FLOODING EVENTS INCREASINGLY OCCUR IN AGRICULTURAL SYSTEMS AND SIGNIFICANTLY IMPACT CROP YIELD. INUNDATION OF DRY-LAND CROPS SUCH AS SOYBEAN (GLYCINE MAX) IS TYPICALLY LIMITED TO WATERLOGGING OF THE ROOT SYSTEM, IN CONTRAST TO SUBMERGENCE OF THE ABOVE-GROUND ORGANS KNOWN TO IMPACT PRODUCTION OF RICE. WATERLOGGING TOLERANCE IS ASSOCIATED WITH ROOT ADAPTATIONS THAT INCREASE GROWTH AND SURVIVAL OF ROOTS UNDER HYPOXIC CONDITION. WE HAVE MAP-BASED CLONED AND VALIDATED A CANDIDATE GENE UNDERLYING A MAJOR WATERLOGGING-TOLERANCE QTL (QWT_GM03), WHICH FIRSTLY DESCRIBED NATURAL-VARIATION ASSOCIATED WITH WATERLOGGING-TOLERANCE IN A DRYLAND CROP. THE CANDIDATE GENE ENCODES A SMALL-AUXIN-UP-REGULATED (SAUR) PROTEIN THAT INFLUENCES ROOT DEVELOPMENT UNDER WATERLOGGING. THE MAJOR NUCLEOTIDE VARIATION DISTINGUISHING THE ALLELES OF SAUR-FT (FLOODING TOLERANT) IS A 17-BP DELETION WITHIN THE 5' UNTRANSLATED-REGION (UTR), WHICH WE HYPOTHESIZE MODULATES CONDITION-SPECIFIC MRNA STABILITY OR TRANSLATION. THIS PROJECT WILL CHARACTERIZE THE TOLERANCE MECHANISM CONFERRED BY SAUR-FT, INCLUDING THE ALTERATIONS IN ROOT DEVELOPMENT, AND IMPACT ON SOYBEAN PRODUCTION. OBJECTIVE 1 WILL FURTHER CHARACTERIZE THIS NATURAL-GENETIC VARIANT. OBJECTIVE 2 WILL VALIDATE THE ROLE OF THE PROMOTER AND A PURINE (R)-RICH MOTIF IN THE 5'UTR OF SAUR-FT IN GENE REGULATION AND THE OUTCOME OF THIS REGULATION ON ROOT DEVELOPMENT. OBJECTIVE 3 WILL EVALUATE THE AGRONOMIC IMPORTANCE OF QWT_GM03/SAUR-FT AND DEVELOP WATERLOGGING-TOLERANT AND HIGH-YIELDING GERMPLASM. THE OUTCOME WILL BE KNOWLEDGE OF FUNCTIONAL GENE(S) AND DEVELOPMENT MECHANISMS THAT STABILIZE YIELDS OF SOYBEAN THREATENED BY FLOODING EVENTS FOR THE FIRST TIME. THE WATERLOGGING-TOLERANT SOYBEAN GERMPLASM LINES WILL ALSO BE DEVELOPED AND MADE AVAILABE FOR BOTH PUBLIC AND PRIVATE BREEDING SECTORS. THESE DISCOVERIES WILL DIRECT FUTURE STRATEGIES FOR INCREASING WATERLOGGING-RESILIENCE OF OTHER DRYLAND CROPS, SUCH AS MEDICAGO, WHEAT AND MAIZE.