Background: Rice stripe virus (RSV), which is transmitted by small brown planthopper (Laodelphax striatellus Fallén, SBPH), has been reported to be epidemic and cause severe rice stripe disease in rice fields in many East Asian countries, including China. Investigation on viral localization in the vector is very important for elucidating transmission mechanisms of RSV by SBPH. In this study, transmission electron microscopy and immuno-gold labeling technique were used to investigate the subcellular localization of the ribonucleoproteins (RNPs) of RSV in the digestive tract, muscles, ovary and testes of SBPH.
Results: A lot of amorphous RSV inclusion bodies with high electron density were observed in the cytoplasmic matrix and vacuoles of follicular cells of ovarioles in viruliferous SBPH, which were very similar to viral inclusions formed in rice cells. After magnified, it was found that sand-like or parallel filamentary structures were constructed inside the electron-dense inclusions. A large numbers of RSV RNPs distributed diffusely throughout the eggshell surface and interior of ovum, midgut lumen and epithelial cells, while the amount of the virus in muscles was far less than that in the ovary and midgut tissues. Besides RSV, numerous endogenous microorganisms were also observed in SBPH body, including yeast-like endosymbiotes (YLES), endosymbiotic bacteria and insect virus.
Conclusions: According to the results of the virus localization, a potential mechanism of RSV transovarial transmission was proposed that RSV might replicate and accumulate initially in the inclusions of follicular cells, then exploit the pathway of the nutrition transportation to pass through the eggshell and spread into the oocytes along with the nutrition. Moreover, RSV might exploit muscles for its spread in vector body with a lower efficiency.