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