**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** IN GRASSES, THE MOLECULAR CUES GOVERNING ROOT HAIR INITIATION AND SUBSEQUENT TIP GROWTH ARE NOT WELL UNDERSTOOD. THE LONG-TERM GOAL OF THIS PROJECT IS TO USE THE NITRATE-RESPONSIVE BUZZ MUTANT IN BRACHYPODIUM DISTACHYON, WHICH LACKS ROOT HAIRS AND HAS AN INCREASED ROOT GROWTH RATE WITH LITTLE EFFECT ON SHOOT TRAITS, AS A TOOL TO DETERMINE THE GENETIC AND PHYSIOLOGICAL UNDERPINNINGS OF TWO RELATED GROWTH PROCESSES: ROOT HAIR OUTGROWTH AND ROOT GROWTH RATE. THE OBJECTIVE OF THIS PROPOSAL IS TO ELUCIDATE THE SIGNALING MECHANISM USED BY BUZZ TO MEDIATE TIP GROWTH OF ELONGATING ROOT HAIRS AND INFLUENCE ROOT DEVELOPMENT, PARTICULARLY IN RESPONSE TO EXTERNAL NITRATE AVAILABILITY. THE CENTRAL HYPOTHESIS IS BUZZ REQUIRES INTERACTIONS WITH SPECIFIC PROTEINS TO PROPERLY FACILITATE ITS BIOCHEMICAL FUNCTION AND ACT ON A ROOT HAIR GROWTH PROMOTING PATHWAY. INCREASED KNOWLEDGE OF THIS REGULATOR WILL PROVIDE A FRAMEWORK FOR HOW ROOT HAIRS DEVELOP AND GROW IN ECONOMICALLY IMPORTANT GRASS CROPS ANDELUCIDATE HOW ROOT HAIRS AFFECT PHYSIOLOGICAL RESPONSES TO NUTRIENT AVAILABILITY, THEREBY GUIDING BREEDING EFFORTS TO IMPROVE NUTRIENT USE EFFICIENCY IN CROPS.