Molecular evolution of glutamine synthetase II: Phylogenetic evidence of a non-endosymbiotic gene transfer event early in plant evolution

Background Glutamine synthetase(GS) is essential for ammonium assimilation and the biosynthesis of glutamine. The three GS gene families(GSI, GSII, and GSIII) are represented in both prokaryoticand eukaryoticorganisms. In this study, we examined the evolutionary relationship of GSII from eubacterial and eukaryoticlineages and present robust phylogenetic evidence that GSII was transferred from γ- Proteobacteria(Eubacteria) to the Chloroplastida.