Greenbug (Schizaphis graminum) herbivory significantly impacts protein and phosphorylation abundance in switchgrass (Panicum virgatum)

Authors: ZOGLI, PRINCE - University Of Nebraska; ALVAREZ, SOPHIE - University Of Nebraska; NALDRETT, MICHAEL - University Of Nebraska; Palmer, Nathan - Nate; KOCH, KYLE - University Of Nebraska; PINGAULT, LISE - University Of Nebraska; BRADSHAW, JEFFREY - University Of Nebraska; TWIGG, PAUL - University Of Nebraska; HENG-MOSS, TIFFANY - University Of Nebraska; LOUIS, JOE - University Of Nebraska; Sarath, Gautam

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2020
Publication Date: 9/9/2020
Citation: Zogli, P.K., Alvarez, S., Naldrett, M.J., Palmer, N.A., Koch, K.G., Pingault, L., Bradshaw, J.D., Twigg, P., Heng-Moss, T., Louis, J., Sarath, G. 2020. Greenbug (Schizaphis graminum) herbivory significantly impacts protein and phosphorylation abundance in switchgrass (Panicum virgatum). Scientific Reports. 10:14842. https://doi.org/10.1038/s41598-020-71828-8.
DOI: https://doi.org/10.1038/s41598-020-71828-8

Interpretive Summary: Switchgrass plants can mount a robust defense against aphid herbivores. These defenses have been studied earlier at the gene-expression level. In this current work, the global changes in proteins extracted from switchgrass cultivar Summer plants challenged with the cereal aphid, greenbugs, were analyzed using mass spectrometric methods. Analysis of data indicated that many proteins associated with plant defense responses were induced in plants attacked by greenbugs relative to control plants that were not infested. Similarly, levels of several proteins involved with photosynthesis were reduced upon aphid feeding, confirming observations across several other plant-aphid interactions. Phosphorylation of proteins, which is an integral means by which protein activity in cells is controlled, were also differentially affected by greenbug herbivory. Together the data documenting changes in protein abundance and protein phosphorylation levels corroborated earlier studies done on switchgrass-aphid interactions. This new information on proteins whose abundances changed significantly provided targets that will be useful for interrogating switchgrass lines for improved tolerance to pests and potentially pathogens.

Technical Abstract: Switchgrass (Panicum virgatum L.) is an important crop for biofuel production but it also serves as host for greenbugs (Schizaphis graminum Rondani; GB). Although transcriptomic studies have been done to infer the molecular mechanisms of plant defense against GB, little is known about the effect of GB infestation on the switchgrass protein expression and phosphorylation regulation. The global response of the switchgrass cultivar Summer proteome and phosphoproteome was monitored by label-free proteomics shotgun in GB-infested and uninfested control plants at 10 days post infestation. Peptides matching a total of 3,594 proteins were identified and 429 were differentially expressed proteins in GB-infested plants relative to uninfested control plants. Among these, 291 and 138 were up and downregulated by GB infestation, respectively. Phosphoproteome analysis identified 310 differentially phosphorylated proteins (DP) from 350 phosphopeptides with a total of 399 phosphorylated sites. These phosphopeptides had more serine phosphorylated residues (79%), compared to threonine phosphorylated sites (21%). Overall, KEGG pathway analysis revealed that GB feeding led to the enriched accumulation of proteins important for biosynthesis of plant defense secondary metabolites and repressed the accumulation of proteins involved in photosynthesis. Interestingly, defense modulators such as terpene synthase, papain-like cysteine protease, serine carboxypeptidase, and lipoxygenase2 were upregulated at the proteome level, corroborating previously published transcriptomic data.