Endophyte Infection and Methyl Jasmonate Treatment Increased the Resistance of Achnatherum sibiricum to Insect Herbivores Independently.

Junhua Qin,Hui Liu,Man Wu,Yubao Gao,Anzhi Ren

doi:10.3390/toxins11010007

Abstract

Alkaloids are usually thought to be responsible for protecting endophyte-infected (EI) grasses from their herbivores. For EI grasses that produce few alkaloids, can endophyte infection enhance their resistance to herbivores? Related studies are limited. In the Inner Mongolian steppe, Achnatherum sibiricum is highly infected by Epichloë endophytes, but produces few alkaloids. Locusts are the common insect herbivores of grasses. In this study, A. sibiricum was used as plant material. Methyl jasmonate (MJ, when applied exogenously, can induce responses similar to herbivore damage) treatment was performed. The effects of endophyte infection and MJ treatment on the resistance of A. sibiricum to Locusta migratoria were studied. We found that locusts preferred EF (endophyte-free) plants to EI plants in both choice and no-choice feeding experiments. Endophyte infection enhanced the resistance of A. sibiricum to locusts. Endophyte infection decreased soluble sugar concentrations, while it increased the total phenolic content and phenylalanine ammonia lyase (PAL) activity, which may contribute to the resistance of A. sibiricum to locusts. There was an interaction effect between MJ treatment and endophyte infection on the growth of the host. MJ treatment was a negative regulator of the plant growth-promoting effects of endophyte infection. There was no interaction effect between MJ treatment and endophyte infection on the defense characteristics of the host. In groups not exposed to locusts, MJ treatment and endophyte infection had a similar effect in decreasing the soluble sugar content, while increasing the total phenolic content and the PAL activity. In groups exposed to locusts, the effect of MJ treatment on the above characteristics disappeared, while the effect of endophyte infection became more obvious. All of these results suggest that even for endophytes producing few alkaloids, they could still increase the resistance of native grasses to insect herbivores. Furthermore, endophyte infection might mediate the defense responses of the host, independent of jasmonic acid (JA) pathways.

Highlights

Epichloë endophyte species are characterized by their endophytic lifestyles in aerial parts of cool-season grasses [1]
In groups not exposed to locusts, Methyl Jasmonate (MJ) treatment and endophyte infection had a similar effect in decreasing the soluble sugar content, while increasing the total phenolic content and the phenylalanine ammonia lyase (PAL) activity
In the choice feeding experiment, the amount of mass consumed by L. migratoria was significantly affected by endophyte infection (F = 17.405, p < 0.01), as well as the interaction of the endophyte and MJ treatment (F = 6.841, p = 0.010)

Summary

Introduction

Epichloë endophyte species are characterized by their endophytic lifestyles in aerial parts of cool-season grasses [1]. A remarkable characteristic of many Epichloë species is their ability to produce biologically active alkaloids, which contribute to the deterrence of herbivores [12,13,14]. Alkaloids are widely distributed in endophyte-infected grasses, but their profiles and concentrations vary considerably [16,17,18]. Siegel et al surveyed 48 grass samples infected by different species of Epichloë, and they found that five symbionts had three classes of alkaloids, 19 contained two, 19 contained one, and five did not contain alkaloids [16]. Can endophyte infection enhance the herbivore deterrence of host plants that produce few alkaloids? Can endophyte infection enhance the herbivore deterrence of host plants that produce few alkaloids? The related studies are limited [19,20]

Methods

Results

Discussion

Conclusion