Aphid-responsive defense networks in hybrid switchgrass

Authors: KOCH, KYLE - University Of Nebraska; Palmer, Nathan - Nate; DONZE-REINER, TERESA - West Chester State University; Scully, Erin; SERAVALLI, JAVIER - University Of Nebraska; AMUNDSEN, KEENAN - University Of Nebraska; TWIGG, PAUL - University Of Nebraska; LOUIS, JOE - University Of Nebraska; BRADSHAW, JEFFREY - University Of Nebraska; HENG-MOSS, TIFFANY - University Of Nebraska; Sarath, Gautam

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2020
Publication Date: 7/30/2020
Citation: Koch, K.G., Palmer, N.A., Donze-Reiner, T., Scully, E.D., Seravalli, J., Amundsen, K., Twigg, P., Louis, J., Bradshaw, J.D., Heng-Moss, T., Sarath, G. 2020. Aphid-responsive defense networks in hybrid switchgrass. Frontiers in Plant Science. 11:1145. https://doi.org/10.3389/fpls.2020.01145.
DOI: https://doi.org/10.3389/fpls.2020.01145

Interpretive Summary: Switchgrass plants can belong to different adaptation types that frequently display diverse genetics and responses to pests and pathogens. The molecular defensive responses of switchgrass plants to aphids is still largely unexplored. In this study, plants derived by crossing upland and lowland adapted switchgrass plants (termed SxK) were infested with one of two aphids, greenbugs or yellow sugarcane aphids. Both aphids can colonize and damage SxK plants. SxK plants represent a unique germplasm resource for breeding improved switchgrass cultivars that are broadly adapted to the Northern Great Plains of the US. Metabolite and gene-expression combined with bioinformatic and statistical tools were used to evaluate the defense responses of SxK plants to each aphid. Analysis of data obtained showed that early plant responses to aphid herbivory were largely similar to what has been observed in other plant-aphid interactions. However, dynamic differences were seen at later sampling dates and metabolic and gene expression outcomes that were specific to either aphid were found. Other data provide several genes that could serve as markers for interrogating switchgrass lines for improved tolerance to pests and potentially pathogens.

Technical Abstract: Aphid herbivory elicits plant defense-related networks which are influenced by host genetics. Plants of the upland switchgrass (Panicum virgatum) cultivar Summer can host greenbugs (Schizaphis graminum; GB), and yellow sugarcane aphids (Sipha flava, YSA), whereas the lowland cultivar Kanlow is not a host for GB. However, stabilized hybrids of Summer (') x Kanlow (') (SxK) with improved agronomics can be damaged by both aphids. Here, hormone and metabolite analyses, coupled with RNA-seq of plant transcriptomes, were utilized to delineate defense networks of aphid-infested SxK switchgrass, and pinpoint plant transcription factors (TFs), such as WRKYs that potentially control these responses. Abscisic acid (ABA) levels were significantly higher in GB infested plants at 5 and 10 days after infestation (DAI). ABA levels increased to a maximum at 15DAI in YSA infested plants. Jasmonic acid levels were significantly elevated only under GB infestation. Salicylic acid was elevated in aphid-infested plants compared to uninfested controls, with a significant difference in levels observed at 15DAI only in YSA infested plants. Similarly, levels of several metabolites were changed in common or specifically to each aphid. YSA infestation induced a significant enrichment of flavonoids consistent with an upregulation of many genes associated with flavonoid biosynthesis at 15DAI. Gene co-expression modules that responded in common to both aphids or singly to either aphid were differentiated and linked to TFs. Together, these data provide important clues into the interplay of metabolism and transcriptional remodeling accompanying defense responses to aphid herbivory in hybrid switchgrass.