Type III CI factors from wAlbB induce cytoplasmic incompatibility via a Host Modification mechanism

The widespread prevalence of the endosymbiotic bacterium Wolbachia among insect species relies on its ability to invade and manipulate host reproduction via several ways, among which cytoplasmic incompatibility (CI) is most studied. Two non-mutually exclusive models, the Host-Modification (HM) and the Toxin-Antidote (TA), have been proposed to explain the molecular basis of CI. Here, we investigate the CI-inducing activity of the Type III CI factors (cifs) from wAlbB, a strain currently being deployed to combat mosquito-borne diseases. This set of Cifs displays conserved subcellular localization dynamics in various insect cells. Both cifA and cifB are required for the induction of DNA damage in cultured cells, and transgenic Drosophila. Moreover, these cifs induce CI in Drosophila through the two-by-one manner, meaning cifA and cifB act together during spermatogenesis to induce CI, and maternal cifA can reverse the effect. Mechanistically, genetic, biochemical, cellular, and proteomic analyses reveal that this pair of cifs acts during the early stage of spermatogenesis but is dispensable in late-stage germline cells for CI induction. Collectively, our findings support the notion that wAlbB Type III cifs induce CI via a HM-based mechanism. Additional analyses suggest that different Wolbachia strains may employ distinct molecular mechanisms to induce CI.