Title: Genomic and proteomic analysis of Schizaphis graminum reveals cyclophilin proteins are involved in the transmission of Cereal yellow dwarf virus Authors
|Tamborindeguy, Cecilia -|
|Bereman, Michael -|
|Igwe, David -|
|Smith, Dawn -|
|White, Frank -|
|Maccoss, Michael -|
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2013
Publication Date: N/A
Interpretive Summary: The RPV strain of Cereal yellow dwarf virus is transmitted by aphids and is part of a larger family of viruses that infect potato, wheat, oats, barley, and rye. These viruses cause serious economic problems for farmers in the United States and worldwide. Virus transport through the aphid vector requires carefully tuned protein interactions at different tissue barriers in the insect, for example at the gut or salivary tissues. The greenbug aphid, Schizaphis graminum, is a useful aphid species to understand how proteins regulate transmission because there are many lab and field-collected populations that vary in their ability to transmit virus, i.e., some populations are good vectors that transmit virus efficiently and other populations are non-vectors that do not transmit virus. Previous work in the lab focused on comparing proteins from vectors and non-vectors to discover the ones that could be important to virus transmission. Our previous work showed that two forms of a protein called cyclophilin were detected in a handful of lab-reared greenbug populations, and one of these forms was always found in vector populations. Here, we show that one form of cyclophilin is a biomarker for vector populations of the greenbug distributed throughout the United States that efficiently transmit RPV. We show that the two forms of cyclophilin protein are produced in the aphid populations because there is a single difference in the cyclophilin gene in these greenbug populations. This difference enables the greenbugs to produce the two different protein forms. Our experiments also reveal that cyclophilin proteins can interact directly with RPV and lead us to hypothesize that cyclophilin proteins assist the RPV virus in moving across the insect gut. Our study indicates that although cyclophilin proteins are important to the virus transmission process, there are other proteins that play an important role in virus transmission that remain to be discovered. The work presents the most information on any protein involved in transmission of Cereal yellow dwarf virus, to date. This new information may enable us to develop novel strategies that block RPV transmission by aphids.
Technical Abstract: Yellow dwarf viruses cause the most economically important virus diseases of cereal crops worldwide and are transmitted by aphid vectors. The identification of aphid genes and proteins mediating virus transmission is critical to develop agriculturally sustainable virus management practices and to understand viral strategies for circulative movement in all insect vectors. Two cyclophilin B proteins, S28 and S29, were identified previously in populations of Schizaphis graminum that differed in their ability to transmit the RPV strain of Cereal yellow dwarf virus (CYDV-RPV). The presence of S29 was correlated with F2 genotypes that were efficient virus transmitters. The present study revealed the two proteins were isoforms, and a single amino acid change distinguished S28 and S29. The distribution of the two alleles was determined in 12 F2 genotypes segregating for CYDV-RPV transmission capacity and in 11 genetically independent, field-collected S. graminum biotypes. Transmission efficiency for CYDV-RPV was determined in all genotypes and biotypes. The S29 isoform was present in all genotypes or biotypes that efficiently transmit CYDV-RPV and more specifically in genotypes that efficiently transport virus across the hindgut. We confirmed a direct interaction between CYDV-RPV and both S28 and S29 using purified virus and bacterially expressed, his-tagged S28 and S29 proteins. Importantly, S29 failed to interact with a closely related virus that is transported across the aphid midgut. We further tested for interactions using an aphid-virus co-immunoprecipitation strategy coupled with a bottom-up LC-MS/MS analysis using a Q Exactive mass spectrometer. This analysis enabled us to identify a third cyclophilin protein, cyclophilin A, interacting directly or in complex with purified CYDV-RPV. Taken together, this data provides evidence that both cyclophilin A and B interact with CYDV-RPV, and these interactions may be important but not sufficient to mediate virus transport from the hindgut lumen into the hemocoel.