"The capacity of plants to withstand insect attack is of crucial importance for their fitness. Consequently, plants have developed intricate strategies to fend off herbivores and compensate for the negative impact of leaf-removal. Phytohormones, are responsible for many of these effects and are therefore widely recognized as key messengers in plant immunity. While the changes in leaves upon herbivore attack are well understood, it is becoming increasingly clear that the plant’s reaction involves the root system as well: Plants synthesize a variety of secondary metabolites and even defensive proteins in their roots that are then transported aboveground, they increase their assimilate uptake and storage capacity belowground to optimize regrowth after defoliation, and they reduce root expansion to liberate resources for leaf-defenses. Given the fact that roots actively respond to leaf attack, signals have to travel from the site of attack to the roots to induce the observed responses. Yet, until today, not a single herbivore induced leaf-to-root signal has been unambiguously identified.This project lays out a roadmap to discover the elusive leaf-to-root messengers using Nicotiana attenuata, one of the most advanced molecular and ecological plant-insect systems available today. The signaling cascade of N. attenuata has been thoroughly characterized in the leaves, and its root system is well known to be of central importance in plant defensive processes. By combining the N. attenuata system with novel analytical and molecular approaches, this project has the potential to considerably improve our understanding of the role of roots in aboveground processes and may lead to the identification of novel within-plant signals."