Glutamine Synthetase in Root Tips Promotes Root Elongation via Facilitating Nucleotide Metabolism Under Nitrogen Deficiency

Nitrogen deficiency is a major limiting factor for plant growth, yet the mechanisms underlying root growth under nitrogen-deficient conditions remain unclear. This study examined how glutamine synthetase (GS) in root tips mediates primary root elongation in wheat under nitrogen deficiency. We found that GS activity increased in root tips under nitrogen-limited conditions, promoting cell division in the meristematic zone by providing glutamine (Gln) for nucleotide biosynthesis. Metabolomic and transcriptomic analyses revealed that GS coordinated nitrogen assimilation with carbon skeletons flowing into glycolysis and the TCA cycle, ensuring a sufficient nucleotide supply for cell division. TaGS1;1, predominantly expressed in the meristematic zone, appears to be the key isoenzyme mediating these processes. This study shows that GS in root tips supports root elongation by driving nucleotide metabolism through Gln provision under nitrogen deficiency. These findings offer new insights into nitrogen signaling in root elongation and suggest potential strategies for improving nitrogen use efficiency in crops. • Nitrogen deficiency enhances GS activity in the wheat root tip. • GS promotes root elongation by boosting nucleotide synthesis and cell division. • GS reassimilates NH 4 + released from nucleotide turnover. • GS-dependent NH 4 + assimilation drives carbon flux into nucleotide synthesis. • TaGS1;1 is essential for root elongation under nitrogen deficiency.