Wolbachia endosymbionts manipulate GSC self-renewal and differentiation to enhance host fertility

The alphaproteobacterium Wolbachia pipientis infects thousands of arthropod and nematode species worldwide, making it a key target for host biological control. Wolbachia-driven host reproductive manipulations, such as cytoplasmic incompatibility (CI), are often credited for catapulting these intracellular bacteria to high frequencies in their host populations. Positive, perhaps mutualistic, reproductive manipulations may also increase infection frequencies, but they are not well understood on molecular, cellular, or organismal levels. Previous studies demonstrated that Wolbachia is capable of partially rescuing sex-lethal, a gene required for germline stem cell (GSC) self renewal and bag-of-marbles, a gene required for GSC differentiation. Here, we identify molecular and cellular mechanisms by which Wolbachia is able to influence molecularly distinct processes of GSC self renewal and differentiation through our discovery that the wMel strain rescues meiotic-P26 mutants. Mei-P26 is an essential translational regulator and is required for both GSC self-renewal and differentiation. We demonstrate that wMel rescues the fertility of flies lacking adequate mei-P26 dosage and function, and is sufficient to sustain infertile homozygous mei-P26 hypomorphic stocks indefinitely. Cytology revealed that wMel infection mitigates the impact of mei-P26 loss on both germline stem cell maintenance and cyst differentiation through restoring proper pMad, Bam, Sxl, and Orb expression. Rescue in males, amplification of dominant negative effects, and multiallelic rescue suggest that wMel either directly or indirectly replaces Mei-P26 function. Even in wild-type individuals, wMel infection elevates lifetime egg lay and hatch rates. Over time, the beneficial fertility reinforcement mechanisms described here may promote the emergence of mutualism and the breakdown of CI. Graphical Abstract Highlights The wMel strain of Wolbachia restores fertility in females and males deficient for the essential translational regulator meiotic-P26 Mei-P26’s germline maintenance and oocyte cyst differentiation functions are genetically rescued by wMel infection Perturbed pMad, Sxl, Bam, and Orb expression are mitigated by wMel infection wMel infection elevates lifetime egg lay and hatch rates in wild-type flies