Portiera getswild: Genome instability provides insights into the evolution of bothwhiteflies and their endosymbionts

Whiteflies (Hemiptera: Sternorrhyncha: Aleyrodidae) are a superfamily of small phloem-feeding insects. They rely on their primary endosymbionts "Candidatus Portiera aleyrodidarum"to produce essential amino acids not present in their diet. Portiera has been codiverging with whiteflies since their origin and therefore reflects its host's evolutionary history. Like in most primary endosymbionts, the genome of Portiera stays stable across the Aleyrodidae superfamily after millions of years of codivergence. However, Portiera of thewhitefly Bemisia tabaci has lost the ancestral genome order, reflecting a rare event in the endosymbiont evolution: The appearance of genome instability. To gain a better understanding of Portiera genome evolution, identify the time point in which genome instability appeared and contribute to the reconstruction ofwhitefly phylogeny,we developed a newphylogenetic framework. It targeted five Portiera genes and determined the presence of the DNA polymerase proofreading subunit (dnaQ) gene, previously associated with genome instability, and two alternative gene rearrangements. Our results indicated that Portiera gene sequences provide a robust tool for studying intergenera phylogenetic relationships in whiteflies. Using these new framework, we found that whitefly species from the Singhiella, Aleurolobus, and Bemisia genera form a monophyletic tribe, the Aleurolobini, and that their Portiera exhibitgenomeinstability. This instability likely aroseonce in the commonancestorof the Aleurolobini tribe (at least 70Ma), drawing a link between the appearance of genome instability in Portiera and the switch from multibacteriocyte to a singlebacteriocyte mode of inheritance in this tribe.