The root system of plants is critically important for growth and survival and has been key to the success of the colonization of land by higher plants. The main functions of roots are that they anchor plants in the soil and that they allow to forage the soil for water and nutrients. The root system of many plants consists of a long primary root with regularly spaced lateral branches to optimize water and nutrient uptake. The regular pattern of lateral roots along the main root is controlled near the tip/meristem of the growing root and depends on a highly localized, peak of auxin, that triggers prebranch site production. We recently demonstrated that the periodic cell death in groups of cells that surround the meristem (lateral root cap) generates an auxin pulse that controls prebranch site production. However, in spite of extensive documentation of auxin transport mechanisms in the meristem, we were thus far unable to identify the molecular mechanism by which auxin is transported from the lateral root cap to the inner cell layers, where prebranch site formation occurs. This project will address this fundamental gap of knowledge by the systematic analysis of possible auxin transport mechanisms. This information will be an important step towards understanding how the regular pattern of lateral roots is established and how environmental signal are integrated in this pattern. Ultimately, this will help plant breeders to improve the water and nutrient uptake of crop species.