Simulating immunosuppressive mechanism of Microplitis bicoloratus bracovirus coordinately fights Spodoptera frugiperda.

Parasitoid wasps control pests via a precise attack leading to the death of the pest. However, parasitoid larvae exhibit self-protection strategies against bracovirus-induced reactive oxygen species impairment. This has a detrimental effect on pest control. Here, we report a strategy for simulating Microplitis bicoloratus bracovirus using Mix-T dsRNA targeting 14 genes associated with transcription, translation, cell-cell communication, and humoral signaling pathways in the host, and from wasp extracellular superoxide dismutases. We implemented either one-time feeding to the younger instar larvae or spraying once on the corn leaves, to effectively control the invading pest Spodoptera frugiperda. This highlights the conserved principle of "biological pest control," as elucidated by the triple interaction of parasitoid-bracovirus-host in a cooperation strategy of bracovirus against its pest host.

Bracovirus Sneaks Into Apoptotic Bodies Transmitting Immunosuppressive Signaling Driven by Integration-Mediated eIF5A Hypusination.

A typical characteristics of polydnavirus (PDV) infection is a persistent immunosuppression, governed by the viral integration and expression of virulence genes. Recently, activation of caspase-3 by Microplitis bicoloratus bracovirus (MbBV) to cleave Innexins, gap junction proteins, has been highlighted, further promoting apoptotic cell disassembly and apoptotic body (AB) formation. However, whether ABs play a role in immune suppression remains to be determined. Herein, we show that ABs transmitted immunosuppressive signaling, causing recipient cells to undergo apoptosis and dismigration. Furthermore, the insertion of viral-host integrated motif sites damaged the host genome, stimulating eIF5A nucleocytoplasmic transport and activating the eIF5A-hypusination translation pathway. This pathway specifically translates apoptosis-related host proteins, such as P53, CypA, CypD, and CypJ, to drive cellular apoptosis owing to broken dsDNA. Furthermore, translated viral proteins, such Vank86, 92, and 101, known to complex with transcription factor Dip3, positively regulated DHYS and DOHH transcription maintaining the activation of the eIF5A-hypusination. Mechanistically, MbBV-mediated extracellular vesicles contained inserted viral fragments that re-integrated into recipients, potentially via the homologous recombinant repair system. Meanwhile, this stimulation regulated activated caspase-3 levels via PI3K/AKT 308 and 473 dephosphorylation to promote apoptosis of granulocyte-like recipients Sf9 cell; maintaining PI3K/AKT 473 phosphorylation and 308 dephosphorylation inhibited caspase-3 activation leading to dismigration of plasmatocyte-like recipient High Five cells. Together, our results suggest that integration-mediated eIF5A hypusination drives extracellular vesicles for continuous immunosuppression.

Interactions of Vank proteins from Microplitis bicoloratus bracovirus with host Dip3 suppress eIF4E expression.

Microplitis bicoloratus bracovirus (MbBV) inhibits the immune response of the host Spodoptera litura by disrupting nuclear factor (NF)-κB signaling and downstream gene expression. However, the underlying molecular mechanisms are not well understood. Herein, we report that viral ankyrin (Vank) proteins interacted with host dorsal-interacting protein 3 (Dip3) to selectively inhibit the transcription of eukaryotic translation initiation factor 4 E (eIF4E). Dip3 and Vank proteins were co-expressed and colocalized in the nucleus. Furthermore, ectopic expression of Dip3 rescued the transcription of some NF-κB-dependent genes suppressed by Vank proteins, including eIF4E. Co-immunoprecipitation and pull-down assays confirmed that Vank proteins interacted with and bound to full-length Dip3, which including MADF, DNA-binding protein, BESS, and protein-protein interaction motifs as well as non-motif sequences. In vivo, RNAi-mediated dip3 silencing decreased eIF4E levels and was accompanied by an immunosuppressive phenotype in S. litura. Our results provided novel insights into the regulation of host transcription during immune suppression by viral proteins that modulate nuclear NF-κB signaling.