Date of this Version
Koch, K. G. 2017. Analysis of Cereal Aphid Feeding Behavior and Transcriptional Responses Underlying Switchgrass-Aphid Interactions. PhD Dissertation. University of Nebraska-Lincoln. 1-188.
Switchgrass, Panicum virgatum L., is a perennial warm-season grass that is a model species for the development of bioenergy crops. However, the sustainability of switchgrass as a bioenergy feedstock will require efforts directed at improved biomass yield under a variety of stress factors. The objectives of this research were to: (1) elucidate greenbug and yellow sugarcane aphid feeding behavior on resistant and susceptible switchgrasses using electronic penetration graphs (EPG), (2) define transcriptional changes before and during insect feeding through RNA-seq to identify candidate resistance genes in a hybrid switchgrass cultivar, and (3) utilize methods in RNA sequencing of insects to uncover key transcriptional regulatory mechanisms involved in switchgrass-aphid interactions.
Electronic penetration graphs on V3 switchgrass corroborated previous work detailing greenbug feeding behavior on V1 grasses. Greenbugs were unable to sustain phloem ingestion on resistant Kanlow plants. However, significant differences were not documented for yellow sugarcane aphid feeding behavior on V1 and V3 switchgrass.
Transcriptional changes during insect feeding revealed that both aphids induced remodeling of the transcriptome in the hybrid switchgrass cultivar, KxS. KxS upregulated reactive oxygen species (ROS) metabolizing enzymes and downregulated genes in primary metabolism. Downregulation of genes associated with primary metabolism could effectively starve aphids of nutrients and/or direct resources to the production of defense-related metabolites. However, greenbugs and yellow sugarcane aphids induced divergent defense responses, including phytohormone signaling pathways and metabolite expression. KxS plants responded to yellow sugarcane aphid feeding, but not greenbugs, by inducing genes associated with a flavonoid biosynthesis pathway.
Characterizing the molecular response of greenbugs and yellow sugarcane aphids revealed an induction of genes associated with carbohydrate synthesis/metabolism on switchgrass, potentially to compensate for insufficient nutritional resources from the plants. Genes involved in xenobiotic metabolism were increased in aphids that had been starved or fed switchgrass, including Cytochrome P450s. Moreover, proteases were broadly induced in greenbugs that had feed on switchgrass, presumably to overcome plant protease inhibitors.
Together, these studies present critical information for improving our knowledge of the plant-aphid interactions within this system and may help in characterizing specific mechanisms of resistance.
Advisors: Tiffany Heng-Moss and Jeff Bradshaw