Plants are sessile organisms whose growth and development rely on finely-tuned signaling mediated by plant
hormones (phytohormones). One of the pivotal phytohormones, gibberellic acid (GA), promotes a wide range of developmental processes in plants, such as seed germination, root and shoot elongation, fiber and cambium development, flowering time and fruit patterning. It is therefore crucial for plants to tightly regulate the distribution of GA throughout their lifespan. Our original HFSP team, in parallel to colleagues in the field, demonstrated that a class of nitrate/peptide transporters (NPFs) actively transport GA and play major roles in GA delivery and response. However, we still do not know the mechanism by which the GA transporters select and move their substrates. One of the major impediments is the lack of high-resolution structures. Also, functional redundancy severely hampers genetic studies to investigate the contribution of each transporter in plant growth.

To understand the mechanisms of active GA transport in plants, our team will address the following three objectives: 1) Uncover the molecular mechanisms of key novel NPF GA transporters using a combination of structural and functional studies; 2) Investigate the physiological functions of active GA transport in root development and fiber formation using genetic, cellular, and systems biology approaches; and 3) Identify novel GA transporters, beyond the NPF family.

These objectives will require innovative techniques, for instance, we will overcome functional redundancy using our unique multi-targeted forward-genetic cell-type-specific transportome-scale screening. Our comprehensive studies on GA delivery at multiple levels—from the molecular and cellular mechanisms of individual transporters to the GAtrafficking protein network in the plant body—will greatly facilitate the design of GA-transporter specific modulators and deliver crucial knowledge on the mechanisms of active GA transport in plants. As genetic manipulation of GA biosynthesis and perception drove the first Green Revolution in world agriculture, controlling GA delivery through manipulation of GA transporters has the potential to generate a second Green revolution to improve agricultural
traits.