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

Michael J. Naldrett,Kyle G. Koch,Lise Pingault,Prince Zogli,Nathan A. Palmer,Gautam Sarath,Sophie Alvarez,Paul Twigg,Joe Louis,Tiffany M. Heng-Moss,Jeffrey D. Bradshaw

doi:10.1038/s41598-020-71828-8

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.

Highlights

Cereal aphids can successfully colonize and damage switchgrass (Panicum virgatum) plants[1]
To investigate the mechanisms of switchgrass responses against GB, the proteomic profiles of aphid-infested and uninfested control plants was performed on 10 days post aphid infestation (10 days post infestation (DPI)) (Fig. S1)
429 of these proteins were identified as differentially expressed proteins (DEPs) with a log[2] fold change Infected/Control (log2FC (I10/C10)) that are significantly different based on an adjusted p value ≤ 0.05 cutoff criteria (Table S2)

Summary

Introduction

Cereal aphids can successfully colonize and damage switchgrass (Panicum virgatum) plants[1]. An evaluation of switchgrass plants for categories of resistance indicated that plants of upland cultivar Summer were moderately susceptible to GB herbivory, and demonstrated responses consistent with tolerance[7]; GB could not colonize or inflict significant damage on the lowland cultivar Kanlow[8,9]. Consistent with data reported in the literature[9,10], there was a significant downregulation of genes associated with nutrient assimilation, photosynthetic pigment biosynthesis, and other growth-related pathways, and a concomitant upregulation of genes involved in plant defense and catabolic processes. Upregulation of peroxidase genes and protein activity have been frequently linked to aphid herbivory as well as to tolerant or resistant plants[15]. The general trend shown in the literature suggests that besides upregulation of stress responsive proteins, insect feeding leads to changes in plant metabolism (carbohydrate, amino acid, and energy metabolism) and photosynthesis. Other studies reported high accumulation of enzymes involved in jasmonic acid (JA) and ethylene biosynthetic pathways, as well as serine proteases/ protease inhibitors, in response to root herbivory[24]

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