COMPLETE GENOME SEQUENCE AND MOLECULAR CHARACTERIZATION OF HOMALODISCA COAGULATA VIRUS-1, A NOVEL VIRUS DISCOVERED IN THE GLASSY-WINGED SHARPSHOOTER (HEMIPTERA: CICADELLIDAE)

Authors: Hunnicutt, Laura; Hunter, Wayne; CAVE, R - UNIV. OF FLORIDA; POWELL, C - UNIV. OF FLORIDA; Mozoruk, Jerry

Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2006
Publication Date: 5/8/2006
Citation: Hunnicutt, L.E., Hunter, W.B., Cave, R.D., Powell, C.A., Mozoruk, J.J. 2006. Genome sequence and molecular characterization of Homalodisca coagulata virus-1, a novel virus discovered in the glassy-winged sharpshooter (Hemiptera: Cicadellidae). Virology 350:67-78.

Interpretive Summary: The discovery of a new viral pathogen from the glassy-winged sharpshooter, GWSS, Homalodisca coagulata (Say), known as Homalodisca coagulata virus-1, HoCV-1 has been shown to increase mortality of GWSS populations. The GWSS is an important agricultural pest due to its’ ability to spread plant diseases of economic importance. Some examples are Pierce’s Disease of grapes, which is caused by a bacterial plant pathogen, Xylella fastidiosa. These bacterial caused diseases are commonly referred to as ‘Scorch’ diseases, due to the dry leaf appearance in infected, susceptible plants. In grapes, almonds, and other fruit tree crops, susceptible plants have reduced yields and may die after infection thus causing a long-term loss of profits to growers. To better understand how HoCV-1 may be used against the GWSS the full genome of the virus was sequenced. Genetic analyses showed that the virus belongs to a family of insect infecting viruses called, Dicistroviridae. These viruses are rapidly being discovered in many insect pests and are being examined for uses to reduce leafhopper populations in an environmentally friendly fashion. Natural infections of HoCV-1 in field populations of GWSS are estimated to reduce GWSS by 20-30 % and may already be aiding current efforts to suppress the spread of Pierce’s Disease and other “Scorch” like diseases. Examination of the HoCV-1 genes will aid our understanding of how this virus infects and replicates inside GWSS. Our understanding of the virus/leafhopper interactions will help us further by knowing how best to use this new viral pathogen to protect agricultural crops.

Technical Abstract: Few viral pathogens of leafhoppers have been discovered or examined as potential microbial control agents. The recent discovery of HoCV-1 a virus which infects and kills glassy-winged leafhoppers, GWSS, Homalodisca coagulata, (Hemiptera: Cicadellidae) provides a unique opportunity to better understand viral/leafhopper interactions. GWSS is an important vector of Xylella caused diseases. The best known example is Pierce’s Disease of grapes. However, the bacterial complex of Xylella fastidiosa, also causes many different diseases which affect fruit trees and woody crops. The complete nucleotide sequence of this novel single-stranded RNA virus, Homalodisca coagulata virus-1 (HoCV-1) has been determined. In silico analysis of HoCV-1 revealed a 9321 nt polyadenylated genome encoding two large open reading frames (ORF1 and ORF2) separated by a 179 nt intergenic region (IGR). The deduced amino acid sequence of the 5'-proximal ORF (ORF1, nt 420-5807) exhibited conserved core motifs characteristic of the helicases, cysteine proteases, and RNA-dependent RNA polymerases of other insect-infecting picorna-like viruses. A structural model created using M-FOLD exposed a series of stem-loop (SL) structures immediately preceding the second ORF which are analogous to an internal ribosome entry site (IRES), suggesting that ORF2 begins with a noncognate GCA triplet rather than the canonical AUG. This 3' ORF2 (nt 5987-8740) showed significant similarity to the structural proteins of members of the family Dicistroviridae, particularly those belonging to the genus Cripavirus. Evidence demonstrating relatedness of these viruses regarding genome organization, amino acid sequence similarity, and putative replication strategy substantiate inclusion of HoCV-1 into this taxonomic position. HoCV-1 as the first virus reported from GWSS is being evaluated for potential use as a microbial biological control agent to augment current management strategies against the GWSS.