Title: Down the rabbit-hole: origins and co-evolution of obligate bacterial symbioses in plant-sap feeding leafhoppers (Hemiptera: Cicadellidae).
The Auchenorrhyncha (Hemiptera) established obligate symbioses with bacteria ~300 million years ago [MYA]. Specific bacteria provide essential nutrition (e.g., amino acids and vitamins) absent in their hosts’ plant-sap diets. However, symbionts lose ~90% of their genes due to their permanent intracellular lifestyle. In order to function, bacteria require significant resources from their hosts. Yet symbiont origins, and the host-derived mechanisms that support them, have remained poorly understood for many insect groups. Research in my lab has revealed that although the Auchenorrhyncha split early during its diversification (>250 MYA) into the Fulgoroidea (planthoppers) and Cicadomorpha (leafhoppers and cicadas), many descendent species share two ancient symbiont lineages, Sulcia and a Betaproteobacteria (e.g., described as Nasuia in leafhoppers, Vidania in planthoppers, and Zinderia in spittlebugs). In each case, bacterial partners collaboratively provide their hosts with the 10 essential amino acids that all animals require. However, in leafhoppers, Sulcia and Nasuia have two of the smallest and most degraded bacterial genomes known. They further differ widely in their basic genetic and cellular capabilities. Thus, to individually prop up each bacterium, leafhoppers evolved distinct and precise mechanisms of support. Leafhopper hosts differentially express thousands of genes in symbiont-containing organs to meet the specific needs of each symbiont, including metabolite provisioning and support of essential cellular processes. Many of these genetic mechanisms are derived from the evolution of novel functional traits via horizontally transferred genes to the host genome, reassigned mitochondrial support genes, and gene-family duplications. Comparison across hemipteran lineages reveals that the origins of these support mechanisms are generally specific to host–symbiont systems.
Monday, February 11 at 4:10pm to 5:00pm
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