Identification and characterization of glutamine synthetase isozymes in Gracilaria lemaneiformis

•Six glutamine synthetase (GS) isoenzymes are identified and characterized.•GS is a key enzyme in N assimilation during the development and growth of plant.•The fundamental for the metabolic function of GS isoforms in macroalgae. Glutamine synthetase (GS) isozymes are necessary during the conversion of inorganic to organic nitrogen (N) and they also play a crucial role in the growth of Gracilaria lemaneiformis. Six genes encoding GS-protein were found and identified from the transcriptome data of G. lemaneiformis genome. No intron was found in the six GS genes. Among these six GS genes, Unigene0016999 and Unigene0017002 genes encode two GSI subfamily proteins with 426 and 507 amino acid (AA), respectively. These two GSI proteins are localized to the mitochondria and contain only one conserved Gln-syn C domain. Three GSII subfamily proteins (Unigene0015608, Unigene0022741 and Unigene0002184 with 350 AA, 350 AA and 402 AA respectively) harbor a conserved Gln-synt_C and Gln-synt_N domains. While Unigene0002194 gene encodes a GSIII protein (735 AA) and is comprised of a conserved Gln-synt_C and a specific GSIII_N domain. Phylogenetic analyses provided strong support for the classification of three GS subfamilies in G. lemaneiformis and insights into the evolutionary relationship of GS subfamilies between different organisms.