Study On Transovarial Transmission Of Rice Gall Dwarf Virus In Its Vector Recilia Dorsalis

Recently, Rice gall dwarf disease caused by Rice gall dwarf virus (RGDV) has prevailed in Guangdong province of China. RGDV, a member of Phytoreovirus in the family of Reoviridae, is mainly transmitted by Recilia dorsalis with a persistent-propagative manner. Currently, sientists have studied the occurrence, damages, disease symptoms, genome structures and functions of RGDV. However, whether RGDV is transovarial transmission in R. dorsalis remains controversial. There was no report about the infection process of RGDV in ovaries of its vectors R. dorsalis.In this study, we verified that RGDV is transovarial transmission in R. dorsalis by RT-PCR technology. To avoid infection by viruliferous female R. dorsalis, we picked the eggs of viruliferous insects to the wet filter paper, immediately transferred hatched-instars individually to health seedling until eclosion. Results showed that rates of viruliferous insects of F1 and F2 generation were 77.3% and 78.9% respectively, preliminary suggesting RGDV could be transovarial transmission by R. dorsalis. To further comfirm how the virus infect the eggs, we treated egg shell of R. dorsalis with the Hyamine reagent with different times. Result of the assay showed that rates of viruliferous eggs treated with the reagent was 75%, which was comparable to that of the control treated with H2O, suggesting that the egg shell was not corelated with the transovarial transmission of RGDV and RGDV infected the eggs before ovipositio The tests of male R. dorsalis and female R. dorsalis mating found that the offspring of the parents between the mating of viruliferous female R. dorsalis and non-viruliferous male R. dorsalis are viruliferous, and the offspring of mating of viruliferous male R. dorsalis and non-viruliferous female R. dorsalis are non-viruliferous. It proved that the infection of offspring merely related with viruliferous female, and nothing to do with whether the male R. dorsalis is viruliferous. In addition, the non-viruliferous parent, mating with viruliferous parent, could be non-viruliferous, i.e. RGDV could not be transmitted horizontally among R. dorsalis.To trace the infection course of RGDV, we immunolabeled the reproductive organ of viruliferous R. dorsalis at different days post eclosion with RGDV-rhodamine, the result of the assay showed that RGDV firstly infected the terminal filament, the pedicel and the oviduct at 1-2 days post eclosion of R. dorsalis, then they infected the germarium at 3-4 days post eclosion and spread to the whole germarium at 5-6 days post eclosion, subsequently the RGDV spread successively to the growing zone and the vitellogenesis area at 7-8 and 9-10 days post eclosion respectively. This finding provides a new light of the infection course of RGDV in the ovary of insect vector, R. dorsalis.RGDV, which was tranmited in a persistent-propagative manner, propagated highly efficiently in its insect vector R. dorsalis. Evidences have shown that RGDV spread to adjacent cells by tubular structure induced by RGDV encoded Pns11. So we immunolabeled Pns11 in the ovary of R. dorsalis to explore the spread course of RGDV in the ovary. The result of the assay showed that RGDV spread from the follicular cell of the germarium, where they replicated intensively, to the oocyte by the tubular structure of Pns11. In addition, RGDV also spread along with the microvilli of the vitellogenesis area, which was between the the follicular cell and vitelline membrane, to the oocyte by the tubular structure of Pns11. The result was further comfirmed by the transmission electron microscopy of the ovary.In summary, We demonstrated that RGDV could be transovarial transmission by its insect vector R.dorsalis by RT-PCR technology and immunofluorescence assay. We also illustrated the infection course of RGDV in the ovaries R. dorsalis and tubular structure of Pnsl 1 participated in the spread of the RGDV in R. dorsalis ovaries. This study will lay the foundations for the future to further study the mechanism of understanding of transovarial transmission of insect vector and pave the way to design new strategies to control virus transmission.