Submitted to: Journal of Insect Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/24/2006
Publication Date: 10/2/2006
Citation: Hunter, W.B., Katsar, C.S., Chaparro, J.X. 2006. Molecular analysis of capsid protein of Homalodisca coagulata Virus-1, a new leafhopper-infecting virus from the glassy-winged sharpshooter, Homalodisca coagulata. Journal of Insect Science. 6:28. Available: insect science.org/6.28/. Interpretive Summary: A new insect-infecting virus was isolated from the glassy-winged sharpshooter (GWSS) and is named, Homalodisca Coagulata Virus-1 (HoCV-1). The GWSS is an important vector of the plant pathogenic bacterium, known as Xylella, causes the plant disease Pierce's Disease of grapes. Introduced insects are attacked by native parasitoids, predators and pathogens the latter of which may be fungi, bacteria, or viruses. We noticed high mortality of 5th instar nymphs during attempts to rear GWSS. To determine if a pathogen was killing GWSS we chose a genetic approach. The genes we identified strongly supported the presence of an insect-infecting virus. The identity of the virus was made using the capsid proteins which have been shown to be a suitable target for these types of studies on other insect viruses. HoCV-1 had significant relatedness to members within the Family: Dicistroviridae, and appears to form a new clade within the newly recognized Genus: Cripavirus, "Cricket-Paralysis-like viruses". Structural analysis of the HoCV-1 capsid protein indicated the presence of four domains with significant structural homology with previously established Cripavirus crystalline structures. HoCV-1 was found to increase sharpshooter mortality and was infective through microinjection, spraying, and bathing of insects with crude viral preparations. HoCV-1 may have a use as a microbial biological control agent for managing the GWSS.
Technical Abstract: Invading insects are constantly exposed to new pathogens as they move into new environmental niches. Within these interactions of host and pathogen is the struggle of the pathogen to adapt to the newly introduced insect as a potential new host resource. In this case, we discovered a leafhopper-infecting virus, HoCV-1, that infects the Glassy-winged sharpshooter, GWSS (Hemiptera: Cicadellidae: Homalodisca coagulata). The HoCV-1 capsid protein has a molecular weight of approximately 97.94 kD and a pI of 5.69. The comparison of the predicted amino acid sequence of putative HoCV-1 capsid protein identified several clusters of conserved amino acids separated by large regions of low or no homology and gaps. Amino acid similarity between CP1-4 of CrPV and HoCV-1 ranged from less than 20% for CP1 and CP4 to 35% for CP2. The phylogenetic analysis performed using the optimized protein alignment generated a phylogram containing 5 clades. Clade 1: Drosophila C virus, Clade 2: Cricket paralysis virus, Clade 3: Triatoma virus, Plautia stali intestine virus, Himetobi P virus, Black Queen Cell virus, and HoCV-1. Clade 4: Acute bee paralysis virus and Kashmir Bee virus, and Clade 5: Rhopalosiphum padi virus. When the four capsid polyprotein units were analyzed individually HoCV-1 always fell within clade 3. The amino acid sequence alignment was scanned for putative cleavage sites of the capsid polyprotein. Viruses of this group typically have three cleavage sites. The order of the polyprotein subunits is CP2, CP4, CP3, CP1. The CP4/CP3 (AFGL/GKPK) cleavage boundary site was clearly aligned with all the aligned viruses. The putative CP3/CP1 (ADVQ/SAFA) site and the putative CP2/CP4 (VTMQ/EQSA) cleavage site of HoCV-1, respectively, were located in the same region as that of the other viruses. After alignment, the CP3/CP1 cleavage sites and CP2/CP4 cleavage sites of all viruses analyzed fell within 50 amino acids of one another. CP4 of HoCV-1 appeared to be mainly ?-helical in structure. CP1-4 Domains were most homologous to insect picorna-like virus coat proteins as demonstrated in the BLASTP and PSI-BLAST results, as well as in the structural modeling. Further research will need to focus on whether HoCV-1 can be used to reduce GWSS populations as a biological control agent.