Multiple Rescue Factors Within a Wolbachia Strain

Abstract

Wolbachia-induced cytoplasmic incompatibility (CI) is expressed when infected males are crossed with either uninfected females or females infected with Wolbachia of different CI specificity. In diploid insects, CI results in embryonic mortality, apparently due to the the loss of the paternal set of chromosomes, usually during the first mitotic division. The molecular basis of CI has not been determined yet; however, several lines of evidence suggest that Wolbachia exhibits two distinct sex-dependent functions: in males, Wolbachia somehow ''imprints'' the paternal chromosomes during spermatogenesis (mod function), whereas in females, the presence of the same Wolbachia strain(s) is able to restore embryonic viability (resc function). On the basis of the ability of Wolbachia to induce the modification and/or rescue functions in a given host, each bacterial strain can be classified as belonging in one of the four following categories:, and mod 1 resc À . A so-called ''suicide'' mod 1 resc À strain has not been found in nature yet. Here, a combination of embryonic cytoplasmic injections and introgression experiments was used to transfer nine evolutionary, distantly related Wolbachia strains (wYak, wTei, wSan, wRi, wMel, wHa, wAu, wNo, and wMa) into the same host background, that of Drosophila simulans (STCP strain), a highly permissive host for CI expression. We initially characterized the modification and rescue properties of the Wolbachia strains wYak, wTei, and wSan, naturally present in the yakuba complex, upon their transfer into D. simulans. Confocal microscopy and multilocus sequencing typing (MLST) analysis were also employed for the evaluation of the CI properties. We also tested the compatibility relationships of wYak, wTei, and wSan with all other Wolbachia infections. So far, the cytoplasmic incompatibility properties of different Wolbachia variants are explained assuming a single pair of modification and rescue factors specific to each variant. This study shows that a given Wolbachia variant can possess multiple rescue determinants corresponding to different CI systems. In addition, our results: (a) suggest that wTei appears to behave in D. simulans as a suicide mod 1 resc À strain, (b) unravel unique CI properties, and (c) provide a framework to understand the diversity and the evolution of new CI-compatibility types. WOLBACHIA is a group of maternally transmitted intracellular bacteria that infect numerous arthropod as well as filarial nematode species (Werren 1997;Bandi et al. 1998;Stouthamer et al. 1999). In arthropod hosts, Wolbachia mainly reside in ovaries and testes. In many cases, they manipulate host reproduction to ensure their own transmission by inducing feminization (Rigaud 1997), thelytokous parthenogenesis (Huigens and Stouthamer 2003), male killing (Hurst et al. 2003) and, most commonly, cytoplasmic incompatibility (CI) . In diploid species, CI is expressed as embryonic lethality of the progeny of a male infected by one (or more) Wolbachia strain(s) and a female that either is u...

Rapid evolution ofWolbachiaincompatibility types

“…Each new CI type observed here resulted from the gain of a new resc function with no apparent change in its mod function. This supports the notion that the mod and resc functions vary independently, in agreement with the fact that these functions are encoded by different genes of the Wolbachia genome [8,11,12,15,16].…”

Loss of reproductive parasitism following transfer of male-killing Wolbachia to Drosophila melanogaster and Drosophila simulans

“…Cytoplasmic donor was D. innubila infected with the wInn male-killing Wolbachia strain (Dyer and Jaenike, 2004). Recipient lines were uninfected lines iso31 for D. melanogaster and STCP for D. simulans that have nearly homozygous genetic backgrounds and have been used repeatedly in our laboratory for Wolbachia transfers (Zabalou et al, 2008).…”

“…Presence of Wolbachia in transinfected flies was checked every generation by STE/boiling method for DNA extraction and subsequent PCR using primers for 16S recombinant DNA or wsp genes (O'Neill et al, 1992;Zabalou et al, 2008). The Wolbachia strain(s) of the donor and of the transinfected Drosophila hosts were genotyped using a Multi Locus Sequence Typing system developed in Paraskevopoulos et al (2006).…”

“…D. innubila is naturally infected with a strain of Wolbachia (wInn) that experiences nearly perfect maternal transmission and causes B100% mortality of infected male embryos (Dyer and Jaenike, 2004). D. melanogaster and D. simulans both harbor natural Wolbachia infections that cause CI (Hoffmann et al, 1986;Hoffmann and Turelli, 1988;O'Neill and Karr, 1990;Bourtzis et al, 1996;Zabalou et al, 2008). The expression of CI is particularly strong in D. simulans.…”

Host genotype changes bidirectional to unidirectional cytoplasmic incompatibility in Nasonia longicornis

“…When CI occurs reciprocally between two different Wolbachia strains, they are referred to as bidirectionally incompatible. Apparent 'non-functional' and partially functional (for example, modification-deficient but rescue-competent) CI types are also known (Giordano et al, 1995;Hoffmann et al, 1996;Bourtzis et al, 1998;Charlat et al, 2003;Zabalou et al, 2008). Presence of more than one incompatibility type has been found in a number of different insects including mosquitoes, fruit flies, beetles and wasps (Laven, 1959;Breeuwer and Werren, 1990;O'Neill and Karr, 1990;Montchamp-Moreau et al, 1991;PerrotMinnot et al, 1996;Bordenstein et al, 2001).…”