Search

Tropospheric ozone is an abiotic stress of increasing importance in the context of global climate change. This greenhouse gas is a potent phytotoxic molecule with demonstrated negative effects on crop yield and natural ecosystems. Recently, oxidative stress has been proposed as a mechanism that could regulate the interaction between cool‐season grasses and Epichloë endophytes. We hypothesized that exposure of Lolium multiflorum plants, hosting endophytes to an ozone‐polluted environment at different ontogenetic phases, would impact the trans‐generational dynamics of the vertically transmitted fungal symbiont. Here, we found that the ozone‐induced stress on the mother plants did not affect the endophyte vertical transmission but it impaired the persistence of the fungus in the seed exposed to artificial ageing. Endophyte longevity in seed was reduced by exposure of the mother plant to ozone. Although ozone exposure did not influence either the endophyte mycelial concentration or their compound defences (loline alkaloids), a positive correlation was observed between host fitness and the concentration of endophyte‐derived defence compounds. This suggests that fungal defences in grass seeds were not all produced in situ but remobilized from the vegetative tissues. Our study reveals ozone trans‐generational effects on the persistence of a beneficial symbiont in a host grass. Mother plant exposure to ozone did not affect the growth and the transmission of fungal endophytes into host seeds. Seed alkaloid concentration correlated with endophyte mycelial concentration and host fitness. However, ozone‐induced stress on mother plants did impair the longevity of the endophytes in the seeds. [ABSTRACT FROM AUTHOR]

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., 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., Aphid populations were smaller on symbiotic plants than in non-symbiotic plants in low-ozone 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., 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. [ABSTRACT FROM AUTHOR]

Symbiosis between cool-season grasses and vertically transmitted fungal endophytes are common and significantly impact on ecosystem function. This makes the understanding of the underlying mechanisms to symbiotic individuals frequency in local populations much more interesting. Most studies have been focused on the differential fitness between symbiotic and non-symbiotic counterparts (relative fitness), barely considering other mechanisms. We performed a microcosms experiment to evaluate whether grazing alters the dynamics of the endophyte Neotyphodium occultans in the annual grass Lolium multiflorum by simultaneously modifying the relative fitness and the endophyte efficiency to be transmitted from host plants to seeds. Grazing was simulated by means of clipping and trampling on symbiotic and non-symbiotic plants growing separately, in soils obtained from paddocks, differing in their agronomic management history (natural grassland vs. ryegrass promotion). Seed production showed a complex pattern as it depended on the symbiotic status of the plants, the level of grazing and the agro-ecological context. Grazed plants produced three times fewer seeds than ungrazed plants only in microcosms with endophyte-symbiotic plants in soils from ryegrass promotion. Endophyte benefits on seed production were exclusively observed in ungrazed plants in the same soil. Symbiotic plants produced symbiotic and non-symbiotic seeds in all the treatments. While the production of non-symbiotic seeds by these plants was not affected by grazing and the soil, grazing reduced the production of symbiotic seeds in both contexts. Grazing negative effect on the density of fully infected spikes determined a significant increment in the transmission failures which were not modified by agro-ecological contexts. Therefore, grazing can modulate symbiosis dynamics through reducing seed production and endophyte transmission efficiency. Transmission has been disregarded, but it is a context-dependent process that could lead to a gradual reduction in the symbiotic plants frequency in a population if the mutualism effectiveness does not outweigh transmission failures. [ABSTRACT FROM AUTHOR]

Simple Summary: Global change is driving the incidence of novel stress factors such as the tropospheric pollutant ozone. Plants can overcome the environmental challenges by adjusting their phenotypes that eventually, can be transmitted to the progeny. Plants also establish symbiotic interactions with beneficial fungal endophytes, some of which can be transmitted to the progeny through the seeds. We worked with the grass Lolium multiflorum and its common endophyte, Epichloë occultans that benefits the host by coffering resistance to herbivores. Specifically, we studied the effect of exposing endophyte-symbiotic and non-symbiotic plants to ozone on the level of resistance to herbivorous aphids in the progeny. The ozone history impaired the endophyte-conferred resistance to aphids in progeny. This was evident at individual weight level of aphids but not so at population level. Defensive compounds were higher in endophyte-symbiotic seeds but depressed by mother plants exposure to ozone. Despite the negative effect of maternal ozone on the resistance level of plants, symbiotic plants showed a superior biomass compared to endophyte-free plants. Our work illustrates how the environment explored by parent plants can persist transgenerationally and, depending on the symbiotic state, will affect the fate of the progeny. Plants are challenged by biotic and abiotic stress factors and the incidence of one can increase or decrease resistance to another. These relations can also occur transgenerationally. For instance, progeny plants whose mothers experienced herbivory can be more resistant to herbivores. Certain fungal endophytes that are vertically transmitted endow plants with alkaloids and resistance to herbivores. However, endophyte-symbiotic plants exposed to the oxidative agent ozone became susceptible to aphids. Here, we explored whether this effect persists transgenerationally. We exposed Lolium multiflorum plants with and without fungal endophyte Epichloë occultans to ozone (120 or 0 ppb), and then, challenged the progeny with aphids (Rhopalosiphum padi). The endophyte was the main factor determining the resistance to aphids, but its importance diminished in plants with ozone history. This negative ozone effect on the endophyte-mediated resistance was apparent on aphid individual weights. Phenolic compounds in seeds were increased by the symbiosis and diminished by the ozone. The endophyte effect on phenolics vanished in progeny plants while the negative ozone effect persisted. Independently of ozone, the symbiosis increased the plant biomass (≈24%). Although ozone can diminish the importance of endophyte symbiosis for plant resistance to herbivores, it would be compensated by host growth stimulation. [ABSTRACT FROM AUTHOR]