Most plants and animals are associated with microbial partners that shape their hosts' ability to use environmental resources and to persist under different conditions of stress and disease. These associated benefits select for hosts to maintain these symbiotic partners over generations. While accepting and maintaining beneficial microbes, hosts must also try to attenuate the effects of pathogenic ones. To better understand how animals accomplish this goal, this research characterizes the responses of the pea aphid, Acyrthosiphon pisum, to acquisition of beneficial and harmful bacteria. These insects are ideal candidates for this research because they have a well-studied association with symbiotic bacteria but are also hampered by bacterial pathogens. In this project, variation in susceptibility to pathogens and acceptance of symbionts will be assessed by experimentally measuring these traits in different aphid lineages. Immunological assays will be used to investigate cell-based immune responses, and sequencing technology will be employed to investigate expression of immune response genes. Results will significantly advance our understanding of host susceptibility, immunity and stress in relation to beneficial and harmful microbial associates. Generation of large amounts of genetic data, which will be deposited online at AphidBase and GenBank, will facilitate ongoing annotation of the pea aphid genome, thus providing resources for future studies of a significant agricultural pest. This project will fund training of one graduate student, one postdoctoral researcher, a middle school teacher, and several minority undergraduates. Additionally, results of the research project will be used as the basis for a novel art and science collaboration, in which scientists will work with student artists and minority-serving after school programs to explore how artistic interpretations of scientific results can be used to make research publicly accessible.
Many organisms are host to beneficial microbes that help them process food and protect them from pathogens and environmental stressors. While maintaining these advantageous associations, plants and animals must still defend themselves from harmful microbial pathogens. We used the association between aphids (small garden insect pests) and beneficial bacteria to explore how a host differentially responds to the presence of beneficial and harmful pathogens. We identified several types of aphid immune cells and the ability of these cells to target pathogens and symbiotic bacteria. We found that aphids with beneficial bacteria have more of these immune cells than aphids without beneficial bacteria during certain life stages, suggesting that these cells may play a role in regulating beneficial bacterial populations. We also determined how immune cell numbers and numbers of beneficial bacteria change upon pathogen infection. Overall, responses to fungal pathogens appear stronger than responses to bacterial pathogens. Finally, we assessed host responses towards the introduction of pathogens and beneficial bacteria through high throughput sequence analyses that capture what genes aphids use during these interactions. In this respects, aphids, compared to many other insects, appear to respond very weakly towards the introduction of bacteria, be they friend or foe. However, we have identified several genes not previously known to be associated with insect immunity that are utilized by aphids upon introduction of bacteria, providing new insights into both aphids and into invertebrate immune responses. Aphids and their association with beneficial bacteria provide a excellent model for the public to gain appreciation for the importance of beneficial microbes for the health of plants and animals, including themselves. During the course of the grant, we developed two teaching modules implemented in an Atlanta area high school biology course and we used aphids in one afterschool middle school program and one science and technology symposium targeting middle school girls. At the undergraduate level, discussion of aphids and their beneficial bacteria were integrated into a larger interdisciplinary art and science course, where students made ceramics pieces based on science themes, and we have provided aphids for a project in an undergraduate biology course and Auburn University. Twelve undergraduate students participated in research directly related to this project, and many of these students have gone on to graduate and medical school. Two graduate students and three post docs were trained as part of this project as well.
