Comparative analysis of amino acid transporters in aphids and mealybugs in the context of the maintenance of intracellular symbiosis

Phloem sap-feeding insects like aphids, whiteflies and mealybugs rely on intracellular bacteria to compensate their unbalanced diet, which is deficient in essential amino acids. Since the bacterial symbionts of these insects are bound by membranes within specialized insect cells called bacteriocytes, amino acid sharing between host and symbiont must be accomplished using membrane bound amino acid transporters. Recent evidence that gene duplications in amino acid transporters may facilitate the maintenance of symbiosis in aphids inspired us to investigate whether amino acid transporter duplications are also found in other phloem-feeding taxa, such as mealybugs. We used next-generation sequencing to reconstruct the whole insect and bacteriocyte trascriptome for the mealybug Planococcus citri. We then searched the two transcriptomes, using hidden markov models based on characteristic protein domains, for amino acid transporters. Here we describe the amino acid transporters we found in P. citri, their phylogenetic relationships among amino acid transporters in other insects, and compare expression profiles with aphid amino acid transporters in the context of symbiotic maintenance.