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 transmitted <i>Wolbachia</i> bacteria are the most common known endosymbionts, in large part because of their manipulation of host reproduction. For example, many <i>Wolbachia</i> cause cytoplasmic incompatibility (CI) that reduces host embryonic viability when <i>Wolbachia</i>-modified sperm fertilize uninfected eggs. Operons termed <i>cifs</i> control CI, and a single factor (<i>cifA</i>) rescues it, providing <i>Wolbachia</i>-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 sister <i>Wolbachia</i> that infect <i>Drosophila melanogaster</i> subgroup hosts. We cloned, Sanger sequenced, and expressed <i>cif</i> repertoires from weak CI-causing <i>w</i>Yak in <i>Drosophila yakuba</i>, revealing mutations suspected to weaken CI relative to model <i>w</i>Mel in <i>D. melanogaster</i> A single valine-to-leucine mutation within the deubiquitylating (DUB) domain of the <i>w</i>Yak <i>cifB</i> homolog (<i>cidB</i>) 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 in <i>cid</i> systems. We also characterize effects of other genetic variation distinguishing <i>w</i>Mel-like <i>cifs</i> Importantly, CI strength determines <i>Wolbachia</i> prevalence in natural systems and directly influences the efficacy of <i>Wolbachia</i> biocontrol strategies in transinfected mosquito systems. These approaches rely on strong CI to reduce human disease.