Differential Defense Responses of Upland and Lowland Switchgrass Cultivars to a Cereal Aphid Pest.

Lise Pingault,Gautam Sarath,Tiffany Heng-Moss,Paul Twigg,Javier Seravalli,Jeffrey D Bradshaw,Joe Louis,Kyle G Koch,Nathan A Palmer

doi:10.3390/ijms21217966

Abstract

Yellow sugarcane aphid (YSA) (Sipha flava, Forbes) is a damaging pest on many grasses. Switchgrass (Panicum virgatum L.), a perennial C4 grass, has been selected as a bioenergy feedstock because of its perceived resilience to abiotic and biotic stresses. Aphid infestation on switchgrass has the potential to reduce the yields and biomass quantity. Here, the global defense response of switchgrass cultivars Summer and Kanlow to YSA feeding was analyzed by RNA-seq and metabolite analysis at 5, 10, and 15 days after infestation. Genes upregulated by infestation were more common in both cultivars compared to downregulated genes. In total, a higher number of differentially expressed genes (DEGs) were found in the YSA susceptible cultivar (Summer), and fewer DEGs were observed in the YSA resistant cultivar (Kanlow). Interestingly, no downregulated genes were found in common between each time point or between the two switchgrass cultivars. Gene co-expression analysis revealed upregulated genes in Kanlow were associated with functions such as flavonoid, oxidation-response to chemical, or wax composition. Downregulated genes for the cultivar Summer were found in co-expression modules with gene functions related to plant defense mechanisms or cell wall composition. Global analysis of defense networks of the two cultivars uncovered differential mechanisms associated with resistance or susceptibility of switchgrass in response to YSA infestation. Several gene co-expression modules and transcription factors correlated with these differential defense responses. Overall, the YSA-resistant Kanlow plants have an enhanced defense even under aphid uninfested conditions.

Highlights

Switchgrass (Panicum virgatum L.) cultivars originally derived from diverse native populations are genetically distinct from one another and possess significant variation in morphological and physiological traits [1,2]
No significant difference was observed in aphid numbers for the yellow sugarcane aphid (YSA)-infested Kanlow plants at all sampling time points and 5 and 10 Days After Infestation (DAI) for the cultivar Summer
Sscigi. n20if2i0c,a2n1,t7d96i6fference was observed in aphid numbers for the YSA-infested Kanlow pla3notfs2a1t all sampling time points and 5 and 10 Days After Infestation (DAI) for the cultivar Summer

Summary

Introduction

Switchgrass (Panicum virgatum L.) cultivars originally derived from diverse native populations are genetically distinct from one another and possess significant variation in morphological and physiological traits [1,2]. Switchgrass cultivars often differ in their responses to biotic and abiotic stress as well [3,4,5,6,7]. The lowland switchgrass cultivar ‘Kanlow’ had greater resistance to the generalist herbivore fall armyworm (Spodoptera frugiperda Smith.), greenbugs (GB; Schizaphis graminum Rondani), and the yellow sugarcane aphid (YSA; Sipha flava Forbes) compared to the upland cultivar ‘Summer’. The cultivar ‘Summer’ was developed from plants that originated from SE Nebraska USA, and possesses superior winter tolerance with finer tillers and narrow leaves. Whereas the cultivar ‘Kanlow’ was developed from plants collected at a lowland site in Oklahoma, USA [12]. Kanlow has superior biomass yields compared to Summer but has poorer winter survival at more norther sites of the USA [13]

Methods

Results

Discussion

Conclusion