The ultimate goal of the project is to generate soybean germplasm with superior water use efficiency that will conserve soil moisture and secure productivity if the crop becomes water limited. Most of the water taken up by plant roots is lost via transpiration from small pores in leaves named stomata. However, to capture atmospheric CO2, which is essential for photosynthesis, stomatal pores need to stay open. In this project, we propose to modify stomatal opening in a smart way which will allow to limit the water loss under water-limited conditions with minimal effect on photosynthesis and stomatal behavior under well-watered conditions. We will achieve this by modifying the light-derived signal for stomata opening through increasing the amount of the photosynthesis-related protein. Using this approach in tobacco, we reduced by a 25% the amount of water used for each molecule of CO2 assimilated by leaf and achieved higher biomass accumulation under field conditions, limiting the wildtype growth. In the first year of this three-year project, transgenic lines of soybean with drought-inducible overexpression of photosynthesis-related protein will be generated. In the FY22 and FY23, the characterization of these lines under water-limited conditions at the greenhouse and field will be performed.
(Year 3)

The ultimate goal of the project is to generate soybean germplasm with superior water use efficiency that will conserve soil moisture and secure productivity if the crop becomes water limited. Most of the water taken up by plant roots is lost via transpiration from small pores in leaves named stomata. However, to capture atmospheric CO2 which is essential for photosynthesis, stomata! pores need to stay open. In this project, we propose to modify stomata! opening in a smart way which will allow to limit the water loss under water-limited conditions with minimal effect on photosynthesis and stomata! behavior under well-watered conditions. We will achieve this by modifying the light-derived signal for stomata opening through increasing the amount of the photosynthesis-related protein. Using this approach in tobacco, we reduced by a 25% the amount of water used for each molecule of CO2 assimilated by leaf and achieved higher biomass accumulation under field conditions, limiting the wildtype growth. In the first year of this three-year project, transgenic lines of soybean with drought-inducible overexpression of photosynthesis-related protein will be generated. In the FY22 and FY23, the characterization of these lines under water-limited conditions at the greenhouse and field will be performed.

Our long-term goal is to generate soybean germplasm with superior water use efficiency that will conserve soil moisture and increase productivity if the crop becomes water limited. This three-year project will achieve two objectives. In Objective 1, which is under progress in FY21, we will produce non- segregating T2 generation of soybean lines with drought-inducible overexpression of PsbS. This will provide the foundation for our Objective 2 work in FY22 and FY23, when we will study the effects of the introduced gene on soybean growth under water-limited conditions in greenhouse and field setups.

Statement about Novelty: Manipulating chloroplast-derived signal for stomatal opening in response to light to improve water use efficiency has never been explored before in soybean. However, our preliminary results collected on tobacco provide proof of concept that, through genetic manipulation, increasing PsbS expression suppresses stomatal opening with little effect on CO2 uptake and thus increases water use efficiency. The overexpression of PsbS in response to low water availability that will be achieved with the use of the stress-inducible promoters in this project is also novel. Overexpressing the PsbS only in response to low water availability will work as an "insurance policy" against the drought related loss in yield and will not affect plants under well-watered conditions. This approach will conserve soil moisture and will result in increased productivity if the crop becomes water limited. This project has the potential to increase the yield of soybean grown in Nebraska on 2.9 million rainfed acres and improve the water use efficacy in between irrigation cycles in the remaining 2.8 million irrigated acres.
Technology Transfer: The results will be published in an academic journal and in public formats, including UNL websites and local news, to disseminate the water-saving advantages of the generated soybean lines to the public.

Low water availability limits soybean yield especially during reproduction. This project by developing and investigating the lines with genetically improved water use efficacy, offers the opportunity to create the novel soybean germplasm which will allow to secure productivity if the crop becomes water limited and reduce the need for irrigation. The genetic modification which is "switching on" only in response to low water accessibility will work as an "insurance policy" against the drought related loss in yield and will not affect plants under well-watered conditions. Successful completion of this project has potential to increase the yield of soybean grown in Nebraska on 2.9 million rainfed acres and improve the water conservation in between the irrigation cycles in the remaining 2.8 million irrigated acres.