Mutualism effectiveness of a fungal endophyte in an annual grass is impaired by ozone

Abstract

1.Ozone is an increasing tropospheric contaminant of climate change. Exposure to ozone may affect the symbiotic relationship between plants and beneficial microorganisms. In particular, the herbivore resistance mechanism conferred by fungal endophytes (defensive mutualism) may be affected, as any of the ozone-triggered effects (such as elicitation of defence mechanisms against biotrophic fungi or oxidative stress in the apoplastic space) may target the symbiont. 2. Symbiotic and non-symbiotic Lolium multiflorum plants were exposed to ozone for two consecutive days (2 h per day), after which half were infested with 10 aphids (Rhopalosiphum padi). We measured variables related to performance of plants, the endophyte symbiont (alkaloids) and the herbivores. 3. Aphid populations were smaller on symbiotic plants than in non-symbiotic plants in lowozone conditions. However, this difference disappeared in exposed plants to high-ozone conditions. Under low-ozone conditions, structure of aphid populations on endophyte-symbiotic plants was characterized by a low number of nymphs and a high number of adults. This pattern was not observed with high-ozone exposure. Level of fungal alkaloids (lolines) was not affected by either ozone or herbivory. 4. Results indicate that ozone impairs the grass-endophyte symbiosis without affecting production of alkaloids generally linked with aphids' response to endophyte presence. Since neither plant biomass nor alkaloid level were affected by ozone, other ozone-mediated mechanisms at molecular or biochemical level may underlie plant-herbivore interaction mediated by fungal endophytes. Thus, the mechanism behind this effect must be determined in future experiments.

Effect of Endophyte Infection and Clipping Treatment on Resistance and Tolerance of Achnatherum sibiricum

“…However, we found that infected A. sibiricum had significant resistance to L. migratoria , which suggests that apart from endophyte-conferred alkaloid defense, additional mechanisms such as endophyte-mediated changes in host defense are likely to be implicated in endophyte-host-insect interactions. Similar results have been reported recently by Ueno et al (2016), who found that ozone level did not affect alkaloid concentration but rather significantly affected aphid resistance of infected Lolium multiflorum .…”

A fungal endophyte of a palatable grass affects preference of large herbivores

“…The infection frequency was determined by sampling 50 seeds of each population and endophyte status (high and low infection). Even though in this study we did not quantify alkaloid plant concentration, Ueno et al (2016) recently reported that plant concentration of loline derivatives (Nacetylnorloline, N-formylloline and N-acetylloline) in infected plants ranged between 200 and 300 lg g À1 of plant in this population. Positive samples showed the presence of non-branching intercellular hyphae (Bacon & White 1994).…”

“…Lucero endophyte-infected seeds were obtained from the endophytic individuals of an original population with %53% infection, and the endophyte-free seeds, from the non-infected plants of the same original population. Even though in this study we did not quantify alkaloid plant concentration, Ueno et al (2016) recently reported that plant concentration of loline derivatives (Nacetylnorloline, N-formylloline and N-acetylloline) in infected plants ranged between 200 and 300 lg g À1 of plant in this population. Feliciano endophyte-infected seeds were obtained from an original population with 100% infection, and the endophyte-free seeds, from the same original population from which the endophyte was removed by an ageing treatment.…”

“…(Italian ryegrass) and Epichlo€ e occultans does not produce harmful alkaloids to domestic herbivores (TePaske et al 1993). These types of alkaloids have not been described as toxic for cattle, but they have been described as modifiers of the preference of rodents and arthropods for infected seeds and plants (Omacini et al 2001;Uchitel et al 2011;Ueno et al 2016). populations infected with E. occultans exhibit peramines (Sugawara et al 2006), N-acetylnorlolines and N-formyllolines (Moore et al 2015) in variable concentrations according to plant organs, phenological stage and geographical origin.…”

“…populations infected with E. occultans exhibit peramines (Sugawara et al 2006), N-acetylnorlolines and N-formyllolines (Moore et al 2015) in variable concentrations according to plant organs, phenological stage and geographical origin. These types of alkaloids have not been described as toxic for cattle, but they have been described as modifiers of the preference of rodents and arthropods for infected seeds and plants (Omacini et al 2001;Uchitel et al 2011;Ueno et al 2016). Nevertheless, in addition to fungal alkaloids, several studies suggest that epichloid endophytes may exert further ecophysiological and metabolomic effects (e.g.…”