Differential defense responses of upland and lowland switchgrass cultivars to a cereal aphid pest

Authors: PINGAULT, LISE - University Of Nebraska; Palmer, Nathan - Nate; KOCH, KYLE - University Of Nebraska; HENG-MOSS, TIFFANY - University Of Nebraska; BRADSHAW, JEFFREY - University Of Nebraska; SERAVALLI, JAVIER - University Of Nebraska; TWIGG, PAUL - University Of Nebraska; LOUIS, JOE - University Of Nebraska; Sarath, Gautam

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2020
Publication Date: 10/27/2020
Citation: Pingault, L., Palmer, N.A., Koch, K.G., Heng-Moss, T.M., Bradshaw, J.D., Seravalli, J., Twigg, P., Louis, J., Sarath, G. 2020. Differential defense responses of upland and lowland switchgrass cultivars to a cereal aphid pest. International Journal of Molecular Sciences. 21(21). Article 7966. https://doi.org/10.3390/ijms21217966.
DOI: https://doi.org/10.3390/ijms21217966

Interpretive Summary: Switchgrass cultivars with diverse genetics and responses to stress are integral to the breeding of germplasm with superior agronomics. In this study, one upland cultivar ‘Summer’ and a lowland cultivar ‘Kanlow’ were evaluated for their defense responses to herbivory by the cereal pest yellow sugarcane aphid (YSA). Metabolite and gene-expression combined with bioinformatic and statistical tools were used to evaluate the defense responses of Summer and Kanlow plants to YSA. Analysis of data obtained showed that the more resistant Kanlow plants had a higher level of basal resistance and did not respond strongly to aphid infestation. The susceptible Summer plants mounted a strong defense response to YSA herbivory within 5 days of infestation. These responses increased over time in concert with plant damage. Together, these data establish a potential reason for greater resistance to YSA herbivory in Kanlow plants and provide new data on the genes and metabolites that underpin switchgrass defense responses. Some of these genes and metabolites could be exploited to improve resistance of switchgrass germplasm to aphids.

Technical Abstract: Yellow sugarcane aphid (YSA) (Sipha flava, Forbes) is a damaging pest on many grasses. Switchgrass (Panicum virgatum L.), a perennial C4 grass, has been selected as a bioenergy feedstock because of its perceived resilience to abiotic and biotic stresses. Aphid infestation on switchgrass has the potential to reduce the yields and biomass quantity. Here, the global defense response of switchgrass cultivars Summer and Kanlow to YSA feeding was analyzed by RNA-seq and metabolite analysis at 5, 10, and 15 days after infestation. Genes upregulated by infestation were more common in both cultivars compared to downregulated genes. In total, a higher number of di_erentially expressed genes (DEGs) were found in the YSA susceptible cultivar (Summer), and fewer DEGs were observed in the YSA resistant cultivar (Kanlow). Interestingly, no downregulated genes were found in common between each time point or between the two switchgrass cultivars. Gene co-expression analysis revealed upregulated genes in Kanlow were associated with functions such as flavonoid, oxidation-response to chemical, or wax composition. Downregulated genes for the cultivar Summer were found in co-expression modules with gene functions related to plant defense mechanisms or cell wall composition. Global analysis of defense networks of the two cultivars uncovered differential mechanisms associated with resistance or susceptibility of switchgrass in response to YSA infestation. Several gene co-expression modules and transcription factors correlated with these di_erential defense responses. Overall, the YSA-resistant Kanlow plants have an enhanced defense even under aphid uninfested conditions