Wolbachia elevates host methyltransferase expression to block an RNA virus early during infection

Abstract

Wolbachia pipientis is an intracellular endosymbiont known to confer host resistance against RNA viruses in insects. However, the causal mechanism underlying this antiviral defense remains poorly understood. To this end, we have established a robust arthropod model system to study the tripartite interaction involving Sindbis virus and Wolbachia strain wMel within its native host, Drosophila melanogaster. By leveraging the power of Drosophila genetics and a parallel, highly tractable D. melanogaster derived JW18 cell culture system, we determined that in addition to reducing infectious virus production, Wolbachia negatively influences Sindbis virus particle infectivity. This is further accompanied by reductions in viral transcript and protein levels. Interestingly, unchanged ratio of proteins to viral RNA copies suggest that Wolbachia likely does not influence the translational efficiency of viral transcripts. Additionally, expression analyses of candidate host genes revealed D. melanogaster methyltransferase gene Mt2 as an induced host factor in the presence of Wolbachia. Further characterization of viral resistance in Wolbachia–infected flies lacking functional Mt2 revealed partial recovery of virus titer relative to wild-type, accompanied by complete restoration of viral RNA and protein levels, suggesting that Mt2 acts at the stage of viral genome replication. Finally, knockdown of Mt2 in Wolbachia uninfected JW18 cells resulted in increased virus infectivity, thus demonstrating its previously unknown role as an antiviral factor against Sindbis virus. In conclusion, our findings provide evidence supporting the role of Wolbachia–modulated host factors towards RNA virus resistance in arthropods, alongside establishing Mt2’s novel antiviral function against Sindbis virus in D. melanogaster.

Wolbachia strain wAlbB blocks replication of flaviviruses and alphaviruses in mosquito cell culture

“…Interestingly, the same pattern was not observed for DENV or WNV KUN . These data suggest that, for some viruses, the block hypothesized to occur early in infection, possibly at the virus translation stage [57][58][59], may be delayed if the initial virus population is large. A possible explanation is that a large starting population size allows the virus to partially overcome the initial challenge imposed by Wolbachia in these cells.…”

“…A possible explanation is that a large starting population size allows the virus to partially overcome the initial challenge imposed by Wolbachia in these cells. However, subsequent cycles of infection may be hampered by low numbers of progeny viruses and the ability of Wolbachia to reduce the infectivity of these progeny [58,60], ultimately causing extinction of the virus.…”

Whole genome screen reveals a novel relationship between Wolbachia levels and Drosophila host translation

“…Wolbachia-mediated suppression of viral replication in hosts is well described [7,8,11,12,64]. Multiple mechanisms may underlie this observation including interference with viral entry and very early stages of viral replication [38,53,57,[64][65][66][67][68][69][70][71]. All viruses depend on host translation machinery for replication of their genomes.…”

Mi Casa es Su Casa: how an intracellular symbiont manipulates host biology

“…However, it has been shown that these loci are not necessary for Wolbachia to inhibit Dengue virus in D. melanogaster (Rances et al, 2012;. Recently, Wolbachia mediated transcriptional changes at another locus was implicated in pathogen blocking; Wolbachia infection significantly upregulates the Drosophila melanogaster cytosinemethyltransferase gene Mt2, and reduction or ablation of Mt2 function (either by knockdown or knockout) diminishes Wolbachia's ability to inhibit virus replication (Bhattacharya et al, 2017). The mechanism by which Wolbachia achieves this upregulation, however, is not yet known.…”