Innexin DNA-binding domains regulate Microplitis bicoloratus bracoviral transcription in symbiotic wasps

Bracoviruses have two hosts: symbiotic wasps and infected hosts. Although symbiotic wasps and infected Spodoptera litura larva host bracoviruses, mature virions form only in the wasps after the integrated Microplitis bicoloratus bracovirus (MbBV) proviral genome replicates. However, the associated mechanisms of transcription regulation have not been characterized. Here, we found that innexins (Inxs) of the Microplitis bicoloratus wasp (Mb-Inx1 and Mb-Inx2) contain DNA-binding domains that directly bind to, and regulate transcription promoters of the viral envelope genes MbBVp74 and MbBVe56-1. Transmission electron microscopy revealed that Mb-Inx1 and Mb-Inx2 RNA interference cause abnormal bracoviral virion formation. This led to inhibited virion assembly in wasp ovaries and downregulated envelope genes that are analogous to baculovirus proteins. The ectopic expression of Mb-Inx1 and Mb-Inx2 in the Bac-to-Bac Baculovirus expression system promoted nuclear polyhedra formation. We propose that unique bracoviral transcription strategies regulated by wasp Inx proteins govern virus-wasp interactions.