Responses to Systemic Nitrogen Signaling in Arabidopsis Roots Involve -Zeatin in Shoots.

Plants face temporal and spatial variation in nitrogen (N) availability. This includes heterogeneity in soil nitrate (NO) content. To overcome these constraints, plants modify their gene expression and physiological processes to optimize N acquisition. This plasticity relies on a complex long-distance root-shoot-root signaling network that remains poorly understood. We previously showed that cytokinin (CK) biosynthesis is required to trigger systemic N signaling. Here, we performed split-root experiments and used a combination of CK-related mutant analyses, hormone profiling, transcriptomic analysis, NO uptake assays, and root growth measurements to gain insight into systemic N signaling in By comparing wild-type plants and mutants affected in CK biosynthesis and ABCG14-dependent root-to-shoot translocation of CK, we revealed an important role for active -zeatin (Z) in systemic N signaling. Both rapid sentinel gene regulation and long-term functional acclimation to heterogeneous NO supply, including NO transport and root growth regulation, are likely mediated by the integration of content in shoots. Furthermore, shoot transcriptome profiling revealed that glutamate/glutamine metabolism is likely a target of Z root-to-shoot translocation, prompting an interesting hypothesis regarding shoot-to-root communication. Finally, this study highlights Z-independent pathways regulating gene expression in shoots as well as NO uptake activity in response to total N deprivation.