Endophytic Fungi Activated Similar Defense Strategies of Achnatherum sibiricum Host to Different Trophic Types of Pathogens

Abstract

It is well documented that Epichloë endophytes can enhance the resistance of grasses to herbivory. However, reports on resistance to pathogenic fungi are limited, and their conclusions are variable. In this study, we chose pathogenic fungi with different trophic types, namely, the biotrophic pathogen Erysiphales species and the necrotrophic pathogen Curvularia lunata, to test the effects of Epichloë on the pathogen resistance of Achnatherum sibiricum. The results showed that, compared to Erysiphales species, C. lunata caused a higher degree of damage and lower photochemical efficiency (Fv/Fm) in endophyte−free (E−) leaves. Endophytes significantly alleviated the damage caused by these two pathogens. The leaf damaged area and Fv/Fm of endophyte−infected (E+) leaves were similar between the two pathogen treatments, indicating that the beneficial effects of endophytes were more significant when hosts were exposed to C. lunata than when they were exposed to Erysiphales species. We found that A. sibiricum initiated jasmonic acid (JA)−related pathways to resist C. lunata but salicylic acid (SA)-related pathways to resist Erysiphales species. Endophytic fungi had no effect on the content of SA but increased the content of JA and total phenolic compounds, which suggest that endophyte infection might enhance the resistance of A. sibiricum to these two different trophic types of pathogens through similar pathways.

Fungal endophytes can eliminate the plant growth–defence trade‐off

“…The induction of host plant defences by Epichloë and the production of nonalkaloid compounds with putative biological activity (e.g. epichloëcyclins) could complement the resistance provided by Epichloë ‐derived alkaloids (Pańka et al ., 2013; Johnson et al ., 2015; Shi et al ., 2020). For example, L. perenne plants associated with E. festucae var.…”

“…For example, L. perenne plants associated with E. festucae var. lolii increased the plant concentration of protective phenolic compounds, which seemed to enhance the plant’s resistance against Fusarium poae (Pańka et al ., 2013; see also Shi et al ., 2020). Plant tolerance to herbivory is an alternative defence mechanism to plant resistance (yet not mutually exclusive).…”

“…By contrast, Epichloë spp. had no effect on the SA content but increased JA and total phenolic compounds in Achnatherum sibiricum plants (Shi et al ., 2020). Suppression of the SA pathway by Epichloë spp.…”

The Plant Salicylic Acid Signalling Pathway Regulates the Infection of a Biotrophic Pathogen in Grasses Associated with an Epichloë Endophyte

“…These fungal symbionts complement host plant defences by producing bioactive alkaloids that confer protection against a broad range of vertebrate and invertebrate herbivores [ 8 , 9 ]. Additionally, it has been recently reported that Epichloë symbionts can also induce the activation of plant SA and/or JA signalling pathways [ 10 , 11 ]. The activation of these plant defensive signalling pathways by beneficial symbionts can sometimes increase the levels of resistance of plants against certain attackers, including pathogens [ 6 , 11 , 12 ].…”

“…Additionally, it has been recently reported that Epichloë symbionts can also induce the activation of plant SA and/or JA signalling pathways [ 10 , 11 ]. The activation of these plant defensive signalling pathways by beneficial symbionts can sometimes increase the levels of resistance of plants against certain attackers, including pathogens [ 6 , 11 , 12 ].…”