** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** SOYBEAN IS THE MOST IMPORTANT OILSEED AND ONE OF THE MOST IMPORTANT AND AFFORDABLE PROTEIN SOURCES WORLDWIDE. HIGH TEMPERATURE IS A MAJOR FACTOR LIMITING SOYBEAN YIELD. INCOMPLETE KNOWLEDGE OF THE MOLECULAR CHANGES UNDERLYING SOYBEAN HEAT TOLERANCE HAS HINDERED PROGRESS IN DEVELOPING HEAT-TOLERANT VARIETIES FOR SUSTAINABLE PRODUCTION. THE GOALS OF THE PROPOSED PROJECT ARE TO IDENTIFY SOYBEAN GENES ASSOCIATED WITH LIPID METABOLIC CHANGES AND WITH PHYSIOLOGICAL MECHANISMS CONTRIBUTING TO HEAT TOLERANCE AND TO DEVELOP MOLECULAR MARKERS FOR HIGH-THROUGHPUT SCREENING OF LARGE GERMPLASM COLLECTIONS FOR HEAT TOLERANCE. THE SPECIFIC OBJECTIVES OF THE PROJECT ARE TO (1) CHARACTERIZE THE HEAT TOLERANCE OF MEMBERS OF A SOYBEAN RECOMBINANT INBRED LINE POPULATION (DERIVED FROM A GENETIC CROSS BETWEEN A HEAT-TOLERANT AND A SUSCEPTIBLE GENOTYPE) AND ELITE SOYBEAN GENOTYPES BY MEASURING PHYSIOLOGICAL RESPONSES, (2) ELUCIDATE LIPID METABOLIC CHANGES IN TOLERANT AND SUSCEPTIBLE GENOTYPES UNDER HEAT STRESS, AND IDENTIFY CHANGES ASSOCIATED WITH TOLERANCE, AND (3) DETERMINE GENOMIC REGIONS (QTLS) AND MOLECULAR MARKERS ASSOCIATED WITH HEAT-INDUCED LIPID METABOLIC CHANGES AND OTHER HEAT TOLERANCE-RELATED TRAITS IN SOYBEAN. MOLECULAR MARKERS OF HEAT TOLERANCE WILL BE THE KEY DELIVERABLE FROM THIS PROJECT, WHICH WILL ADVANCE SOYBEAN BREEDING PROGRAMS IN DEVELOPING HEAT-TOLERANT VARIETIES. THE PROJECT WILL GENERATE FOUNDATIONAL KNOWLEDGE ON THE GENETIC BASIS OF LIPID BIOSYNTHETIC PATHWAYS AND OTHER PHYSIOLOGICAL MECHANISMS RELATED WITH HEAT TOLERANCE, WHICH WILL BE VALUABLE FOR CROP IMPROVEMENT PROGRAMS IN DEVELOPING CLIMATE-RESILIENT VARIETIES.