Transovarial transmission of a core virome in the Chagas disease vector Rhodnius prolixus

Abstract

Triatomine assassin bugs comprise hematophagous insect vectors of Trypanosoma cruzi, the causative agent of Chagas disease. Although the microbiome of these species has been investigated to some extent, only one virus infecting Triatoma infestans has been identified to date. Here, we describe for the first time seven (+) single-strand RNA viruses (RpV1-7) infecting Rhodnius prolixus, a primary vector of Chagas disease in Central and South America. We show that the RpVs belong to the Iflaviridae, Permutotetraviridae and Solemoviridae and are vertically transmitted from the mothers to the progeny via transovarial transmission. Consistent with this, all the RpVs, except RpV2 that is related to the entomopathogenic Slow bee paralysis virus, established persistent infections in our R. prolixus colony. Furthermore, we show that R. prolixus ovaries express 22-nucleotide viral siRNAs (vsiRNAs), but not viral piRNAs, that originate from the processing of dsRNA intermediates during viral replication of the RpVs. Interestingly, the permutotetraviruses and sobemoviruses display shared pools of vsiRNAs that might provide the basis for a cross-immunity system. The vsiRNAs are maternally deposited in the eggs, where they likely contribute to reduce the viral load and protect the developing embryos. Our results unveil for the first time a complex core virome in R. prolixus and begin to shed light on the RNAi-based antiviral defenses in triatomines.

The Neglected Virome of Triatomine Insects

“…Recently, our group expanded the variety of viral species in triatomines by describing 7 unique viral genomes in Rhodnius prolixus (16). The RpVs are (+) single strand RNA viruses classified in three different families: Iflaviridae (RpV1 and RpV2), Permutotetraviridae (RpV3, RpV4 and RpV7) and Solemoviridae (RpV5 and RpV6) (16) and do not share any similarity with TrV (Figure 1A and Table 1).…”

“…RpV1 has the longest contig found (9.6 Kilobases) and it exhibits two main ORFs with amino acid sequence identity 36.99% and 40.88% with the proteins encoded by ORF1 and ORF2 of the Nesidiocoris tenuis virus 1 (NtV-1), respectively (16). NtV-1 has been classified in the Iflavirus genus, even though its genome revealed two different ORFs (62).…”

“…ORF1 of RpV1 encodes putative structural capsid proteins related to Cricket Paralysis virus (CrPV) and Picornavirales order specific proteins such as RhV-like (Figure 1B). ORF2 instead encodes putative non-structural proteins such as the RdRp enzyme and a RNA helicase (16). ORF1 and ORF2 of RpV1 display a 1-nt overlap typical of the Iflavirus genus, which results in a -1nt frame-shift (Figure 1B).…”

“…For instance, seminal studies by Sir V. B. Wigglesworth shed light on the hormonal control of oogenesis (10,11) as well as the role of the juvenile hormone in metamorphosis (11). In recent years, the sequencing and partial assembly of Rhodnius genome has spun novel genetic and genomic studies, which have started to unveil the molecular mechanisms underlying triatomine development, reproduction, immunity and evolution (6,(12)(13)(14)(15)(16)(17)(18). Substantial progress has also been achieved in the characterization of the triatomine microbiome, where a special focus was placed on symbiotic bacteria.…”

“…TrV was discovered in a colony of field-collected Triatoma infestans (38,40). Only recently, our group identified and characterized 7 novel viruses, namely Rhodnius prolixus virus 1-7 (RpV1-7), while investigating stage-specific de novo transcriptome assemblies in ovarian tissues of Rhodnius prolixus (16,17). This review aims to describe the (limited) information available on triatomine viruses and underscore the importance of investing in this neglected area of scientific research.…”