AbstractIn plants, nuclear Ca²⁺ releases are essential to the establishment of nitrogen-fixing and phosphate-delivering arbuscular mycorrhizal endosymbioses. In the legume Medicago truncatula, these nuclear Ca²⁺ signals are generated by a complex of nuclear membrane-localised ion channels including the DOES NOT MAKE INFECTIONS 1 (DMI1) and the cyclic nucleotide-gated channels (CNGC) 15s. DMI1 and CNCG15s are conserved among land plants, suggesting roles for nuclear Ca²⁺ signalling that extend beyond symbioses. Here we show that nuclear Ca²⁺ signalling initiates in the nucleus of Arabidopsis root cells and that these signals are correlated with primary root development, including meristem development and auxin homeostasis. In addition, we demonstrate that altering genetically AtDMI1 is sufficient to modulate the nuclear Ca²⁺ signatures, and primary root development. This finding supports the postulate that stimulus-specific information can be encoded in the frequency and duration of a Ca²⁺ signal and thereby regulate cellular function.