Background: Coevolution between modern aphids and their primary obligate, bacterial endosymbiont,Buchnera aphidicola, has been previously reported at different classification levels based on molecular phylogenetic analyses. However, theBuchneragenome remains poorly understood within theRhusgall aphids.Results: We assembled the complete genome of the endosymbiontBuchnerain 16 aphid samples, representing 13 species in all six genera ofRhusgall aphids by shotgun genome skimming method. We compared the newly assembled genomes with those from GenBank to comprehensively investigate patterns of coevolution between the bacteriaBuchneraand their aphid hosts.Buchneragenomes were mostly collinear, and the pan-genome contained 684 genes, in which the core genome contained 256 genes with some lineages having large numbers of tandem gene duplications. There has been substantial gene-loss in eachBuchneralineage. We also reconstructed the phylogeny forBuchneraand their host aphids, respectively, using 72 complete genomes ofBuchnera, along with the complete mitochondrial genomes and three nuclear genes of 31 corresponding host aphid accessions. The cophylogenetic test demonstrated significant coevolution between these two partner groups at individual, species, generic, and tribal levels.Conclusions: Buchneraexhibits very high levels of genomic sequence divergence but relative stability in gene order. The relationship between the symbiontsBuchneraand its aphid hosts shows a significant coevolutionary pattern and supports complexity of the obligate symbiotic relationship.

We sequenced the complete mitochondrial genome (mitogenome) for the North American Rhus gall aphid species Melaphis rhois. The mitogenome is 15,436 bp in length with a high A + T content of 82.7%, consisting of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region. Its gene order is identical to that of the eastern Asian species Schlechtendalia chinensis. All protein-coding genes start with a typical ATN codon and terminate with a TAA codon except COI and ND4 by a single T residue. All the tRNAs except tRNA^Cys formed a clover-leaf secondary structure. The mitogenome phylogeny of Aphididae suggests that M. rhois is most closely related to the eastern Asian Rhus gall aphid S. chinensis with the present sampling scheme.

We sequenced the complete mitochondrial genome of Hamamelistes spinosus using the shotgun genome-skimming method. The mitogenome of H. spinosus is 15,089 bp in length with a much higher A + T content of 81.8% than that of G + C (18.2%) and consists of 13 protein-coding genes (PCGs), 2 rRNA genes, 22 tRNA genes and 1 control region. All the 13 PCGs initiate with a typical ATN and end with TAA except for two genes COX1 and ND4, which terminate with a single T. All the tRNAs form a classical clover-leaf secondary structure except for tRNA-Ser (AGN), which does not have the dihydrouridine (DHU) arm. In addition, we constructed the phylogenetic tree of Aphididae with two species Adelges laricis and Daktulosphaira vitifoliae as outgroups and the results showed that Hamamelistes spinosus is sister to Hormaphis betulae and they are closely allied with Neothoracaphis yanonis.

We sequenced the first complete mitochondrial genome for the aphid subfamily, Eriosomatinae, from a Rhus gall aphid, Schlechtendalia chinensis. The mitogenome of S. chinensis is 16,047 bp in length with a high A + T content of 84.2% and consists of 13 protein-coding genes, 24 tRNA genes including two extra tRNA^Phe, two rRNA genes, a repeat region, and a control region. All protein-coding genes have a typical ATN initiation codon and TAA termination codon except COI and ND4, which terminate with a single T. All 24 tRNAs have the expected clover-leaf secondary structure and range in size from 62 to 73 bp. The lengths of rrnL and rrnS genes are 1274 and 772 bp, respectively. The repeat region is 335 bp and is uncommon among known aphid sequences for starting with a tRNA^Phe. The control region is 705 bp in length and is located between rrnS and tRNA^Ile. We present a phylogeny of mitogenomes showing that S. chinensis is sister to Aphidinae.