral entry and accumulation in the gut, but significantly reduced viral accumulation in the haemolymph. It also did not affect virus acquisition, but significantly reduced the virus transmission efficiency to rice. Our data reveal a critical mechanism by which a plant reovirus hijacks the vesicle transport system to overcome the midgut escape barrier in vector insects and provide new insights into the role of the SNARE complex in viral transmission and the potential for developing novel strategies of viral disease control.

RNA N6 -methyladenosine modification suppresses replication of rice black streaked dwarf virus and is associated with virus persistence in its insect vector

N⁶ methylation of adenosine (m⁶ A) was recently discovered to play a role in regulating the life cycle of various viruses by modifying viral and host RNAs. However, different studies on m⁶ A effects on the same or different viruses have revealed contradictory roles for m⁶ A in the viral life cycle. In this study, we sought to define the role of m⁶ A on infection by rice black streaked dwarf virus (RBSDV), a double-stranded RNA virus, of its vector small brown planthopper (SBPH). Infection by RBSDV decreased the level of m⁶ A in midgut cells of SBPHs. We then cloned two genes (LsMETTL3 and LsMETTL14) that encode m⁶ A RNA methyltransferase in SBPHs. After interference with expression of the two genes, the titre of RBSDV in the midgut cells of SBPHs increased significantly, suggesting that m⁶ A levels were negatively correlated with virus replication. More importantly, our results revealed that m⁶ A modification might be the epigenetic mechanism that regulates RBSDV replication in its insect vector and maintains a certain virus threshold required for persistent transmission.

Rice stripe virus: Exploring Molecular Weapons in the Arsenal of a Negative-Sense RNA Virus

Rice stripe disease caused by Rice stripe virus (RSV) is one of the most devastating plant viruses of rice and causes enormous losses in production. RSV is transmitted from plant to plant by the small brown planthopper (Laodelphax striatellus) in a circulative-propagative manner. The recent reemergence of this pathogen in East Asia since 2000 has made RSV one of the most studied plant viruses over the past two decades. Extensive studies of RSV have resulted in substantial advances regarding fundamental aspects of the virus infection. Here, we compile and analyze recent information on RSV with a special emphasis on the strategies that RSV has adopted to establish infections. These advances include RSV replication and movement in host plants and the small brown planthopper vector, innate immunity defenses against RSV infection, epidemiology, and recent advances in the management of rice stripe disease. Understanding these issues will facilitate the design of novel antiviral therapies for management and contribute to a more detailed understanding of negative-sense virus-host interactions at the molecular level.

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.

Completion of Maize Stripe Virus Genome Sequence and Analysis of Diverse Isolates

Maize stripe virus is a pathogen of corn and sorghum in subtropical and tropical regions worldwide. We used high-throughput sequencing to obtain the complete nucleotide sequence for the reference genome of maize stripe virus and to sequence the genomes of ten additional isolates collected from the United States or Papua New Guinea. Genetically, maize stripe virus is most closely related to rice stripe virus. We completed and characterized the RNA1 sequence for maize stripe virus, which revealed a large open reading frame encoding a putative protein with ovarian tumor-like cysteine protease, endonuclease, and RNA-dependent RNA polymerase domains. Phylogenetic and amino acid identity analyses among geographically diverse isolates revealed evidence for reassortment in RNA3 that was correlated with the absence of RNA5. This study yielded a complete and updated genetic description of the tenuivirus maize stripe virus and provided insight into potential mechanisms underpinning its diversity.

Affinity Purification-Mass Spectrometry Identifies a Novel Interaction between a Polerovirus and a Conserved Innate Immunity Aphid Protein that Regulates Transmission Efficiency

The vast majority of plant viruses are transmitted by insect vectors, with many crucial aspects of the transmission process being mediated by key protein-protein interactions. Still, very few vector proteins interacting with viruses have been identified and functionally characterized. Potato leafroll virus (PLRV) is transmitted most efficiently by Myzus persicae, the green peach aphid, in a circulative, non-propagative manner. Using affinity purification coupled to high-resolution mass spectrometry (AP-MS), we identified 11 proteins from M. persicaedisplaying a high probability of interaction with PLRV and an additional 23 vector proteins with medium confidence interaction scores. Three of these aphid proteins were confirmed to directly interact with the structural proteins of PLRV and other luteovirid species via yeast two-hybrid. Immunolocalization of one of these direct PLRV-interacting proteins, an orthologue of the human innate immunity protein complement component 1 Q subcomponent-binding protein (C1QBP), shows that MpC1QBP partially co-localizes with PLRV in cytoplasmic puncta and along the periphery of aphid gut epithelial cells. Artificial diet delivery to aphids of a chemical inhibitor of C1QBP leads to increased PLRV acquisition by aphids and subsequently increased titer in inoculated plants, supporting a role for C1QBP in the acquisition and transmission efficiency of PLRV by M. persicae. This study presents the first use of AP-MS for the in vivo isolation of a functionally relevant insect vector-virus protein complex. MS data are available from ProteomeXchange.org using the project identifier PXD022167.

The Bunyavirales: The Plant-Infecting Counterparts

Negative-strand (-) RNA viruses (NSVs) comprise a large and diverse group of viruses that are generally divided in those with non-segmented and those with segmented genomes. Whereas most NSVs infect animals and humans, the smaller group of the plant-infecting counterparts is expanding, with many causing devastating diseases worldwide, affecting a large number of major bulk and high-value food crops. In 2018, the taxonomy of segmented NSVs faced a major reorganization with the establishment of the order Bunyavirales. This article overviews the major plant viruses that are part of the order, i.e., orthospoviruses (Tospoviridae), tenuiviruses (Phenuiviridae), and emaraviruses (Fimoviridae), and provides updates on the more recent ongoing research. Features shared with the animal-infecting counterparts are mentioned, however, special attention is given to their adaptation to plant hosts and vector transmission, including intra/intercellular trafficking and viral counter defense to antiviral RNAi.

Proteomic analysis of Laodelphax striatellus in response to Rice stripe virus infection reveal a potential role of ZFP36L1 in restriction of viral proliferation

Persistent plant viruses multiply and circulate inside insect vectors following the route of midgut-hemolymph-salivary gland. Currently, how viruses interact with insect vectors after they are released into hemolymph is not entirely clear. In this study, we found that the hemolymph and fat body (HF) contained the highest Rice stripe virus (RSV) levels. Proteomic analysis on RSV-free and RSV-infected HF identified 156 differentially expressed proteins (DEPs), with the majority of them participating in metabolism, transportation, and detoxification. The RNA binding protein esf2 was the most downregulated protein. Knocking down the expression of esf2 did not influence the RSV burden, but caused the lethal effect to L. striatellus. In contrast, the mRNA decay protein ZFP36L1 was 69% more abundant upon RSV infection, and suppression of ZFP36L1 significantly increased the RSV burden. Our results reveal the potential role of ZFP36L1 in restricting the viral proliferation, and provide valuable clues for unravelling the interaction between RSV and L. striatellus in HF. SIGNIFICANCE: More than 76% of plant viruses are transmitted by insect vectors. For persistent propagative transmission, plant viruses multiply and circulate inside insects following the route of midgut-hemolymph-salivary gland. However, how viruses interact with vector insects after they are released into hemolymph is not entirely clear. Our study investigated the influence of rice stripe virus (RSV) on insect hemolymph and fat body by iTRAQ labeling method. Among the 156 differentially expressed proteins (DEPs) identified, two proteins associated with mRNA metabolism were selected for function analysis. We found that the mRNA decay activator protein ZFP36L1 influenced the RSV proliferation, and RNA binding protein esf2 caused the lethal effect to L. striatellus. Our results provide valuable clues for unveiling the interaction between RSV and L. striatellus, and might be useful in pest management.

Silencing of ATP synthase β reduces phytoplasma multiplication in a leafhopper vector

The leafhopper Euscelidius variegatus is a natural vector of the chrysanthemum yellows phytoplasma (CYp) and a laboratory vector of the Flavescence dorée phytoplasma (FDp). Previous studies indicated a crucial role for insect ATP synthase α and β subunits during phytoplasma infection of the vector species. Gene silencing of ATP synthase β was obtained by injection of specific dsRNAs in E. variegatus. Here we present the long-lasting nature of such silencing, its effects on the small RNA profile, the significant reduction of the corresponding protein expression, and the impact on phytoplasma acquisition capability. The specific transcript expression was silenced at least up to 37 days post injection with an average reduction of 100 times in insects injected with dsRNAs targeting ATP synthase β (dsATP) compared with those injected with dsRNAs targeting green fluorescent protein (dsGFP), used as negative controls. Specific silencing of this gene was also confirmed at protein level at 15 days after the injection. Total sRNA reads mapping to dsATP and dsGFP sequences in analysed libraries showed in both cases a peak of 21 nt, a length consistent with the generation of dsRNA-derived siRNAs by RNAi pathway. Reads mapped exclusively to the fragment corresponding to the injected dsATPs, probably indicating the absence of a secondary machinery for siRNA synthesis. Insects injected either with dsATP or dsGFP successfully acquired CYp and FDp during feeding on infected plants. However, the average phytoplasma amount in dsATP insects was significantly lower than that measured in dsGFP specimens, indicating a probable reduction of the pathogen multiplication when ATP synthase β was silenced. The role of the insect ATP synthase β during phytoplasma infection process is discussed.

Ribavirin targets sugar transporter 6 to suppress acquisition and transmission of rice stripe tenuivirus by its vector Laodelphax striatellus

BACKGROUND

Rice stripe tenuivirus (RSV) is one of the most destructive pathogens of rice and other cereal crops. The virus is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a circulative-propagative manner. Thus, blocking transmission by the insect vector would provide an effective strategy to prevent epidemic outbreaks of the disease.

RESULTS

In this study, we explored the effect of ribavirin on acquisition and transmission of the virus by specifically inhibiting the expression of sugar transporter 6 (LsSt-6), which was recently reported as a key vector component for RSV transmission. Ribavirin at the highest concentration tested (250 μmol L^-1 ) significantly reduced RSV acquisition and transmission efficiency by SBPHs through inhibiting LsSt-6 messenger RNA (mRNA) level. Survival of the model insect Spodoptera frugiperda cell line (Sf9) was 95.0 ± 2.2 and 85.6 ± 2.1% after exposure to 250 μmol L^-1 ribavirin or 8-azaguanine, respectively. Further study confirmed that 250 μmol L^-1 ribavirin also significantly reduced LsSt-6 mRNA and protein levels in Sf9 cells. However, 8-azaguanine did not significantly inhibit viral infectivity and LsSt-6 mRNA levels in SBPH or the Sf9 cell line.

CONCLUSION

This result provides evidence that ribavirin has the potential to disrupt LsSt-6 expression but not others like viral RNAs to prevent acquiring RSV, which leads to less viral accumulation in SBPH tissues and thereby lower transmission efficiency. © 2020 Society of Chemical Industry.

Imaginal disc growth factor maintains cuticle structure and controls melanization in the spot pattern formation of Bombyx mori

The complex stripes and patterns of insects play key roles in behavior and ecology. However, the fine-scale regulation mechanisms underlying pigment formation and morphological divergence remain largely unelucidated. Here we demonstrated that imaginal disc growth factor (IDGF) maintains cuticle structure and controls melanization in spot pattern formation of Bombyx mori. Moreover, our knockout experiments showed that IDGF is suggested to impact the expression levels of the ecdysone inducible transcription factor E75A and pleiotropic factors apt-like and Toll8/spz3, to further control the melanin metabolism. Furthermore, the untargeted metabolomics analyses revealed that BmIDGF significantly affected critical metabolites involved in phenylalanine, beta-alanine, purine, and tyrosine metabolism pathways. Our findings highlighted not only the universal function of IDGF to the maintenance of normal cuticle structure but also an underexplored space in the gene function affecting melanin formation. Therefore, this study furthers our understanding of insect pigment metabolism and melanin pattern polymorphisms.

The diverse stripe patterns of animals are usually used for warning or camouflage. However, the actual mechanisms underlying diverse stripe pattern formation remains largely unknown. This study provides direct evidence that imaginal disc growth factor (IDGF) maintains cuticle structure and controls melanization in the spot pattern formation. Our exhaustive knockout experiments reveal that BmIDGF is involved in the melanin pigmentation of Bombyx mori. We demonstrate that IDGF impacts the expression levels of the 20E-inducible transcription factor E75A and pleiotropic factors apt-like and Toll8/spz3, to further affect the melanin metabolism. Furthermore, the metabolome of BmIDGF gene deletion connects metabolism to gene function. Thus, this study shed light on not only the unique function of IDGF but also the molecular mechanism of spot pattern formation.

A Plant Virus Ensures Viral Stability in the Hemolymph of Vector Insects through Suppressing Prophenoloxidase Activation

Large ratios of vector-borne plant viruses circulate in the hemolymph of their vector insects before entering the salivary glands to be transmitted to plants. The stability of virions in the hemolymph is vital in this process. Activation of the proteolytic prophenoloxidase (PPO) to produce active phenoloxidase (PO) is one of the major innate immune pathways in insect hemolymph. How a plant virus copes with the PPO immune reaction in its vector insect remains unclear. Here, we report that the PPO affects the stability of rice stripe virus (RSV), a notorious rice virus, in the hemolymph of a vector insect, the small brown planthopper. RSV suppresses PPO activation using viral nonstructural protein. Once the level of PO activity is elevated, RSV is melanized and eliminated from the hemolymph. Our work gives valuable clues for developing novel strategies for controlling the transmission of vector-borne plant viruses.

Most plant viruses require vector insects for transmission. Viral stability in the hemolymph of vector insects is a prerequisite for successful transmission of persistent plant viruses. However, knowledge of whether the proteolytic activation of prophenoloxidase (PPO) affects the stability of persistent plant viruses remains elusive. Here, we explored the interplay between rice stripe virus (RSV) and the PPO cascade of the vector small brown planthopper. Phenoloxidase (PO) activity was suppressed by RSV by approximately 60%. When the PPO cascade was activated, we found distinct melanization around RSV particles and serious damage to viral stability in the hemolymph. Viral suppression of PO activity was derived from obstruction of proteolytic cleavage of PPOs by binding of the viral nonstructural protein NS3. These results indicate that RSV attenuates the PPO response to ensure viral stability in the hemolymph of vector insects. Our research provides enlightening cues for controlling the transmission of vector-borne viruses.

Applications of Proteomic Tools to Study Insect Vector-Plant Virus Interactions

Proteins are crucial players of biological interactions within and between the organisms and thus it is important to understand the role of proteins in successful partnerships, such as insect vectors and their plant viruses. Proteomic approaches have identified several proteins at the interface of virus acquisition and transmission by their insect vectors which could be potential molecular targets for sustainable pest and viral disease management strategies. Here we review the proteomic techniques used to study the interactions of insect vector and plant virus. Our review will focus on the techniques available to identify the infection, global changes at the proteome level in insect vectors, and protein-protein interactions of insect vectors and plant viruses. Furthermore, we also review the integration of other techniques with proteomics and the available bioinformatic tools to analyze the proteomic data.

The α-tubulin of Laodelphax striatellus mediates the passage of rice stripe virus (RSV) and enhances horizontal transmission

Rice stripe virus (RSV, genus Tenuivirus, family Phenuiviridae) is the causal agent of rice stripe disease transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a persistent propagative manner. The midgut and salivary glands of SBPH are the first and last barriers to the viral circulation and transmission processes, respectively; however, the precise mechanisms used by RSV to cross these organs and transmit to rice plants have not been fully elucidated. We obtained the full-length cDNA sequence of L. striatellus α-tubulin 2 (LsTUB) and found that RSV infection increased the level of LsTUB in vivo. Furthermore, LsTUB was shown to co-localize with RSV nonstructural protein 3 (NS3) in vivo and bound NS3 at positions 74-76 and 80-82 in vitro. Transient gene silencing of LsTUB expression caused a significant reduction in detectable RSV loads and viral NS3 expression levels, but had no effect on NS3 silencing suppressor activity and viral replication in insect cells. However, suppression of LsTUB attenuated viral spread in the bodies of SBPHs and decreased RSV transmission rates to rice plants. Electrical penetration graphs (EPG) showed that LsTUB knockdown by RNAi did not impact SBPH feeding; therefore, the reduction in RSV transmission rates was likely caused by a decrease in viral loads inside the planthopper. These findings suggest that LsTUB mediates the passage of RSV through midgut and salivary glands and leads to successful horizontal transmission.

Suppression of Rice Stripe Virus Replication in Laodelphax striatellus Using Vector Insect-Derived Double-Stranded RNAs

RNA interference (RNAi) has attracted attention as a promising approach to control plant viruses in their insect vectors. In the present study, to suppress replication of the rice stripe virus (RSV) in its vector, Laodelphax striatellus, using RNAi, dsRNAs against L. striatellus genes that are strongly upregulated upon RSV infection were delivered through a rice leaf-mediated method. RNAi-based silencing of peroxiredoxin, cathepsin B, and cytochrome P450 resulted in significant down regulation of the NS3 gene of RSV, achieving a transcriptional reduction greater than 73.6% at a concentration of 100 ng/μl and, possibly compromising viral replication. L. striatellus genes might play crucial roles in the transmission of RSV; transcriptional silencing of these genes could suppress viral replication in L. striatellus. These results suggest effective RNAi-based approaches for controlling RSV and provide insight into RSV-L. striatellus interactions.

Cuticular Structure Proteomics in the Pea Aphid Acyrthosiphon pisum Reveals New Plant Virus Receptor Candidates at the Tip of Maxillary Stylets

Aphids are phloem-feeding insects known as major pests in agriculture that are able to transmit hundreds of plant viruses. The majority of these viruses, classified as noncirculative, are retained and transported on the inner surface of the cuticle of the needle-like mouthparts while the aphids move from plant to plant. Identification of receptors of viruses within insect vectors is a key challenge because they are promising targets for alternative control strategies. The acrostyle, an organ discovered earlier within the common food/salivary canal at the tip of aphid maxillary stylets, displays proteins at the cuticle-fluid interface, some of which are receptors of noncirculative viruses. To assess the presence of stylet- and acrostyle-specific proteins and identify putative receptors, we have developed a comprehensive comparative analysis of the proteomes of four cuticular anatomical structures of the pea aphid, stylets, antennae, legs, and wings. In addition, we performed systematic immunolabeling detection of the cuticular proteins identified by mass spectrometry in dissected stylets. We thereby establish the first proteome of stylets of an insect and determine the minimal repertoire of the cuticular proteins composing the acrostyle. Most importantly, we propose a short list of plant virus receptor candidates, among which RR-1 proteins are remarkably predominant. The data are available via ProteomeXchange (PXD016517).

New Technologies for Studying Negative-Strand RNA Viruses in Plant and Arthropod Hosts

The plant viruses in the phylum Negarnaviricota, orders Bunyavirales and Mononegavirales, have common features of single-stranded, negative-sense RNA genomes and replication in the biological vector. Due to the similarities in biology, comparative functional analysis in plant and vector hosts is helpful for understanding host-virus interactions for negative-strand RNA viruses. In this review, we will highlight recent technological advances that are breaking new ground in the study of these recalcitrant virus systems. The development of infectious clones for plant rhabdoviruses and bunyaviruses is enabling unprecedented examination of gene function in plants and these advances are also being transferred to study virus biology in the vector. In addition, genome and transcriptome projects for critical nonmodel arthropods has enabled characterization of insect response to viruses and identification of interacting proteins. Functional analysis of genes using genome editing will provide future pathways for further study of the transmission cycle and new control strategies for these viruses and their vectors.

High Diversity and Functional Complementation of Alimentary Canal Microbiota Ensure Small Brown Planthopper to Adapt Different Biogeographic Environments

Almost all insects harbor commensal bacteria in the alimentary canal lumen or within cells and often play a pivotal role in their host’s development, evolution, and environmental adaptation. However, little is known about the alimentary canal microbiota and their functions in sap-sucking insect pests of crops, which can damage plants by removing plant sap and by transmitting various plant viruses, especially in the small brown planthopper, Laodelphax striatellus. In this study, we characterized the alimentary canal microbiota of L. striatellus collected from seven regions in China by sequencing 16S rDNA. The insects harbored a rich diversity of microbes, mainly consisted of bacteria from phyla Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Tenericutes. The composition and abundance of microbiota were more similar as the geographic distance decreased between the populations and clustered by geographic location into three groups: temperate, subtropical, and tropical populations. Although the abundance and species of microbes differed among the populations, the various major microbes for each population performed similar functions based on a clusters of orthologous group analysis. Greater diversity in ecological factors in different regions might lead to higher microbial diversity, thus enabling L. striatellus to adapt or tolerate various extreme environments to avoid the cost of long-distance migration. Moreover, the abundance of various metabolic functions in the Kaifeng populations might contribute to higher fecundity in L. striatellus.

A novel cuticle protein involved in WSSV infection to the Pacific white shrimp Litopenaeus vannamei

As the most productive crustacean species in aquaculture, Litopenaeus vannamei is seriously threatened by white spot syndrome virus (WSSV), which has caused huge economic damage in the past decades. Shrimp cuticle proteins are the important components in the frontier target tissues, including cuticle and the chitinous lining of the digestive tract. In present study, a novel cuticle protein gene, named LvCPAP1, was isolated and demonstrated to play an important role in WSSV infection. The deduced amino acid sequence of LvCPAP1 contained a signal peptide and a conserved chitin-binding domain type 2 (ChBD2). Tissue distribution analysis revealed that LvCPAP1 was predominantly expressed in epidermis and stomach. The transcription levels of LvCPAP1 in epidermis and stomach were significantly regulated upon WSSV challenge. DsRNA silencing of LvCPAP1 decreased the in vivo WSSV copy numbers and the death rate of shrimp after WSSV infection, indicating that LvCPAP1 might facilitate WSSV invasion. In addition, the interaction between LvCPAP1 and the major envelop protein VP24 of WSSV was revealed by yeast two-hybrid system and further confirmed by dot blot and pull-down assays. The present study implied that cuticle protein LvCPAP1 might favor the entry process of WSSV, which provided new clues for understanding the role of cuticle proteins during virus infection.

Cell Biology During Infection of Plant Viruses in Insect Vectors and Plant Hosts

Plant viruses typically cause severe pathogenicity in plants, even resulting in the death of plants. Many pathogenic plant viruses are transmitted in a persistent manner via insect vectors. Interestingly, unlike in the plant hosts, persistent viruses are either nonpathogenic or show limited pathogenicity in their insect vectors, while taking advantage of the cellular machinery of insect vectors for completing their life cycles. This review discusses why persistent plant viruses are nonpathogenic or have limited pathogenicity to their insect vectors while being pathogenic to plants hosts. Current advances in cell biology of virus-insect vector interactions are summarized, including virus-induced inclusion bodies, changes of insect cellular ultrastructure, and immune response of insects to the viruses, especially autophagy and apoptosis. The corresponding findings of virus-plant interactions are compared. An integrated view of the balance strategy achieved by the interaction between viral attack and the immune response of insect is presented. Finally, we outline progress gaps between virus-insect and virus-plant interactions, thus highlighting the contributions of cultured cells to the cell biology of virus-insect interactions. Furthermore, future prospects of studying the cell biology of virus-vector interactions are presented.

Discovery of Novel Thrips Vector Proteins That Bind to the Viral Attachment Protein of the Plant Bunyavirus Tomato Spotted Wilt Virus

The plant-pathogenic virus tomato spotted wilt virus (TSWV) encodes a structural glycoprotein (GN) that, like with other bunyavirus/vector interactions, serves a role in viral attachment and possibly in entry into arthropod vector host cells. It is well documented that Frankliniella occidentalis is one of nine competent thrips vectors of TSWV transmission to plant hosts. However, the insect molecules that interact with viral proteins, such as GN, during infection and dissemination in thrips vector tissues are unknown. The goals of this project were to identify TSWV-interacting proteins (TIPs) that interact directly with TSWV GN and to localize the expression of these proteins in relation to virus in thrips tissues of principal importance along the route of dissemination. We report here the identification of six TIPs from first-instar larvae (L1), the most acquisition-efficient developmental stage of the thrips vector. Sequence analyses of these TIPs revealed homology to proteins associated with the infection cycle of other vector-borne viruses. Immunolocalization of the TIPs in L1 revealed robust expression in the midgut and salivary glands of F. occidentalis, the tissues most important during virus infection, replication, and plant inoculation. The TIPs and GN interactions were validated using protein-protein interaction assays. Two of the thrips proteins, endocuticle structural glycoprotein and cyclophilin, were found to be consistent interactors with GN These newly discovered thrips protein-GN interactions are important for a better understanding of the transmission mechanism of persistent propagative plant viruses by their vectors, as well as for developing new strategies of insect pest management and virus resistance in plants.IMPORTANCE Thrips-transmitted viruses cause devastating losses to numerous food crops worldwide. For negative-sense RNA viruses that infect plants, the arthropod serves as a host as well by supporting virus replication in specific tissues and organs of the vector. The goal of this work was to identify thrips proteins that bind directly to the viral attachment protein and thus may play a role in the infection cycle in the insect. Using the model plant bunyavirus tomato spotted wilt virus (TSWV), and the most efficient thrips vector, we identified and validated six TSWV-interacting proteins from Frankliniella occidentalis first-instar larvae. Two proteins, an endocuticle structural glycoprotein and cyclophilin, were able to interact directly with the TSWV attachment protein, GN, in insect cells. The TSWV GN-interacting proteins provide new targets for disrupting the viral disease cycle in the arthropod vector and could be putative determinants of vector competence.

Entry of bunyaviruses into plants and vectors

The majority of plant-infecting viruses are transmitted by arthropod vectors that deliver them directly into a living plant cell. There are diverse mechanisms of transmission ranging from direct binding to the insect stylet (non-persistent transmission) to persistent-propagative transmission in which the virus replicates in the insect vector. Despite this diversity in interactions, most arthropods that serve as efficient vectors have feeding strategies that enable them to deliver the virus into the plant cell without extensive damage to the plant and thus effectively inoculate the plant. As such, the primary virus entry mechanism for plant viruses is mediated by the biological vector. Remarkably, viruses that are transmitted in a propagative manner (bunyaviruses, rhabdoviruses, and reoviruses) have developed an ability to replicate in hosts from two kingdoms. Viruses in the order Bunyavirales are of emerging importance and with the advent of new sequencing technologies, we are getting unprecedented glimpses into the diversity of these viruses. Plant-infecting bunyaviruses are transmitted in a persistent, propagative manner must enter two unique types of host cells, plant and insect. In the insect phase of the virus life cycle, the propagative viruses likely use typical cellular entry strategies to traverse cell membranes. In this review, we highlight the transmission and entry strategies of three genera of plant-infecting bunyaviruses: orthotospoviruses, tenuiviruses, and emaraviruses.

Exogenous H2S reduces the acetylation levels of mitochondrial respiratory enzymes via regulating the NAD+-SIRT3 pathway in cardiac tissues of db/db mice

Hydrogen sulfide (H₂S), a gaseous molecule, is involved in modulating multiple physiological functions, such as antioxidant, antihypertension, and the production of polysulfide cysteine. H₂S may inhibit reactive oxygen species generation and ATP production through modulating respiratory chain enzyme activities; however, the mechanism of this effect remains unclear. In this study, db/db mice, neonatal rat cardiomyocytes, and H9c2 cells treated with high glucose, oleate, and palmitate were used as animal and cellular models of type 2 diabetes. The mitochondrial respiratory rate, respiratory chain complex activities, and ATP production were decreased in db/db mice compared with those in db/db mice treated with exogenous H₂S. Liquid chromatography with tandem mass spectrometry analysis showed that the acetylation level of proteins involved in the mitochondrial respiratory chain were increased in the db/db mice hearts compared with those with sodium hydrosulfide (NaHS) treatment. Exogenous H₂S restored the ratio of NAD⁺/NADH, enhanced the expression and activity of sirtuin 3 (SIRT3) and decreased mitochondrial acetylation level in cardiomyocytes under hyperglycemia and hyperlipidemia. As a result of SIRT3 activation, acetylation of the respiratory complexe enzymes NADH dehydrogenase 1 (ND1), ubiquinol cytochrome c reductase core protein 1, and ATP synthase mitochondrial F1 complex assembly factor 1 was reduced, which enhanced the activities of the mitochondrial respiratory chain activity and ATP production. We conclude that exogenous H₂S plays a critical role in improving cardiac mitochondrial function in diabetes by upregulating SIRT3.

Evaluation of Rice stripe virus transmission efficiency by quantification of viral load in the saliva of insect vector

BACKGROUND

Persistent plant viruses transfer from insect gut to the hemolymph, and finally to the salivary glands before inoculation into the plant hosts with saliva during insect feeding. Virus accumulation in saliva is an important indicator for the transmission ability of an insect vector. In order to evaluate the transmission ability of the small brown planthopper to rice stripe virus (RSV), we successfully measured accumulation of RSV in the saliva of planthoppers via the absolute real-time quantitative polymerase chain reaction method by quantifying the copy numbers of viral genes.

RESULTS

After feeding on an artificial diet for 24 h, the copy numbers of viral genes of capsid protein (CP) and disease-specific protein (SP) can be detected in the saliva collected from as few as ten viruliferous planthoppers and ten non-viruliferous planthoppers after infected with RSV for 7 days. When the expression of planthopper G protein pathway suppressor 2 or c-Jun N-terminal kinase was knocked down, the copy numbers of CP and SP in the saliva varied accordingly.

CONCLUSION

Our study provided an accurate and convenient detection system to evaluate the transmission efficiency of RSV by small brown planthoppers, and this method may also be suitable for other persistent plant viruses. © 2019 Society of Chemical Industry.

Immune function of an angiotensin-converting enzyme against Rice stripe virus infection in a vector insect

Angiotensin-converting enzyme (ACE) plays diverse roles in the animal kingdom. However, whether ACE plays an immune function against viral infection in vector insects is unclear. In this study, an ACE gene (LsACE) from the small brown planthopper was found to respond to Rice stripe virus (RSV) infection. The enzymatic activities of LsACE were characterized at different pH and temperature. Twenty planthopper proteins were found to interact with LsACE. RSV infection significantly upregulated LsACE expression in the testicle and fat body. When the expression of LsACE in viruliferous planthoppers was inhibited, the RNA level of the RSV SP gene was upregulated 2-fold in planthoppers, and all RSV genes showed higher RNA levels in the rice plants consumed by these planthoppers, leading to a higher viral infection rate and disease rating index. These results indicate that LsACE plays a role in the immune response against RSV transmission by planthoppers.

The vitellogenin receptor has an essential role in vertical transmission of rice stripe virus during oogenesis in the small brown plant hopper

BACKGROUND

The small brown plant hopper (SBPH), Laodelphax striatellus Fallén, is one of the most destructive pests on rice. This pest transmits rice stripe virus (RSV) both horizontally and vertically, leading to major yield and economic losses in rice production. However, the way that RSV particles enter oocytes of SBPH remains largely unknown. Thus, identification of key factors involved in the interaction between SBPH and RSV in the ovary is crucial.

RESULTS

Transcriptome of non-viruliferous (NV) or high viruliferous (HV) SBPH ovaries at 24 and 48 h of emergence was sequenced. Differentially expressed genes analysis showed that vitellogenin receptor was significantly highly expressed in the ovary of the HV SBPH strains compared to NV strains. Quantitative real-time polymer chain reaction showed that the vitellogenin receptor in L. striatellus (LsVgR) was highly expressed in the ovaries of female adults and maintained a high level of expression at the early stage of ovary development. By using RNA interference, the expression of LsVgR in the ovaries of the HV strain was significantly decreased by 98.1%. RSV titer was reduced by 60.9% as quantified by viral RNA3 intergenic region and the transcripts of nucleocapsid protein gene (CP) reduced by 46.3%. The numbers of offspring hatched were significantly reduced in dsRNA-treated groups. The transcripts of CP were not affected by silencing LsVgR, whereas the abundance of RNA-dependent RNA polymerase increased by 15-fold in the member of surviving progenies.

CONCLUSION

Our results suggest that vitellogenin receptor participates in regulating RSV replication during oogenesis. © 2018 Society of Chemical Industry.