Detection of the Wolbachia protein WPIP0282 in mosquito spermathecae: Implications for cytoplasmic incompatibility

• Peptides encoded by wPip_0282 occur in sperm from dissected mosquito spermathecae.
• Homologs of wPip_0282 are only present in CI-inducing Wolbachia strains.
• wPip_0282 and wPip_0283 comprise a two gene operon that has duplicated and diverged.
• wPip_0283 encodes a C-terminal, eukaryotic SUMO protease domain.

Cytoplasmic incompatibility (CI) is a conditional sterility induced by the bacterium Wolbachia pipientis that infects reproductive tissues in many arthropods. Although CI provides a potential tool to control insect vectors of arthropod-borne diseases, the molecular basis for CI induction is unknown. We hypothesized that a Wolbachia-encoded, CI-inducing factor would be enriched in sperm recovered from spermathecae of female mosquitoes. Using SDS-PAGE and mass spectrometry, we detected peptides from the 56 kDa hypothetical protein, encoded by wPip_0282, associated with sperm transferred to females by Wolbachia infected males. We also detected peptides from the same protein in Wolbachia infected ovaries. Homologs of wPip_0282 and the co-transcribed downstream gene, wPip_0283, occur as multiple divergent copies in genomes of CI-inducing strains of Wolbachia. The operon is located in a genomic context that includes mobile genetic elements. The absence of wPip_0282 and wPip_0283 homologs from genomes of Wolbachia in filarial nematodes, as well as other members of the Rickettsiales, suggests a role as a candidate CI effector.

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