High temperature stress severely limits plant productivity and causes extensive economic loss to US agriculture. The negative impact of heat stress on yield stability and agricultural production has been exacerbated in recent years, and what is predicted for the future from climate change models is even more alarming. Hence, understanding the mechanisms of crop response to heat stress is critical to sustain agricultural production. Little progress has been made in this area, however, primarily due to the challenge of having access to field-based heat stress conditions, the complexity of the crop genomes, and the inadequate integration of physiology and genetics research. Without dedicated effort in advancing research in heat stress response in crops, we are certainly ill-prepared for global warming and climate change, which have shown the impact of climatological extremes, including high temperature stress, on agriculture production.The overarching rationale of the proposed research is to fill a critical research gap in understanding the mechanisms of crop response to abiotic stress, specifically heat stress response in maize. The first objective is to quantify the natural variation in heat stress response across a diverse set of maize inbred lines and identify underlying mechanisms through integrating analysis at the gene-expression, biochemical, and whole-plant level. To achieve this goal, we plan to conduct genome-wide gene expression profiling through of a set of diverse maize accessions that have been identified from extensive field screening. The second objective is to identify the genes that contribute to the differential heat stress response through joint analysis of two populations. Two mapping populations will be developed through the doubled haploid process, and field-based phenotyping and subsequent genetic mapping will be conducted.This project is designed to obtain a much improved understanding of heat stress by integrating biochemical and whole-plant characterization with molecular mechanisms. Knowledge generated from this project is expected to facilitate further breeding research in not only maize, but also many other crops. The societal benefit of this project is its scientific contribution to the sustainable agriculture production under changing climates.