Plants are sessile organisms whose growth and development rely on finely-tuned signaling mediated by plant hormones (phytohormones). One of the pivotal phytohormones commonly used in agriculture, gibberellic acid (GA), promotes a wide range of developmental processes in plants, such as seed germination, root and shoot elongation, flowering and fruit patterning. It is therefore crucial for plants to tightly regulate the biosynthesis and proper distribution of GA throughout their lifespan. However, little is known about how GA moves through cell membranes and where it is delivered during plant growth. We hypothesize that plants employ an undefined GA specific transporter to actively traffic GA in and out from the cell. Based on this idea, we have genetically screened for potential GA transporters in Arabidopsis using our newly developed fluorescent GA. Notably, we have discovered that NPF3.1 - a poorly characterized member of a large plant transporter family - efficiently transports GA across cell membranes both in vitro and in vivo. To the best of our knowledge, this is the first bona fide GA transporter identified. We propose that NPF3.1 plays a major role in regulating GA localization during plant growth and development, which we will examine through the following lines of investigation: 1) Investigate the biophysical properties of NPF GA transporters in vitro using the LC-MS-based and electrophysiological transport assays in Xenopus oocytes; 2) Solve the first atomic-resolution structure of NPF3.1 using X-ray crystallography; 3) Characterize the function and localization of NPF GA transporters during plant growth and development using a combination of genetics, fluorescence microscopy, and plant growth assays. Our proposed research is innovative because it is the first detailed investigation for an active GA transport mechanism. We expect to determine the spatiotemporal distribution of GA at the cellular level, as well as providing structural and mechanistic insights into the NPF transporters, which may be used to rationally intervene with GA delivery in plants. As genetic manipulation of GA biosynthesis and perception drove the first green revolution in world agriculture, we believe that controlling GA delivery through manipulation of GA transporters has the potential to generate a second green revolution to improve agricultural traits.