The significance of the two cytosolic glutamine synthetase enzymes, GLN1;3 and GLN1;5, in the context of seed development and germination in Arabidopsis thaliana.

Glutamine synthetase (GS), an initial enzyme in nitrogen (N) plant metabolism, exists as a group of isoenzymes found in both cytosolic (GS1) and plastids (GS2) and has gathered significant attention for enhancing N use efficiency and crop yield. This work focuses on the A. thaliana GLN1;3 and GLN1;5 genes, the two predicted most expressed genes in seeds, among the five isogenes encoding GS1 in this species.

Arabidopsis thaliana mutants devoid of chloroplast glutamine synthetase (GS2) have non-lethal phenotype under photorespiratory conditions.

Chloroplast located Glutamine Synthetase (GS2) is believed to play a major role in the reassimilation of ammonium generated by photorespiration, being GS2 knockout mutants unable to grow under photorespiratory conditions (low-CO atmosphere) in the species characterized so far (Barley, Lotus). To investigate the importance of GS2 in A. thaliana nitrogen metabolism mutant plants devoid of this GS isoenzyme were characterized.