Glutaredoxins (GRXs) are small ubiquitous oxidoreductase stress responsive genes, involved in floral development signaling and known to enhance tolerance to abiotic stress during reproductive development, by detoxifying the reactive oxygen species (ROS). Ectopic expression of Arabidopsis glutaredoxin gene (AtGRXS17) in maize substantially increased kernel-set and yield under heat stress (37°C daytime) both in greenhouse and field conditions. Similarly, Dr. Park and his team have engineered the cultivar ‘Thorne’, [maturity group 3, developed in the 90’s from Illinois], aimed at inducing tolerance to drought and heat stress at reproductive and pod-filling stages by overexpressing the same AtGRXS17 in soybean. Three AtGRXS17-overexpressing soybean lines showed significantly higher seed-set and seed-weight under heat stress in greenhouse conditions, compared to wild-type. Hence, the major objective of the proposed project is to characterize the effectiveness of AtGRXS17-expressing soybean transformants on seed numbers and weight and seed quality under drought, heat and combined heat and drought stress using field-based heat tents and controlled-environment facilities. Progress achieved will allow for developing gene based breeder friendly molecular markers that can be utilized across US soybean breeding programs, irrespective of maturity group.

1. Evaluate the mechanistic basis of genetically engineered soybean lines exposed to drought and heat stress during flowering and pod-filling stages, using controlled and field-based facilities
2. Ascertain the differential level of stress alleviation during the flowering and pod-filling stages in terms of yield and quality (protein, oil and oleic acid)

Project deliverables
1. Proportion of drought and heat stress damage alleviated through the engineered line quantified under field and controlled environment conditions
2. Role of the gene in improving bean quality under heat and drought stress conditions evaluated
3. Post validation, incorporation of the trait into mainstream breeding explored

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The majority of the Kansas soybean growing areas are frequently exposed to harsh environments (drought and heat stress) during the reproductive and pod-filling stages, reducing yields and quality, resulting in significant economic loss to Kansas farmers. Expansion of the soybean production area in Kansas will most inevitably be challenged by either drought, heat stress or a combination of both, particularly during the reproductive and pod-filling stages. Soybean breeding programs are successful in increasing yield potential under favorable environments, and the United Soybean Board supports two large scale abiotic stress projects that include improving drought tolerance. However, those efforts focus on using the natural genetic variability in soybean to improve tolerance. This proposal presents a different approach that could complement the current breeding efforts to help minimize drought and heat stress-induced yield and quality losses, leading to higher economic returns to soybean growers.