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138
Molecular Evolution of Glutamine Synthetase In Protists
Author(s) -
Robertson D. L.
Publication year - 2003
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.0022-3646.2003.03906001_138.x
Subject(s) - biology , protist , glutamine synthetase , plastid , photosynthesis , symbiosis , gene , phylogenetics , phylogenetic tree , botany , chloroplast , biochemistry , glutamine , genetics , bacteria , amino acid
Assimilation of nitrogen into structural and functional macromolecules is a critical process in all living organisms. Glutamine synthetase (GS) catalyzes the ATP‐dependent condensation of NH4+ and glutamate thus coupling nitrogen assimilation with carbon metabolism. The GS superfamily is comprised of three gene families: GSI, GSII, and GSIII. Representatives of the three gene families are found in prokaryotes, suggesting the genes are paralogous. In contrast, knowledge of the distribution and evolution of the GS gene families in eukaryotes is limited. The endosymbiotic origin of plastids is well established. Phylogenetic analyses of genes distributed among photosynthetic and non‐photosynthetic organisms may provide insight into the timing and stability of the endosymbiotic events. GSII has been characterized from a variety of prokaryotic and eukaryotic species, including the stramenopiles, Skeletonema costatum and Phytophthora infestans (AAN31463). I evaluated several a priori hypotheses regarding the placement of the stramenopile GSII sequences in addition to performing unconstrained analyses. In all analyses, GSII from S. costatum and P. infestans grouped together. Also, there was strong to moderate support for a ‘protist+plant’ clade, which included the vascular plants, photosynthetic algae, and the non‐photosynthetic P. infestans . Although it remains unresolved whether GSII was transferred from the nucleus of the endosymbiont early in the evolution of stramenopiles, the continued accumulation of GSII sequences from diverse eukaryotes should allow us to rigorously evaluate this hypothesis in the future.