BackgroundThe transmission of plant viruses by arthropod vectors is closely related to feeding behavior. For persistently transmitted viruses, virus release means that virus moves through the salivary gland microvillus barriers of insects into plant via the stylet. However, whether virus release is dependent on plant tissue and component recognition by the stylet is unclear.ResultsIn this study, the small brown planthopper (SBPH) and two rice viruses transmitted by it were used as a model to explore this question. After the viruliferous insects penetrated a stretched membrane without plant tissue structure and ingested liquid food (rice sap, nutrient solution or water), both viruses were detected in the liquid food after only a 6 min inoculation access period, suggesting that the viruses were released from SBPH salivary gland independent of plant tissue and component recognition by the stylet. In subsequent electrical penetration graph (EPG) analysis, N4a‐like and N4b‐like waveforms, similar to N4a (phloem salivation before ingestion) and N4b (sieve element ingestion), were observed during SBPH penetrating the membrane, exhibiting normal feeding activity of planthopper on membrane, which further demonstrated that virus release from salivary gland was along with feeding activity, without the stylet sensing plant tissue. EPG analysis and identification of salivary proteins indicated more active feeding behavior and efficient salivation in viruliferous planthoppers.ConclusionThese results suggest that the rice virus is released from insect salivary gland independent of plant tissue and component recognition by the stylet, and the simple virus release mode facilitates virus transmission by vectors. © 2020 Society of Chemical Industry

BACKGROUND: Plant viruses transmitted by arthropod vectors threaten crop health worldwide. Rice stripe virus (RSV) is one of the most important rice viruses in East Asia and is transmitted by the small brown planthopper (SBPH). Previously, it was demonstrated that the viral glycoprotein NSvs2-N could mediate RSV infection of the vector midgut. Therefore, NSvc2-N protein could potentially be used to reduce RSV transmission by competitively blocking midgut receptors.RESULTS: Here, we report that transgenic rice plants expressing viral glycoprotein can interfere with RSV acquisition and transmission by SBPH. The soluble fraction (30-268 amino acids, designated NSvs2-N S ) of NSvs2-N was transformed into rice calli, which produced plants harboring the exogenous gene. When SBPH was fed on transgenic plants prior to RSV-infected rice (sequential feeding) and when insects were fed on RSV-infected transgenic plants (concomitant feeding), virus acquisition by the insect vector was inhibited, and subsequent viral titers were reduced. Immunofluorescence labeling also indicated that viral infection of the insect midgut was inhibited after SBPH was fed on transgenic plants. The system by which RSV infected insect cells in vitro was used to corroborate the role of NSvc2-N S in reducing viral infection. After the cells were incubated with transgenic rice sap, the virus infection rate of the cells decreased significantly, and viral accumulation in the cells was lower than that in the control group.CONCLUSION: These results demonstrated the negative effect of NSvs2-N S transgenic plants on RSV transmission by insect vectors, which provides a novel and effective way to control plant viral diseases.

Rice viral diseases adversely affect crop yield and quality. Most rice viruses are transmitted through insect vectors. However, the traditional whole-plant inoculation method cannot control the initial inoculation site in rice plants because the insect feeding sites in plants are random. To solve this problem, we established a determined-part inoculation approach in this study that restricted the insect feeding sites to specific parts of the rice plant. Rice stripe virus (RSV) was used as the model virus and was inoculated at the bottom of the stem using our method. Quantitative real-time PCR and Western blot analyses detected RSV only present at the bottom of the Nipponbare (NPB) stem at 1 day post-inoculation (dpi), indicating that our method successfully controlled the inoculation site. With time, RSV gradually moved from the bottom of the stem to the leaf in NPB rice plants, indicating that systemic viral spread can also be monitored using this method. In addition, a cultivar resistant to RSV, Zhendao 88 (ZD88), was inoculated using this method. We found that RSV accumulation in ZD88 was significantly lower than in NPB. Additionally, the expression level of the resistant gene STV11 in ZD88 was highly induced at the initial invasion stage of RSV (1 dpi) at the inoculation site, whereas it remained relatively stable at non-inoculated sites. This finding indicated that STV11 directly responded to RSV invasion to inhibit virus accumulation at the invasion site. We also proved that this approach is suitable for other rice viruses, such as Rice black-streaked dwarf virus (RBSDV). Interestingly, we determined that systemic infection with RSV was faster than that with RBSDV in NPB, which was consistent with findings in field trails. In summary, this approach is suitable for characterizing the viral infection process in rice plants, comparing the local viral accumulation and spread among different cultivars, analyzing the spatiotemporal expression pattern of resistance-associated genes, and monitoring the infection rate for different viruses.