The ultimate goal of the project is to generate soybean germplasm with superior water use efficiency that will conserve soil moisture and reduce yield loss 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 which increases conversion of energy of light into heat. Our successful test of this approach in tobacco resulted in a 25% reduction of the amount of water used for each molecule of CO2 assimilated by leaf and increase in biomass accumulation under field conditions, limiting the wild-type growth. We expect that this manipulation will also be effective in soybean since over-expressed protein and its function is universal across higher plants.

In the first year of this three-year project, transgenic lines of soybean with drought inducible over-expression of photosynthesis-related protein will be generated. The genetic modification “switching on” only in response to low water accessibility will work as an “insurance policy” against the drought related loss in yield. In the second and third year of this project, the effect of the introduced gene on soybean growth and yield under water-limited conditions in greenhouse and field setups will be evaluated. The proposed research will be the first of its kind to examine the manipulation of chloroplast derived signal for stomatal opening in response to light to improve water use efficiency in soybean.
Novel bioengineering strategies to improve soybean are urgently needed, especially considering the long timelines for developing new crop varieties. 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 soil moisture conservation in between irrigation cycles in the remaining 2.8 million irrigated acres.

Objective 1: Generate soybean lines with dought-inducible overexpression of PsbS
Objective 2: Evaluate the effect of PsbS over-expression on the growth of soybean in greenhouse and field under well-watered and water-limited conditions.

FY 2021: The constructs will be made by the end of October 2021. The transformation produced plants of the T0 generation will be obtained in May 2022. The propagation of T0 plants to next generations, along with segregation for homozygosity and functionality of the introduced T-DNA, will be conducted in the third and fourth quarters. Selected homozygous T1 plants will be grown to T2 seeds which will be harvested in November 2022. FY 2022: Evaluation of all generated T2 lines for drought inducible over-expression of PsbS and water savings under drought conditions in greenhouse settings will be conducted in the first and second quarter. FY 2022 and FY 2023: The physiological, molecular, and growth characterization of selected T2 lines under controlled and drought conditions in greenhouse settings will be conducted in the second and third quarters of FY 2022 and FY 2023 while the field setting characterizations will be conducted in the third and fourth quarters of FY 2022 and FY 2023.

Low water availability limits soybean yield especially during reproduction. By developing and investigating the lines with genetically improved water use efficacy, this project 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 betwwn the irrigation cycles in the remaining 2.8 million irrigated acres.