Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 2, 2008
Publication Date: July 16, 2008
Citation: Hunter, W.B. 2008. Molecular evidence for three novel viruses in Glassy-winged Sharpshooters, 'Homalidisca vitripennis' (Hemiptera: Cicadellidae). American Society for Virology Meeting. Technical Abstract: A metagenomic approach was used to identify viral pathogens in the glassy-winged sharpshooter, GWSS, Homalodisca vitripennis (=H. coagulata), is renowned as the principal vector of the plant pathogenic bacterium Xylella fastidiosa which causes a number of economically important diseases including Pierce’s disease of grapes. The aim of our research program is to identify and elucidate the properties of viruses that occur naturally in leafhoppers like GWSS, with the intent of developing biorational control agents. As part of this effort, we constructed four cDNA libraries derived from whole insects and midguts. Resultant ESTs led to the discovery of three single-stranded RNA (ssRNA) viruses, denoted Homalodisca coagulata virus-1; H. vitripennis virus 2; and HoVV 3. Genomic RNA from HoCV-1 was constructed by compiling ESTs from two cDNA libraries derived from whole body and midgut-specific tissues respectively. The 5'-terminal sequence was determined by sequencing both strands of 11 overlapping cDNA clones obtained through RACE. Genome organization. HoCV-1 has a dicistronic genome comprised of two ORFs separated by a short intergenic region. The 5'-proximal ORF possesses sequence motifs characteristic of nonstructural proteins (helicase, cysteine protease, RNA-dependent RNA polymerase) while the 3'-proximal ORF shows similarity to structural proteins. Phylogenetic analysis. RdRp motifs I-VIII of the cripaviruses, were compared within the Dicistroviridae, three discrete clusters were formed. The second viral species, HoVV-2, was a contig of 23 ESTs with significant similarity to Sacbrood virus (SBV, 2e-113) with a length of 2,289 nt. Genome organization. HoVV-2 is thought to belong to the genus Iflavirus. Unlike the dicistroviruses, members of the genus Iflavirus contain a single ORF with their structural proteins located at the 5'-end of the genome. HoVV-3, the third viral species was represented by only two ESTs from the dataset and formed a contig of 1,061 nt. The translated amino acid sequence was similar to the RdRp of Honey bee slow paralysis virus (SPV, 46%) and Kakugo virus (KV, 41%). Genome organization. Paralleling SBV, these ssRNA viral genomes contain 5'-proximal structural proteins and 3' nonstructural proteins. We report the initial discovery of three novel viruses infecting GWSS. Electron microscopic examinations confirmed isometric particles consistent with Picornavirales. A 2 year survey for HoCV-1 in GWSS throughout the USA revealed a widespread pattern of distribution. The virus was found to naturally infect adults and was not specific to life stage or gender. Discovery of new leafhopper pathogens provides new potential biological control agents for suppression of leafhopper pests.