Nitrate acts at the Arabidopsis thaliana shoot apical meristem to regulate flowering time

Summary Optimal timing of flowering, a major determinant for crop productivity, is controlled by environmental and endogenous cues. Nutrients are known to modify flowering time; however, our understanding of how nutrients interact with the known pathways, especially at the shoot apical meristem ( SAM ), is still incomplete. Given the negative side‐effects of nitrogen fertilization, it is essential to understand its mode of action for sustainable crop production. We investigated how a moderate restriction by nitrate is integrated into the flowering network at the SAM , to which plants can adapt without stress symptoms. This condition delays flowering by decreasing expression of SUPRESSOR OF OVEREXPRESSION OF CONSTANS 1 ( SOC 1 ) at the SAM . Measurements of nitrate and the responses of nitrate‐responsive genes suggest that nitrate functions as a signal at the SAM . The transcription factors NIN ‐ LIKE PROTEIN 7 ( NLP 7) and NLP 6, which act as master regulators of nitrate signaling by binding to nitrate‐responsive elements ( NRE s), are expressed at the SAM and flowering is delayed in single and double mutants. Two upstream regulators of SOC 1 ( SQUAMOSA PROMOTER BINDING PROTEIN ‐ LIKE 3 ( SPL 3 ) and SPL 5 ) contain functional NRE s in their promoters. Our results point at a tissue‐specific, nitrate‐mediated flowering time control in Arabidopsis thaliana .