TO IMPROVE NITROGEN USE EFFICIENCY (NUE), IT IS CRUCIAL TO UNDERSTAND THE DYNAMIC GENE REGULATION THAT ALLOWS PLANTS TO RESPOND TO A CHANGING NITROGEN ENVIRONMENT. WE RECENTLY REPORTED DIFFERENTIAL EXPRESSION OF TRANSCRIPT ISOFORMS IN RESPONSE TO NITROGEN, THUS OPENING A NEW FRONTIER IN DECIPHERING MOLECULAR BASIS OF NITROGEN RESPONSE. HERE, I PROPOSE TO ELUCIDATE THE REGULATORY AND FUNCTIONAL MECHANISMS OF AMINO ACID VACUOLAR TRANSPORTER 1B (AVT1B) THAT UNDERGOES PROMINENT ISOFORM SWITCHING IN RESPONSE TO NITROGEN. WHEN NITROGEN IS PRESENT, AVT1B IS EXPRESSED AS THE FULL-LENGTH MRNA THAT ENCODES A PUTATIVE AMINO ACID TRANSPORTER; WHEN NITROGEN IS LIMITING, A TRUNCATED MRNA IS TRANSCRIBED WITH THE FIRST FOUR EXONS MISSING. TO TEST THE HYPOTHESIS THAT THE TRANSPORT ACTIVITY OF THE FULL LENGTH AVT1B IS MODULATED BY THE TRUNCATED AVT1B DURING NITROGEN STARVATION TO FINE-TUNE PLANT NITROGEN METABOLISM, I WILL PROBE THE REGULATORY MECHANISMS UNDERLYING THE ISOFORM SWITCH (OBJECTIVE 1), DETERMINE THE BIOCHEMICAL FUNCTION AND INTERACTION OF THE TWO ISOFORMS (OBJECTIVE 2), AND EVALUATE THE ROLE OF BOTH ISOFORMS IN PLANTA (OBJECTIVE 3). THE PROPOSED STUDY WILL UNCOVER MECHANISMS TYING ENVIRONMENTAL SIGNALS TO TRANSCRIPT PLASTICITY AND LIKELY IDENTIFY NEW TARGET GENES FOR BREEDING AND ENGINEERING TO INCREASE NUE. THIS PROPOSED PROJECT WILL PROVIDE VALUABLE TRAINING IN GENE REGULATION AND FUNCTIONAL GENOMICS, WHICH, COMBINED WITH MY BACKGROUND IN METABOLISM AND BIOCHEMISTRY, WILL ALLOW ME TO DEVELOP A STRONG RESEARCH PROGRAM. THE FELLOWSHIP WILL SUPPORT MY DEVELOPMENT TOWARD A WELL-ROUNDED SCIENTIST AND TEACHER WITH THE SKILLS NECESSARY TO BE SUCCESSFUL IN A TENURE-TRACK POSITION.