Evolutionary Genetics of Cytoplasmic Incompatibility Genes cifA and cifB in Prophage WO of Wolbachia

Abstract

The bacterial endosymbiont Wolbachia manipulates arthropod reproduction to facilitate its maternal spread through host populations. The most common manipulation is cytoplasmic incompatibility (CI): Wolbachia-infected males produce modified sperm that cause embryonic mortality, unless rescued by embryos harboring the same Wolbachia. The genes underlying CI, cifA and cifB, were recently identified in the eukaryotic association module of Wolbachia’s prophage WO. Here, we use transcriptomic and genomic approaches to address three important evolutionary facets of the cif genes. First, we assess whether or not cifA and cifB comprise a classic toxin–antitoxin operon in wMel and show that the two genes exhibit striking, transcriptional differences across host development. They can produce a bicistronic message despite a predicted hairpin termination element in their intergenic region. Second, cifA and cifB strongly coevolve across the diversity of phage WO. Third, we provide new domain and functional predictions across homologs within Wolbachia, and show that amino acid sequences vary substantially across the genus. Finally, we investigate conservation of cifA and cifB and find frequent degradation and loss of the genes in strains that no longer induce CI. Taken together, we demonstrate that cifA and cifB exhibit complex transcriptional regulation in wMel, provide functional annotations that broaden the potential mechanisms of CI induction, and report recurrent erosion of cifA and cifB in non-CI strains, thus expanding our understanding of the most widespread form of reproductive parasitism.

Loss of cytoplasmic incompatibility and minimal fecundity effects explain relatively lowWolbachiafrequencies inDrosophila mauritiana

“…In contrast, our phylogram and that of Lindsey et al. () support w AlbB splitting from all other strains at this node. Second, the Gerth and Bleidorn () calibration estimated the split between w Ri that infects D. simulans and w Suz that infects D. suzukii at 900,000 years.…”

“…). The relationships we infer agree with those from recently published phylograms (Gerth and Bleidorn ; Lindsey et al ) (Fig. A).…”

“…; Lindsey et al. ). w No_RS01055 and w No_RS01050 are highly diverged from cidA‐cidB w Mel and cidA‐cidB w Pip homologs and from cinA‐cinB w Pip ; however, this w No pair is more similar to cinA‐cinB w Pip in terms of protein domains, lacking a ubiquitin‐like protease domain (Lindsey et al ).…”

Mi Casa es Su Casa: how an intracellular symbiont manipulates host biology

“…Indeed, expression of cifA or cifB alone increase CI and neither locus alone could rescue the CI‐induced defects. With regards to function, the w Mel and w Pip homologues of cifB encode functional deubiquitinase domains (Beckmann et al ., ), although the deubiquitinase (DUB) domain is not universally conserved among cifB homologues across the Wolbachia phylogeny (Lindsey et al ., ). In Drosophila melanogaster , the DUB domain in the w Pip cifB homologue ( cidB ) is critical for the induction of cytoplasmic incompatibility; transgenic flies expressing a construct lacking the catalytic residue do not exhibit a phenotype (Beckmann et al ., ).…”

“…The two Cif proteins seem to work synergistically, binding to each other in vitro (Beckmann et al ., ), and increases CI when expressed together in D. melanogaster (LePage et al ., ). Although the cif loci are syntenic and this genomic organization is conserved broadly across the Wolbachia phylogeny, there is little evidence of co‐transcription in w Mel (Lindsey et al ., ). Future mechanistic detail about Wolbachia cytoplasmic incompatibility will be revealed by answering the following questions: How do these proteins induce CI?…”