Southern Rice Black-streaked Dwarf Virus Research Articles

Climate change shocks and crop production: The foodgrain bowl of India as an example

Global warming is causing climate change (CC) characterized by increased frequency of heatwaves, droughts, erratic rains, hailstorms, cloudbursts, floods, landslides etc. The CC has already adversely affected ecosystems. In spite of efforts to mitigate greenhouse gas (GHG) emissions, which lead to warming, the global temperature during 2011–20 was 1.1°C above that during pre-industrial era. The projections are that warming will continue to increase and adverse effects will intensify particularly in developing countries like India. In India a number of studies have recorded wide spatial variability in rainfall, though, many reported a general overall negative trend since mid-20th century. Further, varying pattern of rainfall has been recorded in three agroclimatic regions of Punjab state, the granary of India. Unseasonal rains followed by spiked temperature during winter (rabi) season of 2021–22 reduced wheat (Triticum aestivum L.) yield in Punjab by 651 kg/ha and by 301 kg/ha in Haryana compared to 2020–21. Further, the grain was of lower quality. During rainy (kharif) season of 2022, Southern Rice Black-streaked Dwarf Virus (SRBSDV), appeared for the first time in Punjab and Haryana. Some farmers ploughed the affected fields. Adverse weather during rabi 2022–23 also, reduced the wheat yield (143–150 kg/ha) in these states. At the national level, erratic weather during rabi 2021–22 and kharif 2022 caused losses of about 3 mt of grain of each of wheat and rice (Oryza sativa L.). The projected increased adverse effects due to intensified CC include food insecurity. Thus, there is an emergent need to accelerate implementation of adaptation and mitigation strategies in agriculture. The adaptation options include cultivar improvement, conservation agriculture altering growing seasons, crop diversification and sustainable soil, and water resource management. In the process of adaptive management of crop production, adjusting sowing dates and breeding cultivars having varying duration in consonance with CC has been one of the central aspects. Shifting sowing dates to find appropriate crop cultivation season is a low-cost measure. However, cultivar development is time and resource consuming. Novel biotechnological tools enable fast cultivar development with precision, and facilitate mobilization of genes from wild-weedy relatives, which are rich in genes conferring resistance/tolerance to biotic and biotic stresses, required to combat CC challenge. In view of CC stress on water resources, improving water-use efficiency (WUE) has gained importance. Sensor-based micro-irrigation/fertigation has great potential to enhance water and fertilizer-use efficiency. Similarly, the application of other smart technologies like nanotechnology, sensor-based pesticide application, bio-fertilizers and bio-pesticides, need to be mobilised. In view of agro-ecological diversity in India, right-sized regionspecific technology packages have to be developed implying that crop research will expand exponentially. This needs strengthening of human resources and institutional infrastructure, expanding and linking basic and applied researches, and fortifying inter-disciplinary/inter-institutional collaborations to develop and diffuse technology innovations. Enabling factors include enhanced funding and international cooperation. All-out efforts are needed to have more climate-resilient agriculture.

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

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. 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. 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.

Introgression of OsAP47 by marker-assisted selection enhanced resistance against southern rice black-streaked dwarf virus disease

Southern rice black-streaked dwarf virus disease (SRBSDVD) is the most destructive viral disease in rice. In order to breeding resistant cultivars, Insertion-Deletion (InDel) markers were developed linked to OsAP47, the first isolated major resistance gene against SRBSDVD. Marker-assisted selection (MAS) was conducted to introduce this gene into the commercial variety. A rice line carrying homozygous resistance allele of OsAP47 was selected and named Kanghei No. 201 (KH201). Evaluated by artificial inoculation, KH201 showed significantly higher resistance than the recurrent parent Suxiu No.867 (SX867). And no significant differences were detected for KH201 in the yield-related components, including spikelets per panicle (SPP), ripened grains per panicle (RGPP), 1000-grain weight (TGW) and panicles per square meter (PPSM), leading to stable theoretical yield. The results indicated that introgression of OsAP47 improved rice resistance and can avoid yield losses produced by SRBSDVD. KH201 was demonstrated as a resistance material that could be used in rice breeding.

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

The damage caused by white-back planthopper (WBPH, Sogatella furcifera) and brown planthopper (BPH, Nilaparvata lugens), as well as southern rice black-streaked dwarf virus (SRBSDV), considerably decreases 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 (SSST) method, insect quantification was further conducted at the end of 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. RHT and HN12-239 were moderately resistant to SRBSDV. In addition, we found that WBPH did not penetrate stems with stylets, but did more probing bouts and then xylem sap ingestion when feeding on HN12-239 than the susceptible control rice TN1. 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.

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.

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

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. 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. 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.

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 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.

CRISPR/Cas9-mediated gene editing of vacuolar ATPase subunit d mediates phytohormone biosynthesis and virus resistance in rice.

Vacuolar ATPases (V-ATPases) are proton pumps for proton translocation across membranes that utilize energy derived from ATP hydrolysis; OsV-ATPase subunit d (OsV-ATPase d) is part of an integral, membrane-embedded V0 complex in the V-ATPase complex. Whether OsV-ATPase d is involved in phytohormone biosynthesis and resistance in rice remains unknown. The knockout mutants of OsV-ATPase d in rice were generated using the CRISPR/Cas9 system, and mutation of OsV-ATPase d did not show any detrimental effect on plant growth or yield productivity. Transcriptomic results showed that OsV-ATPase d is probably involved in mediating the biosynthesis of plant hormones and resistance in rice. Compared to wild type, mutation of OsV-ATPase d significantly increased JA and ABA biosynthesis and resistance against Southern rice black-streaked dwarf virus (SRBSDV), but it decreased resistance against Rice stripe virus (RSV) in rice. The data presented in this study reveal that OsV-ATPase d mediates phytohormone biosynthesis and virus resistance in rice and can be selected as a potential target for resistance breeding in rice.

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.

A fijiviral nonstructural protein triggers cell death in plant and bacterial cells via its transmembrane domain.

Southern rice black-streaked dwarf virus (SRBSDV; Fijivirus, Reoviridae) has become a threat to cereal production in East Asia in recent years. Our previous cytopathologic studies have suggested that SRBSDV induces a process resembling programmed cell death in infected tissues that results in distinctive growth abnormalities. The viral product responsible for the cell death, however, remains unknown. Here P9-2 protein, but not its RNA, was shown to induce cell death in Escherichia coli and plant cells when expressed either locally with a transient expression vector or systemically using a heterologous virus. Both computer prediction and fluorescent assays indicated that the viral nonstructural protein was targeted to the plasma membrane (PM) and further modification of its subcellular localization abolished its ability to induce cell death, indicating that its PM localization was required for the cell death induction. P9-2 was predicted to harbour two transmembrane helices within its central hydrophobic domain. A series of mutation assays further showed that its central transmembrane hydrophobic domain was crucial for cell death induction and that its conserved F90, Y101, and L103 amino acid residues could play synergistic roles in maintaining its ability to induce cell death. Its homologues in other fijiviruses also induced cell death in plant and bacterial cells, implying that the fijiviral nonstructural protein may trigger cell death by targeting conserved cellular factors or via a highly conserved mechanism.

A Review of Vector-Borne Rice Viruses.

Rice (Oryza sativa L.) is one of the major staple foods for global consumption. A major roadblock to global rice production is persistent loss of crops caused by plant diseases, including rice blast, sheath blight, bacterial blight, and particularly various vector-borne rice viral diseases. Since the late 19th century, 19 species of rice viruses have been recorded in rice-producing areas worldwide and cause varying degrees of damage on the rice production. Among them, southern rice black-streaked dwarf virus (SRBSDV) and rice black-streaked dwarf virus (RBSDV) in Asia, rice yellow mottle virus (RYMV) in Africa, and rice stripe necrosis virus (RSNV) in America currently pose serious threats to rice yields. This review systematizes the emergence and damage of rice viral diseases, the symptomatology and transmission biology of rice viruses, the arm races between viruses and rice plants as well as their insect vectors, and the strategies for the prevention and control of rice viral diseases.

Development of a Dot-Elisa Assay for Diagnosis of Southern Rice Black-Streaked Dwarf Disease in the Field

Outbreaks of the Southern rice black-streaked dwarf virus (SRBSDV) have caused significant losses in many rice-growing areas in Vietnam, especially in both North and Central Vietnam in recent years. To detect the virus, traditional reverse transcription polymerase chain reaction (RT-PCR) methodology and immunoassays are currently employed. RT-PCR is accurate but requires expensive chemicals and instruments, as well as complex procedures that limit its applicability for field tests. To develop a cheaper, simpler, and reliable SRBSDV diagnosis assay based on the dot-enzyme-linked immunosorbent assay (dot-ELISA) method, anti-SRBSDV polyclonal antibodies were produced by using the antigens derived from the P10 coat protein of SRBSDV, which was achieved from a previous study. The IgG antibody purified from the antiserum of recombinant P10-immunized mice by protein A-agarose affinity chromatography could specifically detect both the target protein and SRBSDV at a dilution of 1:100000. In the trial test of SRBSDV diagnosis, the dot-ELISA assay using the obtained anti-SRBSDV antibody showed an accuracy rate of 90.9% in comparison with the standard RT-PCR assay. These results are important premises for the large-scale application of dot-ELISA assay for SRBSDV diagnosis in order to protect rice crops against viral disease damage.

A plant nonenveloped double-stranded RNA virus activates and co-opts BNIP3-mediated mitophagy to promote persistent infection in its insect vector

Mitophagy that selectively eliminates damaged mitochondria is an essential mitochondrial quality control mechanism. Recently, mitophagy has been shown to be induced in host cells infected by a few animal viruses. Here, we report that southern rice black-streaked dwarf virus (SRBSDV), a plant nonenveloped double-stranded RNA virus, can also trigger mitophagy in its planthopper vector to prevent mitochondria-dependent apoptosis and promote persistent viral propagation. We find that the fibrillar structures constructed by the nonstructural protein P7-1 of SRBSDV directly target mitochondria via interaction with the mitophagy receptor BNIP3 (BCL2 interacting protein 3), and these mitochondria are then sequestered within autophagosomes to form mitophagosomes. Moreover, SRBSDV infection or P7-1 expression alone can promote BNIP3 dimerization on the mitochondria, and induce autophagy via the P7-1-ATG8 interaction. Furthermore, SRBSDV infection stimulates the phosphorylation of AMP-activated protein kinase (AMPK), resulting in BNIP3 phosphorylation via the AMPKα-BNIP3 interaction. Together, P7-1 induces BNIP3-mediated mitophagy by promoting the formation of phosphorylated BNIP3 dimers on the mitochondria. Silencing of ATG8, BNIP3, or AMPKα significantly reduces virus-induced mitophagy and viral propagation in insect vectors. These data suggest that in planthopper, SRBSDV-induced mitophagosomes are modified to accommodate virions and facilitate persistent viral propagation. In summary, our results demonstrate a previously unappreciated role of a viral protein in the induction of BNIP3-mediated mitophagy by bridging autophagosomes and mitochondria and reveal the functional importance of virus-induced mitophagy in maintaining persistent viral infection in insect vectors.

The Entomopathogenic Fungus Metarhizium anisopliae Affects Feeding Preference of Sogatella furcifera and Its Potential Targets' Identification.

The rice planthopper Sogatella furcifera is a unique vector of the southern rice black-streaked dwarf virus (SRBSDV). The feeding behavior of S. furcifera should directly affect the diffusion of this virus. In this study, we noted that the infection of Metarhizium anisopliae CQMa421 on S. furcifera disturbed the feeding behavior of this pest to SRBSDV-infected rice, from preference to non-preference. Then, we further investigated the potential targets of M. anisopliae CQMa421 on the feeding behavior of S. furcifera after 0 h, 24 h and 48 h of infection by transcriptomic analysis via Illumina deep sequencing. A total of 93.27 GB of data was collected after sequencing, from which 91,125 unigenes were annotated, including 75 newly annotated genes. There were 1380 vs. 2187 and 137 vs. 106 upregulated and downregulated differentially expressed genes (DEGs) detected at 24 h and 48 h, respectively. The biological functions and associated metabolic processes of these genes were determined with the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The results suggested that major of DEGs are involved in energy metabolism, biosynthesis, immune response, the FoxO signaling pathway, the MAPK signaling pathway and apoptosis in response to the fungal infection. Noteworthily, several olfactory-related genes, including odorant receptors and odorant binding proteins, were screened from these differentially expressed genes, which played critical roles in regulating the olfactory behavior of insects. Taken together, these results provide new insights for understanding the molecular mechanisms underlying fungus and host insect interaction, especially for olfactory behavior regulated by fungus.

NF-YA transcription factors suppress jasmonic acid-mediated antiviral defense and facilitate viral infection in rice.

NF-Y transcription factors are known to play many diverse roles in the development and physiological responses of plants but little is known about their role in plant defense. Here, we demonstrate the negative roles of rice NF-YA family genes in antiviral defense against two different plant viruses, Rice stripe virus (RSV, Tenuivirus) and Southern rice black-streaked dwarf virus (SRBSDV, Fijivirus). RSV and SRBSDV both induced the expression of OsNF-YA family genes. Overexpression of OsNF-YAs enhanced rice susceptibility to virus infection, while OsNF-YAs RNAi mutants were more resistant. Transcriptome sequencing showed that the expression of jasmonic acid (JA)-related genes was significantly decreased in plants overexpressing OsNF-YA when they were infected by viruses. qRT-PCR and JA sensitivity assays confirmed that OsNF-YAs play negative roles in regulating the JA pathway. Further experiments showed that OsNF-YAs physically interact with JA signaling transcription factors OsMYC2/3 and interfere with JA signaling by dissociating the OsMYC2/3-OsMED25 complex, which inhibits the transcriptional activation activity of OsMYC2/3. Together, our results reveal that OsNF-YAs broadly inhibit plant antiviral defense by repressing JA signaling pathways, and provide new insight into how OsNF-YAs are directly associated with the JA pathway.

The Dark Septate Endophyte, Phialocephala fortinii J2PC4, Mitigates Southern Rice Black-Streaked Dwarf Disease and Impacts the Mortality of White Back Planthopper

Southern rice black-streaked dwarf disease (SRBSDD), caused by the southern rice black-streaked dwarf virus (SRBSDV) and transmitted by the white-backed planthopper (WBPH), is a severe disease responsible for significant yield losses in Southeast Asia, including China. The present study investigated utilization of dark septate endophyte (DSE) fungi against SRBSDD and WBPHas a new, effective approach for managing this disease. An isolate of the DSE fungus, Phialocephala fortinii J2PC4, was selected based on its effective symbiosis with rice. Phialocephala fortinii J2PC4 significantly promoted the growth of the rice, increasing plant height (14.8%), fresh weight (59.5%), and dry weight (60.5%) relative to the untreated control in growth-promotion experiments. In experiments assessing disease and pest suppression, growth of rice plants P. fortinii J2PC4 also promoted growth, increasing plant height(22.4%), fresh weight (74.0%), and dry mass (32.4%). Plants infested with WBPH for 48 hours exhibited a WBPH mortality rate of 8.2% in P. fortinii J2PC4 treated plants compared to 1.5% in the control plants. Disease incidence of SRBSDD in the plants treated with P. fortinii J2PC4 exhibited a 28.5% reduction in SRBSDD disease incidence compared to control plants. P. fortinii J2PC4 colonization of rice seedlings decreased the malondialdehyde (MDA) content, increased the superoxide dismutase (SOD) and peroxidase (POD) activity in rice leaves and induced the expression of the resistance-related genes, AOS, PR1a, and PR1b. In contrast POX1 and OsSAUR2 were down-regulated, relative to control plants. Larval production by WBPH in P. fortinii J2PC4 treated plants was also 24.7% lower than control plants in the pest resistance experiment. Our results provide new insights on use of the DSE fungus, P. fortinii J2PC4, as a biofertilizer and a biocontrol agent, which can potentially be applied as a new, safe and effective treatments for growth stimulation and disease and pest control in rice plants.

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

Simple SummaryPlant viruses are mostly transmitted by insects and cause severe damage to crops. The southern rice black-streaked dwarf virus is a rice virus exclusively transmitted by a planthopper, Sogatella furcifera. Autophagy is usually initiated as an adaptive response for cell survival in unfavorable conditions, such as pathogen invasion. The invasion of the virus in the vector may elicit autophagy and may subsequently function to suppress or promote virus propagation and transmission in the insect vector. Here, we annotated two key autophagy-related genes, SfATG3 and SfATG9, in the planthopper vector and found that the genes are conserved among various insects. Interestingly, exposure of the vector to the virus activated the expression of SfATG3 and SfATG9, and silencing SfATG3 or SfATG9 promoted propagation and transmission rates of the virus. These results indicate that the expression of autophagy-related genes is initiated in the vector following exposure to the virus and that autophagy-related genes functions to suppress SRBSDV propagation and transmission.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.

A virus-derived small RNA targets the rice transcription factor ROC1 to induce disease-like symptom

Virus-derived small interfering RNAs (vsiRNAs) in plants can target host transcripts to induce symptom development. Southern rice black-streaked dwarf virus (SRBSDV) is the most damaging rice-infecting virus, which causes severe stunting and poorly developed roots in rice plants, thereby posing a serious threat to rice production. In this study, we show that a vsiRNA (vsiR-S9-18), generated from SRBSDV genome segment 9, targets the transcription factor ROC1 in rice. SRBSDV infection triggered the production of vsiR-S9-18 and resulted in the downregulation of ROC1 in rice plants. Transient expression of vsiR-S9-18 in rice protoplasts and tobacco leaves further demonstrated the specific association of vsiR-S9-18 with ROC1. Moreover, the ROC1-knockout rice plants displayed shortened roots, similar to the phenotype of root growth inhibition caused by SRBSDV infection. We propose that vsiR-S9-18 inhibits root elongation via ROC1, which has been proven to regulate root growth. This finding extends our understanding of the role of vsiRNA in viral disease development and is helpful for the development of new antiviral approaches.

Flotillin 2 Facilitates the Infection of a Plant Virus in the Gut of Insect Vector.

ABSTRACTMost plant viruses require insect vectors for transmission. One of the key steps for the transmission of persistent-circulative plant viruses is overcoming the gut barrier to enter epithelial cells. To date, little has been known about viral cofactors in gut epithelial cells of insect vectors. Here, we identified flotillin 2 as a plasma membrane protein that facilitates the infection of rice stripe virus (RSV) in its vector, the small brown planthopper. Flotillin 2 displayed a prominent plasma membrane location in midgut epithelial cells. The nucleocapsid protein of RSV and flotillin 2 colocalized on gut microvilli, and a nanomolar affinity existed between the two proteins. Knockout of flotillin 2 impeded the entry of virions into epithelial cells, resulting in a 57% reduction of RSV levels in planthoppers. The knockout of flotillin 2 decreased disease incidence in rice plants fed by viruliferous planthoppers from 40% to 11.7%. Furthermore, flotillin 2 mediated the infection of southern rice black-streaked dwarf virus in its vector, the white-backed planthopper. This work implies the potential of flotillin 2 as a target for controlling the transmission of rice stripe disease.IMPORTANCE Plant viral diseases are a major threat to world agriculture. The transmission of 80% of plant viruses requires vector insects, and 54% of vector-borne plant viruses are persistent-circulative viruses, which must overcome the barriers of gut cells with the help of proteins on the cell surface. Here, we identified flotillin 2 as a membrane protein that mediates the cell entry of rice stripe virus in its vector insect, small brown planthopper. Flotillin 2 displays a prominent cellular membrane location in midgut cells and can specifically bind to virions. The loss of flotillin 2 impedes the entry of virions into the midgut cells of vector insects and substantially suppresses viral transmission to rice. Therefore, flotillin 2 may be a promising target gene for manipulation in vector insects to control the transmission of rice stripe disease and perhaps that of other rice virus diseases in the future.