The mitochondrial genome of the brown citrus aphid Aphis (Toxoptera) citricidus: Insights into the repeat regions in aphids and phylogenetic implications.

We sequenced the complete mitochondrial (mt) genome of brown citrus aphid, Aphis (Toxoptera) citricidus (Kirkaldy) and compared it with that of other aphids. The mt genome of A. citricidus is a circular molecule of 16,763 bp with 84.0% AT content, containing 13 protein-coding genes (PCGs), 2 rRNAs, 22 tRNAs, a control region (CR) and an additional repeat region between trnE and trnF. Like other aphids, A. citricidus was slightly A-skewed (0.073) and strongly C-skewed (-0.309). Most PCGs used standard ATW start codons and TAA stop codons except nad4, which terminates with an incomplete codon T. All tRNAs and rRNA could be folded as typical secondary structures, except for lacking a dihydrouridine (DHU) arm in tRNASer (AGN). The repeat region possessed the most copy number of repeat motif (~7.5 times) among the reported aphid mt genomes, like in Acyrthosiphon pisum. Both Bayesian inference (BI) and Maximum likelihood (ML) analyses suggested that Toxoptera citricidus should revert to Aphis citricidus. The subfamily Aphidinae is monophyletic, but the Eriosomatinae is non-monophyletic. This study provides new insight into the evolution of aphid mt genomes, as well as useful information for resolving aphid phylogenetic questions.