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. 2019 Jun 13;14(6):e0218352.
doi: 10.1371/journal.pone.0218352. eCollection 2019.

Fall armyworm (Spodoptera frugiperda Smith) feeding elicits differential defense responses in upland and lowland switchgrass

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Fall armyworm (Spodoptera frugiperda Smith) feeding elicits differential defense responses in upland and lowland switchgrass

Nathan A Palmer et al. PLoS One. .

Abstract

Switchgrass (Panicum virgatum L.) is a low input, high biomass perennial grass being developed for the bioenergy sector. Upland and lowland cultivars can differ in their responses to insect herbivory. Fall armyworm [FAW; Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae)] is a generalist pest of many plant species and can feed on switchgrass as well. Here, in two different trials, FAW larval mass were significantly reduced when fed on lowland cultivar Kanlow relative to larvae fed on upland cultivar Summer plants after 10 days. Hormone content of plants indicated elevated levels of the plant defense hormone jasmonic acid (JA) and its bioactive conjugate JA-Ile although significant differences were not observed. Conversely, the precursor to JA, 12-oxo-phytodienoic acid (OPDA) levels were significantly different between FAW fed Summer and Kanlow plants raising the possibility of differential signaling by OPDA in the two cultivars. Global transcriptome analysis revealed a stronger response in Kanlow plant relative to Summer plants. Among these changes were a preferential upregulation of several branches of terpenoid and phenylpropanoid biosynthesis in Kanlow plants suggesting that enhanced biosynthesis or accumulation of antifeedants could have negatively impacted FAW larval mass gain on Kanlow plants relative to Summer plants. A comparison of the switchgrass-FAW RNA-Seq dataset to those from maize-FAW and switchgrass-aphid interactions revealed that key components of plant responses to herbivory, including induction of JA biosynthesis, key transcription factors and JA-inducible genes were apparently conserved in switchgrass and maize. In addition, these data affirm earlier studies with FAW and aphids that the cultivar Kanlow can provide useful genetics for the breeding of switchgrass germplasm with improved insect resistance.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Bioassay and Phytohormones.
(A) FAW weight 10 dpi on Kanlow (blue) or Summer (orange) seedlings. (B) Jasmonic acid (JA) quantification in Kanlow (blue) and Summer (orange) seedlings in uninfested control and FAW infested seedlings after 10 dpi. (C) JA-Ile quantification in Kanlow (blue) and Summer (orange) seedlings in uninfested control and FAW infested seedlings after 10 dpi. (D) OPDA quantification in Kanlow (blue) and Summer (orange) seedlings in uninfested control and FAW infested seedlings after 10 dpi. Different letters above the bars indicate values that are significantly different from each other (P < 0.05; Tukey’s test). Error bars represent SEM.
Fig 2
Fig 2. Transcriptome summary.
(A) NMDS plot of all 12 RNA-Seq samples. (B) Venn diagrams showing the number of DEGs upregulated or downregulated by FAW in Kanlow and Summer switchgrass.
Fig 3
Fig 3. KEGG pathway enrichment in DEGs.
(A) KEGG pathway significantly enriched (FDR < 0.05) in gene sets upregulated by FAW in Kanlow (blue) and Summer (orange) switchgrass. If the pathway was enriched, the proportion of DEGs in the gene set relative to the total number of expressed genes in the pathway is shown on the x-axis. (B) KEGG pathway significantly enriched (FDR < 0.05) in gene sets downregulated by FAW in Kanlow (blue) and Summer (orange) switchgrass.
Fig 4
Fig 4. Meta-analysis of genes induced by insect pests.
Venn diagrams showing the overlap of DEGs in this study compared to DEGs identified in Donze-Reiner et al. [25] resulting from GB feeding on Summer switchgrass and switchgrass orthologs to DEGs identified in Tzin et al. [37] resulting from FAW feeding on Zea mays after 24 hours.

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