Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 28, 2009
Publication Date: February 23, 2009
Citation: Stenger, D.C., Sisterson, M.S., Krugner, R., Backus, E.A., Hunter, W.B. 2009. A New Phytoreovirus Infecting the Glassy-Winged Sharpshooter (Homalodisca vitripennis). Virology. 386:469-477. Interpretive Summary: The glassy-winged sharpshooter (GWSS) is an invasive insect of economic concern due to its ability to transmit the causal agent of Pierce’s disease. Epidemics of Pierce’s disease occurred in California where large populations of GWSS in citrus subsequently moved into neighboring vineyards. These circumstances prompted research efforts to discover biological agents suitable for control of GWSS populations to mitigate losses associated with Pierce’s disease. Most research on GWSS biological control has focused on parasitoid wasps. Whether viruses infecting GWSS may be suitable for use as biological control agents has received much less attention. A new virus species (designated Homalodisca vitripennis reovirus, HoVRV) infecting GWSS was isolated and characterized. HoVRV was similar in particle structure and genome complement to phytoreoviruses. Complete nucleotide sequences were determined for the 12 double-stranded RNA segments of the HoVRV genome. Sequence comparisons indicated that HoVRV was a novel virus species of the genus Phytoreovirus and most closely related to Rice dwarf virus. HoVRV was detected in GWSS populations of California, the Carolinas, and Texas. HoVRV was present in GWSS salivary gland cells and accumulated to high concentration in individual insects. Virulence of HoVRV towards GWSS does not appear sufficient for use as a biological control agent; nonetheless, sequence variation of HoVRV among different GWSS populations may have utility with respect to tracking GWSS invasion routes.
Technical Abstract: A new virus species of the genus Phytoreovirus was isolated from glassy-winged sharpshooter (GWSS), Homalodisca vitripennis Germar (Hemiptera: Cicadellidae), in California and designated here as Homalodisca vitripennis reovirus (HoVRV). Extraction of nucleic acid from GWSS adults collected from three Californian populations revealed an array of double-stranded (ds) RNA species that were soluble in 2M LiCl and resistant to degradation upon exposure to S1 nuclease and DNase. Analysis of nucleic acid samples from single GWSS adults indicated that HoVRV dsRNA accumulated to high titer in individual insects. Double-shelled isometric virus particles (~53 nm) purified from GWSS adults resembled those observed in thin sections of GWSS salivary glands by transmission electron microscopy. Purified HoVRV virions contained 12 dsRNA segments that, based on complete nucleotide sequences, ranged in size from 4,475 to 1,040 bp. Sequence comparisons indicated that the HoVRV dsRNA segments were most closely related (58.5 to 43.7% nt sequence identity) to the corresponding genome segments of Rice dwarf virus (RDV). Each HoVRV dsRNA segment encoded a single open reading frame (>300 nts) except for segment 11, which appears to be dicistronic. Terminal nucleotide sequences of HoVRV positive-sense RNAs were similar to other phytoreoviruses (GGCG or GGCA at the 5’-end and UGAU or CGAU at the 3’-end) with adjacent imperfect inverted repeats potentially able to base pair. Phylogenetic analyses of the RNA-directed RNA polymerase (encoded by segment 1) and the outer capsid protein (encoded by segment 8) confirmed placement of HoVRV as a species of the genus Phytoreovirus sharing a most recent common ancestor with RDV. Reverse transcription-polymerase chain reaction assays revealed that HoVRV infection of GWSS in California was common and that the virus also occurred in GWSS populations from the Carolinas and Texas.