Adverse Effects of Rice gall dwarf virus upon its Insect Vector Recilia dorsalis (Hemiptera: Cicadellidae)

Rice gall dwarf virus (RGDV), a plant reovirus that threatens rice production in Southeast Asia and Southern China, is transmitted by the leafhopper vector Recilia dorsalis in a persistent-propagative manner. To assess the direct effects of RGDV on R. dorsalis, we established an infected leafhopper population from eggs laid by viruliferous females using the water-soaked filter paper culture method. Life history parameters indicated that the virus was harmful to its vector in terms of all biotic indices, including reduced survival rate, emergence rate, fecundity, and longevity of adults, compared with a nonviruliferous control population. Those findings were supported by systematic monitoring of viruliferous rates of R. dorsalis in different overwintering generations. To better elucidate the adverse effects of RGDV on its vector, we measured fecundity at the molecular level using quantitative reverse-transcription polymerase chain reaction and Western blot assays, which revealed differential expression of vitellogenin (Vg) in viruliferous versus nonviruliferous adult females. We infer that RGDV reduced levels of Vg transcript and protein product, resulting in the lower fecundity of its vector. Overall, this study demonstrates how RGDV exerts an adverse effect on R. dorsalis, which hinders the expansion of viruliferous populations of the insect.

Viroplasm matrix protein Pns9 from rice gall dwarf virus forms an octameric cylindrical structure

The non-structural Pns9 protein of rice gall dwarf virus (RGDV) accumulates in viroplasm inclusions, which are structures that appear to play an important role in viral morphogenesis and are commonly found in host cells infected by viruses in the family Reoviridae. Immunofluorescence and immunoelectron microscopy of RGDV-infected vector cells in monolayers, using antibodies against Pns9 of RGDV and expression of Pns9 in Spodoptera frugiperda cells, demonstrated that Pns9 is the minimal viral factor necessary for formation of viroplasm inclusion during infection by RGDV. When Pns9 in solution was observed under a conventional electron microscope, it appeared as ring-like aggregates of approximately 100 Å in diameter. Cryo-electron microscopic analysis of these aggregates revealed cylinders of octameric Pns9, whose dimensions were similar to those observed under the conventional electron microscope. Octamerization of Pns9 in solution was confirmed by the results of size-exclusion chromatography. Among proteins of viruses that belong to the family Reoviridae whose three-dimensional structures are available, a matrix protein of the viroplasm of rotavirus, NSP2, forms similar octamers, an observation that suggests similar roles for Pns9 and NSP2 in morphogenesis in animal-infecting and in plant-infecting reoviruses.

Association of Rice Gall Dwarf Virus with Microtubules Is Necessary for Viral Release from Cultured Insect Vector Cells

ABSTRACT Vector insect cells infected with Rice gall dwarf virus, a member of the family Reoviridae, contained the virus-associated microtubules adjacent to the viroplasms, as revealed by transmission electron, electron tomographic, and confocal microscopy. The viroplasms, putative sites of viral replication, contained the nonstructural viral proteins Pns7 and Pns12, as well as core protein P5, of the virus. Microtubule-depolymerizing drugs suppressed the association of viral particles with microtubules and prevented the release of viruses from cells without significantly affecting viral multiplication. Thus, microtubules appear to mediate viral transport within and release of viruses from infected vector cells.