Cloning And Expression Analysis Of Glutamine Synthetase Gene From Melon

Nitrogen availability is a common limiting factor for plant growth and development. Glutamine synthetase (GS) plays a central role in nitrogen metabolism in all plants. Plant GS occurs as a number of isoenzyme forms and these GS isoforms are located either in the cytosol (GS1) or plastid (GS2). We report the first cloning of a new plastid-located glutamine synthetase (GS) gene M-GS2 (GenBank accession number: AY773090) from melon (Cucumis melo. L). The cDNA of M-GS2 was isolated encoding a GS2 precursor polypeptide of 432 amino acids composing an N-terminal transit peptide of 53 amino acids and located in chloroplast. Sequence and structural analyses showed that M-GS2 protein contains GS beta-Grasp domain and GS catalytic domain that are conservative with other plant GS. The amino acid sequences derived from M-GS2 have extensive homology with GS2s from other higher plants. The phylogenetic tree displayed that the M-GS2 was most close to GS2 from Juglans nigra. Because of the GS importance on the nitrogen utilization,...