The regulation of C/N signaling is essential to ensure proper plant growth according to the environmental conditions. Because of the rise in atmospheric CO 2 concentration, C/N balance in plants is currently disrupted, and this leads to major modifications in plant growth and physiology (Gojon et al., 2023). We recently followed a Genome-Wide Association approach that identified several genes associated with the alteration of N status under elevated CO 2 (Cassan et al., 2023). Among these genes, we report here the characterization of the transcription factor GATA4. We notably show that the natural variation of N content under high CO 2 is due to the haplotype-dependent expression of GATA4. Moreover, the analysis of gata4 knock-out mutant, along with transcriptomic analyses, reveal that GATA4 is a potential integrator of C/N signaling. Indeed, the gata4 mutant has reduced growth, biomass and N content compared to wild-type plants under elevated CO2, and several major actors of C and N metabolism were identified as direct targets of GATA4, including GLN2, NLPs and cell wall remodeling genes. This work positions GATA4 as a major regulator of C/N signaling, and unveils novel molecular mechanisms influencing C and N metabolisms under elevated CO2 in Arabidopsis. Cassan, O., Pimparé, L.-L., Mozzanino, T., Fizames, C., Devidal, S., Roux, F., Milcu, A., Lèbre, S., Gojon, A., and Martin, A. (2023). Natural genetic variation underlying the negative effect of elevated CO2 on ionome composition in Arabidopsis thaliana. eLife 10.7554/elife.90170.1. Gojon, A., Cassan, O., Bach, L., Lejay, L., and Martin, A. (2023). The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal. Trends in Plant Science 28:185-198. 10.1016/j.tplants.2022.09.002.