One prophage WO gene rescues cytoplasmic incompatibility in .

are maternally inherited, intracellular bacteria at the forefront of vector control efforts to curb arbovirus transmission. In international field trials, the cytoplasmic incompatibility (CI) drive system of Mel is deployed to replace target vector populations, whereby a -induced modification of the sperm genome kills embryos. However, in the embryo rescue the sperm genome impairment, and therefore CI results in a strong fitness advantage for infected females that transmit the bacteria to offspring. The two genes responsible for the Mel-induced sperm modification of CI, and , were recently identified in the eukaryotic association module of prophage WO, but the genetic basis of rescue is unresolved. Here we use transgenic and cytological approaches to demonstrate that maternal expression independently rescues CI and nullifies embryonic death caused by Mel in Discovery of as the rescue gene and previously one of two CI induction genes establishes a "Two-by-One" model that underpins the genetic basis of CI. Results highlight the central role of prophage WO in shaping phenotypes that are significant to arthropod evolution and vector control.