**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE LEAF BLADE IS A HIGHLY ORGANIZED PHOTOSYNTHETIC APPARATUS IN WHICH SOLAR ENERGY AND CARBON DIOXIDE FROM THE ATMOSPHERE ARE ASSIMILATED INTO SUGAR TO SUSTAIN LIFE ON EARTH. FOLLOWING ITS RECRUITMENT FROM PLURIPOTENT STEM CELLS OF THE SHOOT APICAL MERISTEM, THE LEAF PRIMORDIUM ORGANIZES ITSELF INTO DEFINED CELL LAYERS THROUGH HIGHLY REGIMENTED CELL DIVISION AND CELL EXPANSION PATTERNS FORMING A FLATTENED BLADE. BECAUSE THE LEAF BLADE FUNCTIONS AS A SOLAR PANEL, ITS SIZE AND DESIGN ARE OF FUNDAMENTAL INTEREST TO BASIC BIOLOGY, CROP PRODUCTIVITY, AND ENVIRONMENTAL ADAPTATION. HOWEVER, DESPITE EXTENSIVE RESEARCH AND TREMENDOUS PROGRESS, WE STILL KNOW RELATIVELY LITTLE ABOUT HOW BLADE EXPANSION IS CONTROLLED. STENOFOLIA (STF), A WOX FAMILY TRANSCRIPTION FACTOR IN MEDICAGO TRUNCATULA, IS CRITICALLY REQUIRED FOR BLADE OUTGROWTH AND PROMOTES CELL PROLIFERATION AT THE ADAXIAL-ABAXIAL JUXTAPOSITION THROUGH A TRANSCRIPTIONAL REPRESSION MECHANISM. WE RECENTLY UNCOVERED THAT ANOTHER WOX GENE, MTWOX9, REGULATES BLADE OUTGROWTH ANTAGONISTICALLY TO STF. MTWOX9 ACTS AS A TRANSCRIPTIONAL ACTIVATOR AND ENHANCES THE STF AND LAM1 MUTANT PHENOTYPES. THE MOLECULAR MECHANISM OF MTWOX9 FUNCTION IN LEAF BLADE DEVELOPMENT AND THE BASIS OF ITS ANTAGONISTIC ACTIVITY TO STF ARE UNKNOWN. THE OVERARCHING GOAL OF THIS PROPOSAL IS TO UNDERSTAND THE MOLECULAR MECHANISM OF MTWOX9 FUNCTION IN LEAF BLADE DEVELOPMENT AND UNCOVER THE MOLECULAR AND STRUCTURAL BASIS OF ITS ANTAGONISTIC RELATIONSHIP TO STF IN BLADE OUTGROWTH. THE PROJECT EXPLOITS THIS ANTAGONISTIC ACTIVITY OF STF AND MTWOX9 TO MANIPULATE ALFALFA TO IMPROVE FORAGE YIELD, NUTRITIONAL QUALITY, AND DIGESTIBILITY AND ADDRESSES THE AFRI PRIORITY AREA PHYSIOLOGY OF AGRICULTURAL PLANTS.