|KOCH, KYLE - University Of Nebraska|
|Palmer, Nathan - Nate|
|HENG-MOSS, TIFFANY - University Of Nebraska|
|BRADSHAW, JEFFREY - University Of Nebraska|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2019
Publication Date: 8/3/2019
Citation: Koch, K.G., Scully, E.D., Palmer, N.A., Geib, S.M., Sarath, G., Heng-Moss, T., Bradshaw, J.D. 2019. Divergent switchgrass cultivars modify cereal aphid transcriptomes. Journal of Economic Entomology. 112(4):1887-1901. https://doi.org/10.1093/jee/toz053.
Interpretive Summary: Switchgrass is an important bioenergy crop that can be colonized by aphids. Aphid herbivory has the potential to cause losses to biomass yields and quality. Previous studies have shown that two common cereal aphid pests, namely greenbug aphids and yellow sugarcane aphids, can feed damage, and multiply on switchgrass plants. Although greenbug aphids can colonize and damage a susceptible switchgrass cultivar (Summer), they cannot establish on a resistant switchgrass cultivar (Kanlow). In contrast, the yellow sugarcane aphid can colonize both switchgrass cultivars, but fare better on Summer. In order to identify differences in stress responses between these two aphid species that could enable yellow sugarcane aphid to establish on Kanlow, global gene expression analyses were performed on both aphids after feeding on Summer and Kanlow switchgrass and were compared to those that had fed on sorghum (BCK60), which is a highly susceptible sorghum host. Overall, both aphids responded strongly to feeding in switchgrass by expressing a high number of genes that have been linked to the degradation of toxins. However, when feeding in Kanlow, it was unable to sustain high expression levels of many of these genes, which could impact its ability to detoxify plant defensive toxins produced by this host. In contrast, S. flava was able to sustain a high level of expression of genes coding for detoxification enzymes while feeding on both Kanlow and Summer, which could allow it to successfully feed on both switchgrass cultivars. These results will be useful to the future study of these aphid pests, as well as developing switchgrass germplasm with improved resistance to aphid herbivory.
Technical Abstract: Schizaphis graminum and Sipha flava are two common pests of bioenergy grasses that have broad host ranges. Despite the fact that they are both considered generalists, they differ in their ability to colonize upland Summer and lowland Kanlow switchgrass cultivars (Panicum vigratum). S. flava colonizes both Summer and Kanlow whereas S. graminum can only colonize Summer; however, although S. flava can colonize Kanlow, it performs better on Summer, indicating a potential antibiosis effect. To study the molecular responses of these aphids to these two divergent switchgrass cultivars, we generated de novo transcriptome assemblies of both aphids and compared their transcriptional responses to starvation and feeding both Summer and Kanlow to transcriptome profiles associated with feeding on a highly susceptible sorghum host (BCK60). Transcriptome assemblies yielded, 8,428 and 8,866 high-quality unigenes for S. graminum and S. flava respectively. Overall, S. graminum responded strongly to each of the three treatments after 12 hr with an upregulation of unigenes coding for detoxification enzymes while major transcriptional changes in any of the three treatments were not observed in S. flava until 24 hr. Additionally, while the two aphids responded to both the starvation and switchgrass feeding treatment by upregulating genes linked to carbohydrate metabolism and downregulating genes linked to growth and development, the responses of the two aphids to Summer and Kanlow diverged significantly, especially with regards to the expression of unigenes coding detoxification enzymes. S. graminum upregulated more unigenes coding for stress responsive enzymes in the Summer treatment compared to S. flava; however, many of these unigenes were actually downregulated in the Kanlow treatment. In contrast, S. flava appeared capable of overcoming host-induced effects by upregulating a larger number of DEUs coding for detoxification enzymes in the Kanlow treatment ascribable to a stress response. Overall, these findings at the transcriptome-level provide data consistent with previous studies on the interactions of these two cereal aphids to divergent switchgrass hosts.