GLOBAL FOOD SECURITY AND THE DEMAND FOR HIGH-YIELDING, NUTRIENT-DENSE GRAIN CROPS ARE AMONG THE MOST URGENT AND AMBITIOUS DRIVERS OF MODERN PLANT SCIENCES DUE TO THE CURRENT TREND OF POPULATION GROWTH, EXTREME WEATHER CONDITIONS AND DECREASING ARABLE LAND RESOURCES. THESE OBSTACLES HAVE PUSHED THE UTILIZATION OF NUTRIENT-POOR MARGINAL LANDS FOR AGRICULTURAL PURPOSES. IT HAS BEEN KNOWN FOR DECADES THAT DEFICIENCY FOR A MICRONUTRIENT COPPER IN MARGINAL AS WELL AS ALKALINE, SANDY OR ORGANIC SOILS COMPROMISES PLANT FERTILITY AND REDUCES GRAIN/SEED YIELD WITH THE MOST NEGATIVE IMPACT ON WHEAT GRAIN PRODUCTION. GRAIN YIELD AND DRY MATTER ACCUMULATION (E.G., STARCH, PROTEINS, DIETARY FIBER) IN GRAINS DETERMINE THE CROP VALUE FOR THE HUMAN DIET, ANIMAL FEED AND GRAIN UTILIZATION IN THE FOOD INDUSTRY. THE TOTAL GRAIN YIELD AND DRY MATTER ACCUMULATION DEPEND ON THE PHOTOSYNTHETIC CAPACITY OF PLANT SOURCE TISSUES AND PHOTOASSIMILATES REMOBILIZATION TO SINK TISSUES. THIS PROPOSAL IS MOTIVATED BY OUR DISCOVERY IN A WHEAT MODEL BRACHYPODIUM, SHOWING THAT THE LOSS-OF-FUNCTION OF A COPPER TRANSPORTER YSL3 ALTERS COPPER DISTRIBUTION TO REPRODUCTIVE ORGANS AND GRAINS, REDUCES FERTILITY, AND SIGNIFICANTLY DECREASES GRAIN SIZE AND PROTEIN ACCUMULATION. OUR STUDIES IN WHEAT ALSO LINKED SOURCE-TO-SINK COPPER-REMOBILIZATION EFFICIENCY WITH PROTEIN ACCUMULATION IN GRAINS. HOW COPPER PARTITIONING IS RELATED TO STORAGE PROTEIN ACCUMULATION IN CEREAL GRAINS AND WHICH PROTEINS ARE IMPLICATED IN SOURCE-TO-SINK COPPER DELIVERY ARE UNKNOWN.THIS PROJECT USES WHEAT ALONGSIDE ITS MODEL BRACHYPODIUM AND COMBINES WHOLE-LEAF PHYSIOLOGY, FUNCTIONAL GENOMICS, HIGH-PRECISION PHENOTYPING STRATEGIES AND CO-EXPRESSION NETWORK ANALYSES TO: 1) ESTABLISH THE ROLE OF COPPER AND WHEATYSL3TRANSPORTER ON RESOURCE MOBILIZATION TO GRAINS; 2) COMPARE THE TRANSCRIPTIONAL RESPONSE OF BRACHYPODIUM AND WHEAT TO ALTERED SOURCE-TO-SINK COPPER DISTRIBUTION AND IDENTIFY NOVEL TRANSPORTERS ASSOCIATED WITH COPPER-USE EFFICIENCY AND PHOTOASSIMILATES DELIVERY TO GRAINS; 3) PHENOTYPE AND GENOTYPE THE WHEAT MAPPING POPULATION FOR COPPER RE-DISTRIBUTION EFFICIENCY, GRAIN SIZE, AND RESOURCE ALLOCATION. THE LONG-TERM GOALS OF THIS PROJECT ARE TO IDENTIFY CRITICAL COPPER-DEPENDENT TRAITS THAT DETERMINE RESOURCE ALLOCATION TO GRAINS, AND CONTRIBUTE APPROACHES FOR IMPROVING PRODUCTIVITY AND NUTRITIONAL QUALITY OF CEREALS GROWN ON MARGINAL SOILS.