Aphid-Responsive Defense Networks in Hybrid Switchgrass.

Kyle G Koch,Nathan A Palmer,Teresa Donze-Reiner,Tiffany Marie Heng-Moss,Gautam Sarath,Paul Twigg,Jeffrey D Bradshaw,Javier Seravalli,Joe Louis,Keenan Amundsen,Erin D Scully

doi:10.3389/fpls.2020.01145

Abstract

Aphid herbivory elicits plant defense-related networks that are influenced by host genetics. Plants of the upland switchgrass (Panicum virgatum) cultivar Summer can be a suitable host for greenbug aphids (Schizaphis graminum; GB), and yellow sugarcane aphids (Sipha flava, YSA), whereas the lowland cultivar Kanlow exhibited multi-species resistance that curtails aphid reproduction. 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 analysis of plant transcriptomes, were utilized to delineate defense networks induced by aphid feeding in SxK switchgrass and pinpoint plant transcription factors (TFs), such as WRKYs that potentially regulate these responses. Abscisic acid (ABA) levels were significantly higher in GB infested plants at 5 and 10 days after infestation (DAI). ABA levels were highest at 15DAI in YSA infested plants. Jasmonic acid levels were significantly elevated under GB infestation, while salicylic acid levels were signifi40cantly elevated only at 15 DAI in YSA infested plants. Similarly, levels of several metabolites were altered 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 singly to either aphid or in common to both aphids were differentiated and linked to specific TFs. Together, these data provide important clues into the interplay of metabolism and transcriptional remodeling accompanying defense responses to aphid herbivory in hybrid switchgrass.

Highlights

Insect herbivores can impose significant costs to plant fitness (Zust and Agrawal, 2017; Nalam et al, 2019)
Plants infested with GB were damaged by 5 days after infestation (5DAI) and damage ratings increased to 2.8 ± 0.1 by 10DAI and remained essentially unchanged at 15DAI
For YSA infested plants, damage ratings did not differ from control plants at 5DAI (1.3 ± 0.1) but increased significantly to 2.7 ± 0.2, by 15DAI (Figure 1B)

Summary

Introduction

Insect herbivores can impose significant costs to plant fitness (Zust and Agrawal, 2017; Nalam et al, 2019). Aphids are especially important plant pests that often have broad host ranges and significantly reduce growth/yields of susceptible plants via nutrient depletion and feeding damage to host tissues (Smith and Chuang, 2014). Aphid feeding triggers host defense responses arising from mechanical stimuli, plant tissue damage, salivary secretions, and removal of nutrients (Kindt et al, 2006; Zust and Agrawal, 2016). Much progress has been made in understanding the host defensive-networks underlying responses to aphids in model systems (Nguyen et al, 2016; Zust and Agrawal, 2017), there is still a significant lack of data on insect herbivore interactions with nonmodel plants and host signaling networks that influence defense responses at later stages of aphid infestation. Aphids can modulate plant defensive responses by secreting elicitors and proteins that improve their survival (Kaloshian and Walling, 2016)

Methods

Results

Conclusion