Abstract
Many insects cultivate obligate endosymbionts for nutrition. Genomic analyses, coupled with physiological evidence demonstrate that insects and their obligate endosymbionts are intimately integrated in biosynthesis of essential nutrients, including essential amino acids. However, the mechanisms that underlie regulation of host/endosymbiont integrations remain elusive. Using sap-feeding insects, I investigated the role of amino acid transporters and microRNAs in host/endosymbiont integrations. In the first data chapter in aphids, I determined the localization of aphid glutamine transporter ApGLNT1 and another amino acid transporter ACYPI008971. ApGLNT1 specifically localizes at the plasma membrane of bacteriocytes, the aphid specialized cells harboring the endosymbiont Buchnera aphidicola. ACYPI008971 localizes at the symbiosomal membrane, a host derived membrane that surrounds each Buchnera cell. In the second data chapter, I determined the role of miRNAs in regulation of host/endosymbiont integration. I found fourteen conserved aphid microRNAs differentially expressed in the symbiotic tissue containing bacteriocytes versus a non- symbiont tissue gut. Those microRNAs potentially target genes involved in amino acid biosynthesis and signal transduction mechanisms. In the third data chapter, I functionally validated one of the predicted miRNA::mRNA interactions using a dual luciferase assay in NIH/3T3 cell culture. In the fourth data chapter, I expanded my investigation of miRNA functions from aphids to sap-feeding insects. I found the majority of microRNAs detected in the bacteriocyte cells of two species of aphids, a psyllid and a mealybug could potentially target their endosymbiont genomes. The distribution of Cluster of Orthologous Groups (COG) of the miRNA targets in the nutritional endosymbiont reflects the COG distribution of the symbiont genomes, indicating that these cross- kingdom miRNA::mRNA interactions are governed by random processes. Together, these studies contribute to elucidation of the mechanisms that underlie the regulation of host/endosymbiont integrations and shed light on the coevolution of hosts and their associated endosymbionts.