Abstract
Numerous piercing-sucking insects can persistently transmit viral pathogens in combination with saliva to plant phloem in an intermittent pattern. Insect vectors maintain viruliferous for life. However, the reason why insect vectors discontinuously transmit the virus remains unclear. Rice dwarf virus (RDV), a plant reovirus, was found to replicate and assemble the progeny virions in salivary gland cells of the leafhopper vector. We observed that the RDV virions moved into saliva-stored cavities in the salivary glands of leafhopper vectors via an exocytosis-like mechanism, facilitating the viral horizontal transmission to plant hosts during the feeding of leafhoppers. Interestingly, the levels of viral accumulation in the salivary glands of leafhoppers during the transmitting period were significantly lower than those of viruliferous individuals during the intermittent period. A putative viral release threshold, which was close to 1.79 × 104 copies/μg RNA was proposed from the viral titers in the salivary glands of 52 leafhoppers during the intermittent period. Thus, the viral release threshold was hypothesized to mediate the intermittent release of RDV from the salivary gland cells of leafhoppers. We anticipate that viral release threshold-mediated intermittent transmission by insect vectors is the conserved strategy for the epidemic and persistence of vector-borne viruses in nature.
Highlights
Several persistent plant viruses of agricultural importance are transmitted to plants by piercing– sucking insect vectors, such as leafhoppers, planthoppers, and whiteflies (Jia et al, 2018)
To address how Rice dwarf virus (RDV) was released from the cells of salivary gland to overcome the salivary gland release barrier, the accumulation of RDV in the salivary glands was first studied
Immunofluorescence assays showed that at 12 days padp, RDV antigens were localized to the type III-cells (Figure 1C); type II- and III-cells (Figure 1D); type III-cells, type IV-cells, and accessory salivary glands (Figure 1E), or they were found throughout the principal salivary glands (Figure 1F)
Summary
Several persistent plant viruses of agricultural importance are transmitted to plants by piercing– sucking insect vectors, such as leafhoppers, planthoppers, and whiteflies (Jia et al, 2018). These vectors are usually infected with viruses throughout their lifetime, yet they transmit the virus intermittently (Gamez, 1973; Reynaud and Peterschmitt, 1992; Muniyappa et al, 2000; Ammar and Nault, 2002; Pu et al, 2012). The reason why insect vectors intermittently transmit viruses and the association of intermittent transmission with viral infection in the plant hosts remain unknown.
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