"Aphids are insect pests that feed on plant phloem sap and cause feeding damages and transmission of plant pathogens. The pea aphid (Acyrthosiphon pisum) complex is consisted of multiple biotypes each of which specialized to specific legume plants. Aphids use a specialized mouth part to puncture plant phloem sieve cells and suck plant nutrients. During the feeding process, aphids secrete saliva which contains various proteins that might interact with plant proteins. Interestingly, the pea aphids carries various facultative symbionts and one of which, Regiella, is known to increase aphid adaptation to clover plants. This project aims to examine the role of aphid saliva proteins and aphid symbionts in host plant adaptation. Based on previous works in plant microbe interactions, I hypothesize that aphid saliva proteins function like microbial pathogen effectors. Thus, I anticipate that the saliva proteins that are involved in host adaptation process are under high evolutionary pressure and show differential expressions or polymorphisms between biotypes. I will examine transcription profiles and sequences of salivary gland genes of the aphids that belong to different biotypes. Aphid gene silencing and in planta transient protein expression will be employed to examine the roles of the saliva genes in plant-aphid interactions. I will also examine the Regiella strains that does/does not increase aphid adaptation to clover plant to understand the host adaptation mechanisms of the aphids. I will conduct transcription analysis and saliva proteomics of the pea aphids with and without the Regiella strains. The project will improve our knowledge on the roles of aphid saliva proteins and symbionts in plant-aphid specialization process and will be the first step to contribute to develop benign strategies to control aphids in the field."