Plasmodesmata-associated Flotillin positively regulates broad-spectrum virus cell-to-cell trafficking.

Viral diseases seriously threaten rice production. Plasmodesmata (PD)-associated proteins are deemed to play a key role in viral infection in host plants. However, few PD-associated proteins have been discovered in rice to afford viral infection. Here, inspired by the infection mechanism in insect vectors, we identified a member of the Flotillin family taking part in the cell-to-cell transport of rice stripe virus (RSV) in rice. Flotillin1 interacted with RSV nucleocapsid protein (NP) and was localized on PD. In flotillin1 knockout mutant rice, which displayed normal growth, RSV intercellular movement was retarded, leading to significantly decreased disease incidence. The PD pore sizes of the mutant rice were smaller than those of the wild type due to more callose deposits, which was closely related to the upregulation of two callose synthase genes. RSV infection stimulated flotillin1 expression and enlarged the PD aperture via RSV NP. In addition, flotillin1 knockout decreased disease incidences of southern rice black-streaked dwarf virus (SRBSDV) and rice dwarf virus (RDV) in rice. Overall, our study reveals a new PD-associated protein facilitating virus cell-to-cell trafficking and presents the potential of flotillin1 as a target to produce broad-spectrum antiviral rice resources in the future.

Resistance to Planthoppers and Southern Rice Black-Streaked Dwarf Virus in Rice Germplasms.

The damage caused by the white-back planthopper (WBPH, Sogatella furcifera) and brown planthopper (BPH, Nilaparvata lugens), as well as southern rice black-streaked dwarf virus (SRBSDV), considerably decreases the grain yield of rice. Identification of rice germplasms with sufficient resistance to planthoppers and SRBSDV is essential to the breeding and deployment of resistant varieties and, hence, the control of the pests and disease. In this study, 318 rice accessions were evaluated for their reactions to the infestation of both BPH and WBPH at the seedling stage using the standard seed-box screening test method; insect quantification was further conducted at the end of the tillering and grain-filling stages in field trials. Accessions HN12-239 and HN12-328 were resistant to both BPH and WBPH at all tested stages. Field trials were conducted to identify resistance in the collection to SRBSDV based on the virus infection rate under artificial inoculation. Rathu Heenati (RHT) and HN12-239 were moderately resistant to SRBSDV. In addition, we found that WBPH did not penetrate stems with stylets but did do more probing bouts and xylem sap ingestion when feeding on HN12-239 than the susceptible control rice Taichung Native 1. The resistance of rice accessions HN12-239, HN12-328, and RHT to BPH, WBPH, and/or SRBSDV should be valuable to the development of resistant rice varieties.

An aspartic protease 47 causes quantitative recessive resistance to rice black-streaked dwarf virus disease and southern rice black-streaked dwarf virus disease.

Rice black-streaked dwarf virus disease (RBSDVD) and southern rice black-streaked dwarf virus disease (SRBSDVD) are the most destructive viral diseases in rice. Progress is limited in breeding due to lack of resistance resource and inadequate knowledge on the underlying functional gene. Using genome-wide association study (GWAS), linkage disequilibrium (LD) decay analyses, RNA-sequencing, and genome editing, we identified a highly RBSDVD-resistant variety and its first functional gene. A highly RBSDVD-resistant variety W44 was identified through extensive evaluation of a diverse international rice panel. Seventeen quantitative trait loci (QTLs) were identified among which qRBSDV6-1 had the largest phenotypic effect. It was finely mapped to a 0.8-1.2 Mb region on chromosome 6, with 62 annotated genes. Analysis of the candidate genes underlying qRBSDV6-1 showed high expression of aspartic proteinase 47 (OsAP47) in a susceptible variety, W122, and a low resistance variety, W44. OsAP47 overexpressing lines exhibited significantly reduced resistance, while the knockout mutants exhibited significantly reduced SRBSDVD and RBSDVD severity. Furthermore, the resistant allele Hap1 of OsAP47 is almost exclusive to Indica, but rare in Japonica. Results suggest that OsAP47 knockout by editing is effective for improving RBSDVD and SRBSDVD resistance. This study provides genetic information for breeding resistant cultivars.

Evaluation of reference genes and expression of key genes involved in the isoprenoid metabolic pathway of rice leaves after infection by the Southern rice black-streaked dwarf virus.

The Southern rice black-streaked dwarf virus (SRBSDV), a novel Fijivirus, poses a major threat to rice production in East Asia. Analysis of the gene expression of SRBSDV-infected rice plants may reveal the molecular basis of interactions between the virus, its vector and rice plants. Reliable reference genes are required for accurate qRT-PCR analysis. However, no reliable, valid reference genes for examining gene expression in SRBSDV-infected rice plants have so far been identified. We examined the expression of eight candidate reference genes in the leaves of SRBSDV-infected, and healthy, rice plants at different points in time after virus inoculation. We used four dedicated algorithms, geNorm, BestKeeper, NormFinder and RefFinder, to evaluate the performance of these candidate genes. The RefFinder results indicate that 18S, EF1α and UBQ10 are suitable reference genes. In addition, we used these three reference genes to analyze the expression of key genes involved in the isoprenoid metabolic pathway in rice leaves after infection by SRBSDV. The results of this analysis reveal that SRBSDV may suppress the production of the rice plant volatiles that attract natural enemies of its vector Sogatella furcifera, thereby increasing the likelihood of pathogen transmission.

Co-infection of two reoviruses increases both viruses accumulation in rice by up-regulating of viroplasm components and movement proteins bilaterally and RNA silencing suppressor unilaterally.

BACKGROUND: Synergism between southern rice black-streaked dwarf virus (SRBSDV) and rice ragged stunt virus (RRSV) not only aggravates disease symptoms but also enhances their vector acquisition efficiencies by increasing both viruses' titers in co-infected rice plants, which may exacerbate the epidemic of both viruses and cause significant damage to rice production. The molecular mechanism of viral synergism of these two viruses remains unexplored. METHODS: Single and double infection of SRBSDV and RRSV were obtained with the viruliferous white-backed planthopper and brown planthopper inoculation on four-leaf stage rice seedlings, respectively, under experimental condition. The second upper leaf from each inoculated rice plants were collected at 9, 15, and 20 days post inoculation (dpi) and used for relative quantification of 13 SRBSDV genes and 11 RRSV genes by the reverse-transcription quantitative PCR. Viral gene expression levels were compared between singly and doubly infected samples at the same stage. RESULTS: The movement protein and viroplasm matrix-related genes as well as the structural (capsid) protein genes of both viruses were remarkably up-regulated at different time points in the co-infected rice plants compared with the samples singly infected with SRBSDV or RRSV, however, the RNA silencing suppressor (P6) of only RRSV, but not of both the viruses, was up-regulated. CONCLUSIONS: The SRBSDV-RRSV synergism promoted replication and movement of both viruses and inhibited the host immunity by enhancing the gene suppressing effect exerted by one of them (RRSV).

Characteristics of siRNAs derived from Southern rice black-streaked dwarf virus in infected rice and their potential role in host gene regulation.

BACKGROUND: Virus-derived siRNAs (vsiRNAs)-mediated RNA silencing plays important roles in interaction between plant viruses and their hosts. Southern rice black-streaked dwarf virus (SRBSDV) is a newly emerged devastating rice reovirus with ten dsRNA genomic segments. The characteristics of SRBSDV-derived siRNAs and their biological implications in SRBSDV-rice interaction remain unexplored. METHODS: VsiRNAs profiling from SRBSDV-infected rice samples was done via small RNA deep sequencing. The putative rice targets of abundantly expressed vsiRNAs were bioinformatically predicted and subjected to functional annotation. Differential expression analysis of rice targets and RNA silencing components between infected and healthy samples was done using RT-qPCR. RESULTS: The vsiRNA was barely detectable at 14 days post infection (dpi) but abundantly present along with elevated expression level of the viral genome at 28 dpi. From the 28-dpi sample, 70,878 reads of 18 ~ 30-nt vsiRNAs were recognized (which mostly were 21-nt and 22-nt), covering 75 ~ 91% of the length of the ten genomic segments respectively. 86% of the vsiRNAs had a <50% GC content and 79% of them were 5'-uridylated or adenylated. The production of vsiRNAs had no strand polarity but varied among segment origins. Each segment had a few hotspot regions where vsiRNAs of high abundance were produced. 151 most abundant vsiRNAs were predicted to target 844 rice genes, including several types of host resistance or pathogenesis related genes encoding F-box/LRR proteins, receptor-like protein kinases, universal stress proteins, tobamovirus multiplication proteins, and RNA silencing components OsDCL2a and OsAGO17 respectively, some of which showed down regulation in infected plants in RT-qPCR. GO and KEGG classification showed that a majority of the predicted targets were related to cell parts and cellular processes and involved in carbohydrate metabolism, translation, and signal transduction. The silencing component genes OsDCL2a, OsDCL2b, OsDCL4, and OsAGO18 were down regulated, while OsAGO1d, OsAGO2, OsRDR1 and OsRDR6 were up regulated, significantly, upon SRBSDV infection. CONCLUSIONS: SRBSDV can regulate the expression of rice RNA silencing pathway components and the virus might compromise host defense and influence host pathogenesis via siRNA pathways.

The speed of tubule formation of two fijiviruses corresponds with their dissemination efficiency in their insect vectors.

BACKGROUND: Rice black-streaked dwarf virus (RBSDV) and Southern rice black-streaked dwarf virus (SRBSDV) are two closely related fijiviruses transmitted by the small brown planthopper (SBPH) and white-backed planthopper (WBPH), respectively. SRBSDV has a latent period 4 days shorter than that of RBSDV, implying a more efficient spread in insect vector. Currently, the mechanisms underlying this higher efficiency are poorly understood. However, our recent studies have implicated a role of virus induced tubular structures in the dissemination of fijiiruses within their insect vectors. METHODS: Immunofluorescence labeling was performed to visualize and compare the dynamics of P7-1 tubule formation of the RBSDV and SRBSDV in their own vector insects and nonhost Spodoptera frugiperda (Sf9) cells. RESULTS: Tubule formation of SRBSDV P7-1 was faster than that of RBSDV P7-1. For RBSDV, P7-1 formed tubules were observed at 3-days post-first access to diseased plants (padp) in SBPH. For SRBSDV, these structures were detected as early as 1 day padp in WBPH. Importantly, similar phenomena were observed when P7-1 proteins from the two viruses were expressed alone in Sf9 cells. CONCLUSIONS: Our research revealed a relationship between the speed of P7-1 tubule formation and virus dissemination efficiency and also supports a role of such tubular structures in the spread of reoviruses within insect vectors.

Low Temperature Storage of Southern Rice Black-Streaked Dwarf Virus-Infected Rice Plants Cannot Sustain Virus Transmission by the Vector.

Southern rice black-streaked dwarf virus (SRBSDV) is a novel virus transmitted by white-backed planthopper Sogatella furcifera (Hováth) (Hemiptera: Delphacidae). Due to low virus transmission efficiency by the planthopper, researchers are frequently confronted with shortage of viruliferous vectors or infected rice plants, especially in winter and the following spring. To find new ways to maintain virus-infected materials, viral rice plants were stored at -80°C for 45 or 140 d and evaluated as virus sources in virus transmission by the vector. SRBSDV virions were not degraded during storage at -80°C as indicated by reverse transcription-polymerase chain reaction and reverse transcription real-time PCR detection. The planthopper nymphs fed on the infected thawed plants for 48 h survived at about 40% and showed positive detection of SRBSDV, but they lost the virus after feeding for another 20 d (the circulative transmission period) on noninfected plants. Transmission electron microscope images indicated broken capsid of virions in infected thawed leaves in contrast to integrity capsid of virions in infected fresh leaves. These results show that low temperature storage of SRBSDV-infected rice plants cannot sustain virus transmission by white-backed planthopper.

Relation Between the Viral Load Accumulation of Southern Rice Black-Streaked Dwarf Virus and the Different Developmental Stages of Sogatella furcifera (Hemiptera: Delphacidae).

The white-backed planthopper, Sogatella furcifera (Horvath), is currently the only confirmed vector of Southern rice black-streaked dwarf virus (SRBSDV), which causes severe rice production losses in China. In this study, an absolute quantification qPCR method was used to detect viral gene mRNA expression levels at different developmental stages of white-backed planthoppers fed SRBSDV-infected rice plants. A comparison of viral copy numbers of the SRBSDV S10 gene at the same developmental stage indicated that the white-backed planthopper had higher viral copy numbers when the virus was acquired at the earlier developmental stages. The adult-stage white-backed planthoppers that had acquired the virus at the first-second nymphal stage displayed significantly higher viral titers than white-backed planthoppers that acquired the virus at the third-fourth nymphal stage, at the fifth nymphal stage, and at the adult stage. The fifth nymphal stage white-backed planthoppers that acquired the virus at the first-second nymphal stage displayed higher viral copy numbers than fifth nymphal stage white-backed planthoppers that acquired the virus at the third-fourth nymphal stage and at the fifth nymphal stage. The highest viral load value appeared in the middle adult stage. The annual immigration characteristics of white-backed planthoppers would be beneficial for the dispersal of SRBSDV because this virus could be transmitted far away following the migration of vigorous planthoppers. Therefore, investigating the change in the viral load at different life stages of SRBSDV-positive individuals is required to develop more effective control of the spread of SRBSDV in the field.

Interactive Effects of Southern Rice Black-Streaked Dwarf Virus Infection of Host Plant and Vector on Performance of the Vector, Sogatella furcifera (Homoptera: Delphacidae).

Performance of insect vectors can be influenced by the viruses they transmit, either directly by infection of the vectors or indirectly via infection of the host plants. Southern rice black-streaked dwarf virus (SRBSDV) is a propagative virus transmitted by the white-backed planthopper, Sogatella furcifera (Hovath). To elucidate the influence of SRBSDV on the performance of white-backed planthopper, life parameters of viruliferous and nonviruliferous white-backed planthopper fed rice seedlings infected or noninfected with SRBSDV were measured using a factorial design. Regardless of the infection status of the rice plant host, viruliferous white-backed planthopper nymphs took longer to develop from nymph to adult than did nonviruliferous nymphs. Viruliferous white-backed planthopper females deposited fewer eggs than nonviruliferous females and both viruliferous and nonviruliferous white-backed planthopper females laid fewer eggs on infected than on noninfected plants. Longevity of white-backed planthopper females was also affected by the infection status of the rice plant and white-backed planthopper. Nonviruliferous white-backed planthopper females that fed on infected rice plants lived longer than the other three treatment groups. These results indicate that the performance of white-backed planthopper is affected by SRBSDV either directly (by infection of white-backed planthopper) or indirectly (by infection of rice plant). The extended development of viruliferous nymphs and the prolonged life span of nonviruliferous adults on infected plants may increase their likelihood of transmitting virus, which would increase virus spread.

Sublethal concentrations of pymetrozine reduce Sogatella furcifera transmission of Southern rice black-streaked dwarf virus.

BACKGROUND: The transmission of plant viruses is closely associated with the specific probing behaviors of the vectors. Pymetrozine is a pyridine azomethine insecticide that interferes with nervous regulation of feeding behavior of piercing-sucking insects. This study aimed to evaluate the potential of sublethal concentrations of pymetrozine in reducing the transmission of Southern rice black-streaked dwarf virus (SRBSDV) by the planthopper Sogatella furcifera. RESULTS: Laboratory assays showed that both acquisition and inoculation rates of SRBSDV decreased significantly in the planthoppers feeding on plants treated with lethal concentrations 10% and 50% (LC10 and LC50 ) pymetrozine compared with the insects feeding on the control plants, for which significant effects of pymetrozine concentration and time post-treatment were detected. Honeydew excretion of the planthoppers showed significant reduction with increasing concentration of the insecticide but no significant association with time post-treatment. Electrical penetration graph recordings revealed that total durations of each waveform in both acquisition and inoculation were significantly affected by pymetrozine treatment, with total durations of non-probing (NP), penetration initiation (N1), and extracellular activity (N3) elongated whereas those of salivation (N2) and phloem-related activities (N4-a and N4-b) shortened. Additionally, both acquisition and inoculation rates were significantly lower at 168 h than at 6 h post-treatment. CONCLUSION: The results indicate that sublethal concentrations of pymetrozine reduce SRBSDV transmission, which is associated with reduction in feeding and alteration in probing behaviors characterized by the prolonged non-probing, penetration initiation and extracellular activity and shortened salivation and phloem-related activities. © 2023 Society of Chemical Industry.

Dynamic gene expression of southern rice black-streaked dwarf virus during its infection in rice plants and vector insects.

In this century, a disease caused by southern rice black-streaked dwarf virus (SRBSDV) has resulted in significant loss in rice production in Asia. Aside from infecting rice plants, SRBSDV is transmitted by white-backed planthopper (WBPH) in a persistent propagative manner. Recent studies showed that SRBSDV can dynamically modulate the host cells throughout the infection progress. However, the expression dynamics of the SRBSDV genes during infection remain unclear. Here we established an absolute real-time quantitative PCR method to assess the dynamic of the SRBSDV genes expression in rice plants and planthoppers. Apart from displaying the expression levels of viral genes, we discovered that the expression level of viral genes in insects significantly surpasses that in plant cells. In addition, we identified two nonstructural proteins with unknown functions that exhibit the highest expression levels in plant and insect cells, respectively, which provide possible targets for restraining the disease outbreaks.

Rice varietal resistance to the vector Sogatella furcifera hinders transmission of Southern rice black-streaked dwarf virus.

BACKGROUND: The Southern rice black-streaked dwarf virus (SRBSDV) transmitted by Sogatella furcifera constitutes a threat to sustainable rice production. However, most rice varieties are highly vulnerable to SRBSDV, whereas the occurrence of the viral disease varies significantly under field conditions. This study aimed to evaluate the potential of rice varietal resistance to S. furcifera in reducing SRBSDV transmission. RESULTS: Among the five rice varieties, Zhongzheyou8 and Deyou108 exhibited high resistance to S. furcifera, Baixiangnuo33 was susceptible, and TN1 and Diantun502 were highly susceptible. The S. furcifera generally showed non-preference for and low feeding on the Zhongzheyou8 and Deyou108 plants, which may explain the resistance of these varieties to S. furcifera. Transmission of SRBSDV by S. furcifera was significantly impaired on the resistant varieties, both inoculation and acquisition rates were much lower on Zhongzheyou8 than on TN1. The short durations of S. furcifera salivation and phloem-related activities and the low S. furcifera feeding amount may explain the reduced SRBSDV inoculation and acquisition rates associated with Zhongzheyou8. Spearman's rank correlation revealed a significant negative correlation between S. furcifera resistance and SRBSDV transmission among the tested varieties. CONCLUSION: The results indicate that rice varietal resistance to the vector S. furcifera hinders SRBSDV transmission, which is largely associated with the host plant selection and feeding behaviors of the vector. The current findings shed light on the management of the SRBSDV viral disease through incorporation of S. furcifera resistant rice varieties in the management protocol. © 2024 Society of Chemical Industry.

A virus induces alterations in root morphology while exerting minimal effects on the rhizosphere and endosphere microorganisms in rice.

The highly destructive southern rice black-streaked dwarf virus (SRBSDV) causes significant losses in rice production. To understand its impact on rice root, we studied fibrous root development and root microbiota variation (rhizosphere and endosphere) after SRBSDV infection. SRBSDV infection reduced the number and length of fibrous roots in rice. Interestingly, the rhizosphere had higher bacterial diversity and abundance at the initial (0 days) and 30-day postinfection stages, while 30-day-old roots showed increased diversity and abundance. However, there were no significant differences in microbiota diversity between infected and noninfected rice plants. The major rhizosphere microbiota included Proteobacteria, Bacteroidota, Acidobacteriota, and Planctomycetota, comprising about 80% of the community. The endosphere was dominated by Proteobacteria and Cyanobacteria, constituting over 90%, with Bacteroidota as the next most prominent group. Further, we identified differentially expressed genes related to plant-pathogen interactions, plant hormone signal, and ABC transporters, potentially affecting root morphology. Notably, specific bacteria (e.g. Inquilinus and Actinoplanes) showed correlations with these pathways. In conclusion, SRBSDV primarily influences root growth through host metabolism, rather than exerting direct effects on the root microbiota. These insights into the interactions among the pathogen, rice plant, and associated microbiota could have implications for managing SRBSDV's detrimental effects on rice production.

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 Rice Receptor-like Protein Negatively Regulates Rice Resistance to Southern Rice Black-Streaked Dwarf Virus Infection.

Plants rely on various receptor-like proteins and receptor-like kinases to recognize and defend against invading pathogens. However, research on the role of receptor-like proteins in plant antiviral defense, particularly in rice-virus interactions, is limited. In this study, we identified a receptor-like gene, OsBAP1, which was significantly induced upon infection with southern rice black-streaked dwarf virus (SRBSDV) infection. A viral inoculation assay showed that the OsBAP1 knockout mutant exhibited enhanced resistance to SRBSDV infection, indicating that OsBAP1 plays a negatively regulated role in rice resistance to viral infection. Transcriptome analysis revealed that the genes involved in plant-pathogen interactions, plant hormone signal transduction, oxidation-reduction reactions, and protein phosphorylation pathways were significantly enriched in OsBAP1 mutant plants (osbap1-cas). Quantitative real-time PCR (RT-qPCR) analysis further demonstrated that some defense-related genes were significantly induced during SRBSDV infection in osbap1-cas mutants. Our findings provide new insights into the role of receptor-like proteins in plant immune signaling pathways, and demonstrate that OsBAP1 negatively regulates rice resistance to SRBSDV infection.

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

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.

Silencing the Autophagy-Related Genes ATG3 and ATG9 Promotes SRBSDV Propagation and Transmission in Sogatella furcifera.

Autophagy plays diverse roles in the interaction among pathogen, vector, and host. In the plant virus and insect vector system, autophagy can be an antiviral/pro-viral factor to suppress/promote virus propagation and transmission. Here, we report the antiviral role of autophagy-related genes ATG3 and ATG9 in the white-backed planthopper (Sogatella furcifera) during the process of transmitting the southern rice black-streaked dwarf virus (SRBSDV). In this study, we annotated two autophagy-related genes, SfATG3 and SfATG9, from the female S. furcifera transcriptome. The cDNA of SfATG3 and SfATG9 comprised an open reading frame (ORF) of 999 bp and 2295 bp that encodes a protein of 332 and 764 amino acid residues, respectively. SfATG3 has two conserved domains and SfATG9 has one conserved domain. In S. furcifera females exposed to SRBSDV, expression of autophagy-related genes was significantly activated and shared similar temporal patterns to those of SRBSDV S9-1 and S10, all peaking at 4 d post viral exposure. Silencing the expression of SfATG3 and SfATG9 promoted SRBSDV propagation and transmission. This study provides evidence for the first time that S. furcifera autophagy-related genes ATG3 and ATG9 play an antiviral role to suppress SRBSDV propagation and transmission.

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.