A single mutation weakens symbiont-induced reproductive manipulation through reductions in deubiquitylation efficiency

Abstract

Animals interact with microbes that affect their performance and fitness, including endosymbionts that reside inside their cells. Maternally transmittedWolbachiabacteria are the most common known endosymbionts, in large part because of their manipulation of host reproduction. For example, manyWolbachiacause cytoplasmic incompatibility (CI) that reduces host embryonic viability whenWolbachia-modified sperm fertilize uninfected eggs. Operons termedcifscontrol CI, and a single factor (cifA) rescues it, providingWolbachia-infected females a fitness advantage. Despite CI’s prevalence in nature, theory indicates that natural selection does not act to maintain CI, which varies widely in strength. Here, we investigate the genetic and functional basis of CI-strength variation observed among sisterWolbachiathat infectDrosophila melanogastersubgroup hosts. We cloned, Sanger sequenced, and expressedcifrepertoires from weak CI–causingwYak inDrosophila yakuba, revealing mutations suspected to weaken CI relative to modelwMel inD. melanogaster. A single valine-to-leucine mutation within the deubiquitylating (DUB) domain of thewYakcifBhomolog (cidB) ablates a CI-like phenotype in yeast. The same mutation reduces both DUB efficiency in vitro and transgenic CI strength in the fly, each by about twofold. Our results map hypomorphic transgenic CI to reduced DUB activity and indicate that deubiquitylation is central to CI induction incidsystems. We also characterize effects of other genetic variation distinguishingwMel-likecifs. Importantly, CI strength determinesWolbachiaprevalence in natural systems and directly influences the efficacy ofWolbachiabiocontrol strategies in transinfected mosquito systems. These approaches rely on strong CI to reduce human disease.