Growth enhancement and drought tolerance of hybrid poplar upon inoculation with endophyte consortia

With increasing effects of global climate change, there is a strong interest in developing biofuels from trees such as poplar (Populus sp.) that have high C sequestration rates and relatively low chemical inputs. Using plant-microbe symbiosis to maximize plant growth and increase host stress tolerance may play an important role in improving the economic viability and environmental sustainability of poplar as a feedstock. Based on our previous research, a total of ten endophyte strains were selected as a consortium to investigate the effects of inoculation on commercial hardwood cuttings of Populus deltoides x P. nigra clone OP-367. After one and a half months of growth under non-stress conditions followed by one month under water stress, there was substantial growth promotion with improved leaf physiology of poplar plants in response to the endophyte inoculation. Furthermore, inoculated plants demonstrated reduced damage by reactive oxygen species (ROS) indicating a possible mechanism for symbiosis-mediated drought tolerance. Production of important phytohormones by these endophytes and identification of microbial genes involved in conferring drought tolerance suggests their potential roles in the modulation of the plant host stress response.Fil: Khan, Zareen. University of Washington; Estados UnidosFil: Rho, Hyungmin. University of Washington; Estados UnidosFil: Firrincieli, Andrea. Università degli Studi della Tuscia; ItaliaFil: Hung, Shang Han. University of Washington; Estados UnidosFil: Luna, Maria Virginia. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Investigaciones Agrobiotecnologicas. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones Agrobiotecnologicas.; ArgentinaFil: Masciarelli, Oscar Alberto. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Ciencias Naturales; ArgentinaFil: Kim, Soo-Hyung. University of Washington; Estados UnidosFil: Doty, Sharon L.. University of Washington; Estados Unido

Salicaceae Endophyte Impacts on Physiological Functions of Host Plants: Water Relations, Photosynthesis, and Respiration in Rice (Oryza sativa)

Thesis (Ph.D.)--University of Washington, 2018Endophytes are bacteria, fungi, and yeast that live inside plants. Endophytes provide fitness benefits to the host plant while receiving carbohydrates in return. A wide range of bacteria and yeast endophyte strains was isolated from native Salicaceae trees growing in a riparian area. Previous studies on these Salicaceae endophyte isolates have shown their symbiotic traits in various host crops across taxa. Biological di-nitrogen fixation, phytohormone production, and an enhancement of drought stress tolerance in plants were important beneficial functions of these endophyte isolates. However, their impacts on the physiology of the host plant had not been examined in-depth. The focus of the present study was on water relations, photosynthesis, and respiration of the host plant to better understand symbiotic associations in the plant eco-physiological context. Select Salicaceae diazotrophic endophytes were inoculated into rice as a model C3 plant, and the effects on the physiology were assessed in a series of greenhouse experiments. The inoculated plants showed reduced stomatal conductance in the afternoon than control plants. Stomatal density of the inoculated plants was also lower than that of control plants. The accumulation of leaf ABA during the afternoon was facilitated in the inoculated plants. The stomatal responses of the inoculated plants led to decreases in transpiration, and further to increases in water use efficiency of the plants. The endophyte inoculation alleviated down-regulation of the host plant photosynthesis to elevated CO2. Moreover, the inoculated plants showed the improvements in photosynthesis compared to control plants. The improvements featured increases in electron transport rate of the photosynthetic light reactions and increases in internal CO2 conductance of the CO2 diffusion pathways in leaves. The inoculated plants showed increases in respiration rates. In vitro respiration rates of the microbes were positively correlated to the concentrations of carbohydrate supply and the number of the microbes on growing media. The in planta and the in vitro assay results provided an estimation of microbial respiratory CO2 release in the host plant. The estimate was approximately 15% of total assimilated CO2 through photosynthesis. This suggests microbial respiratory CO2 could be a significant amount and possibly reenter the photosynthetic CO2 assimilatory pathways. The stomatal closure, the photosynthetic improvements, and the respiration responses together imply the possibility of the re-assimilation and partially explain the increases in water use efficiency of the plant. Further investigation will be required to confirm the re-assimilation hypothesis with convincing empirical evidence. The key to uncover future significant findings will be an understanding of source-sink relations and carbon-nitrogen relations in plants with endophytes – the resource exchanges between the host plant and endophytes

Salicaceae Endophytes Modulate Stomatal Behavior and Increase Water Use Efficiency in Rice

Bacterial and yeast endophytes isolated from the Salicaceae family have been shown to promote growth and alleviate stress in plants from different taxa. To determine the physiological pathways through which endophytes affect plant water relations, we investigated leaf water potential, whole-plant water use, and stomatal responses of rice plants to Salicaceae endophyte inoculation under CO2 enrichment and water deficit. Daytime stomatal conductance and stomatal density were lower in inoculated plants compared to controls. Leaf ABA concentrations increased with endophyte inoculation. As a result, transpirational water use decreased significantly with endophyte inoculation while biomass did not change or slightly increased. This response led to a significant increase in cumulative water use efficiency at harvest. Different endophyte strains produced the same results in host plant water relations and stomatal responses. These stomatal responses were also observed under elevated CO2 conditions, and the increase in water use efficiency was more pronounced under water deficit conditions. The effect on water use efficiency was positively correlated with daily light integrals across different experiments. Our results provide insights on the physiological mechanisms of plant-endophyte interactions involving plant water relations and stomatal functions

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<p>Bacterial and yeast endophytes isolated from the Salicaceae family have been shown to promote growth and alleviate stress in plants from different taxa. To determine the physiological pathways through which endophytes affect plant water relations, we investigated leaf water potential, whole-plant water use, and stomatal responses of rice plants to Salicaceae endophyte inoculation under CO₂ enrichment and water deficit. Daytime stomatal conductance and stomatal density were lower in inoculated plants compared to controls. Leaf ABA concentrations increased with endophyte inoculation. As a result, transpirational water use decreased significantly with endophyte inoculation while biomass did not change or slightly increased. This response led to a significant increase in cumulative water use efficiency at harvest. Different endophyte strains produced the same results in host plant water relations and stomatal responses. These stomatal responses were also observed under elevated CO₂ conditions, and the increase in water use efficiency was more pronounced under water deficit conditions. The effect on water use efficiency was positively correlated with daily light integrals across different experiments. Our results provide insights on the physiological mechanisms of plant-endophyte interactions involving plant water relations and stomatal functions.</p