Although all plants in natural ecosystems have symbiotic associations with endophytic fungi, the role these fungal symbionts play in ecosystem dynamics is poorly understood. The time frame required for plant adaptation to environmental stresses is unknown, but, the adaptive process is considered to be regulated by the plant genome. However, most plant studies do not consider the potential contribution of fungal symbionts to plant adaptation. Previous studies indicated that fitness benefits conferred by symbiotic fungi contribute to and are responsible for plant adaptation to high stress environments. In addition, recent findings indicate that plants change endophytes, and endophytes change plant hosts, in adjacent microhabitats that impose different selective pressures, a phenomenon described here as symbiotic modulation. Symbiotic modulation is proposed as a novel mechanism that allows plants and fungi to make quantum evolutionary jumps resulting in rapid adaptation to environmental stresses and habitat expansion. Symbiotic modulation will be studied in two locations (geothermal soils of Yellowstone National Park and costal beaches of San Juan Island) where in adjacent microhabitats imposing different selective pressures: 1) a plant host has changed endophytes; and 2) an endophyte has changed plant hosts. In both of these environments, plants are exposed to annual dry periods and either temperature or salinity stress, while adjacent microhabitats do not impose temperature or salinity stress. The proposed studies would address fundamental questions regarding the role of fungal endophytes in the adaptation of plants to: 1) elevated soil temperatures of geothermal soils and 2) high salinity of costal beaches. The objective is to determine the significance of symbiotic modulation in the expansion of plants and endophytes into new habitats, and the following hypotheses will be tested during these studies :H1 - Symbiotic modulation allows plants to adapt to high stress environments; H2 - Symbiotic modulation provides plants and fungi a mechanism to expand habitat range. To accomplish this, experiments will be performed to: 1) assess intra-species genetic diversity of fungal endophytes and plant hosts representing symbioses in two high stress habitats, 2) use the tomato model to determine if multiple mutualistic benefits can be conferred to a single host via co-colonization with endophytes that confer different stress tolerances, 3) determine if there is competition between endophytes in planta, 4) compare the physiological response to stress in symbiotic and non-symbiotic native species and tomato. The methods employed will include field, greenhouse, and growth chamber studies to characterize the ecological significance of symbiotic modulation. Native plants from two high-stress habitats and the model plant tomato will be used to characterize physiological responses to different fungal endophytes. The broader impacts are improved understanding of plant - stress tolerance, with results relevant to those interested in ecology and agriculture. Outreach with Yellowstone National Park staff is planned.
