Evaluating the essentiality of the primary endosymbiont of the rice weevil Sitophilus oryzae through genome analysis

International audience; The rice weevil Sitophilus oryzae is a pest insect responsible for great economic losses to the agriculture, particularly in developing countries where the damage can exceed 40% of the cereal production. This pest harbors an endosymbiont, “Candidatus Sodalis pierantonius” (cited Sodalis hereafter) that improves its fitness and invasive power. It has been demonstrated that Sodalis recently replaced the ancestral endosymbiont “Candidatus Nardonella” (cited Nardonella hereafter), which is still conserved in other members of the Dryophthoridae family. This recent acquisition raises several challenges for the host, given that the genome of Sodalis has not experienced a drastic genome size shrinkage when compared to other old-lasting insect’s endosymbionts. While the genomes of Sodalis and several strains of Nardonella are available, the insect’s genome is still needed to perform a full study of the system. To this end, we have sequenced and assembled the full genome of the weevil S. oryzae using a combination of Next Generation Sequencing data. Additionally, we have compared this genome with other available insect genomes. We found that the genome of S. oryzae encodes immune elements similar to those of other holometabolous insects, including those living without endosymbionts. Remarkably, an impressive amount of repeated elements was identified, similar to what was previously described in the Sodalis endosymbiont, suggesting the occurrence of gene rearrangement processes at this early phase of symbiogenesis. We concluded that while Sodalis is completely dependent on its host, the insect can survive without its endosymbiont.