The survival of multicellular organisms requires inter-organ communication via long-distance signals. This is especially relevant in plants where post-embryonic development can be altered in response to sensing a heterogeneous nutrient environment in the soil. For example, a long-distance, inter-organ “root-shoot-root” relay system enables plant roots to specifically forage for nitrate-rich patches in a heterogeneous nutrient soil environment . In this proposal, I will use a unique “split-root” system to uncover the mechanisms of this systemic “root-shoot-root” relay system. Specifically, I will identify the targets of systemic N-signaling in plants as well as the potential RNA signals that traffic in phloem cells, the “information highway” to enable this inter-organ communication in plants. I will identify RNAs (mRNAs and smRNAs) associated with inter-organ signaling using a combination of time-based modeling and validate candidate genes using transgenics and shoot-root grafting. These studies will be the among the first to uncover systemic N-signals in a multicellular eukaryote.