Vertical Transmission of Biosynthetic Plasmids in Aphid Endosymbionts ( Buchnera )

Abstract
This study tested for horizontal transfer of plasmids among Buchnera aphidicola strains associated with ecologically and phylogenetically related aphid hosts ( Uroleucon species). Phylogenetic congruence of Buchnera plasmid ( trpEG and leuABC ) and chromosomal ( dnaN and trpB ) genes supports strictly vertical long-term transmission of plasmids, which persist due to their contributions to host nutrition rather than capacity for infectious transfer. Synonymous divergences indicate elevated mutation on plasmids relative to chromosomal genes.