UC Riverside

Microbial symbionts in animals affect various processes and can be mutualistic, commensal, or parasitic. Symbionts can be obligate or facultative, depending on their requirement for host survival. Insects, particularly herbivores, often form intimate associations with symbiotic microbes involved in nutrient synthesis and plant material digestion. Psyllids, a group of sap-feeding insects, are known to associate with obligate symbiont "Candidatus Carsonella ruddii," which synthesizes essential amino acids for the psyllid's nitrogen-poor diet. Psyllids also harbor facultative symbionts from diverse lineages, horizontally transmitted and prevalent in many species. In psyllids, some facultative symbionts act as both plant pathogens and endosymbionts, such as Candidatus Liberibacter species, which circulate throughout the psyllid's body and may benefit the psyllid by suppressing plant defenses. Despite growing attention to microbial communities in insects, the dynamics of psyllid microbial communities and the interactions between obligate and facultative symbionts remain unclear. My dissertation explores a variety of aspects of the psyllid microbiota, particularly the Liberibacter-Carsonella-host interface. In chapter 2, using 16S rRNA amplicon sequencing and metagenomic sequencing, I revealed potential long-term psyllid symbiont associations in the family Triozidae and Psyllidae. I have also discovered a novel Ca. Liberibacter spp., Ca. L. capsica, which is potential pathogen of solanaceous crops. These findings suggest microbiome profiling of psyllids has great potential for revealing potential risk of new pathogen development and regulatory concerns. In Chapter 3 and 4, taking advantage of the high-quality chromosomal genome assembly and transcriptomes from distantly related species, Diaphorina citri and Bactericera cockerelli, I investigated conserved and lineage-specific gene expression patterns that are related to nutritional symbioses, Carsonella. In the last part of my dissertation, I demonstrated how Ca. L. psyllaurous, and host plant use can influence the integrated metabolism of Carsonella and B. cockerelli. Ultimately, this study has yielded valuable insights that will serve as a foundation for future research on Ca. L. psyllaurous-Carsonella-psyllid interactions.