Chloroplast-Expressed Glutamine Synthetase in Glycine and Related Leguminosae: Phylogeny, Gene Duplication, and Ancient Polyploidy

Abstract

Abstract The nuclear gene encoding the chloroplast-expressed isozyme of glutamine synthetase (ncpGS) is single copy in diploid angiosperms but is duplicated in species of Glycine, a paleopolyploid genus. The two Glycine paralogues are sister to one another in phylogenetic analyses, a pattern that suggests that this ncpGS duplication occurred subsequent to the divergence of Glycine from extant Glycininae. This pattern does not support an allopolyploid hypothesis in which genomes from close relatives of extant genera combined to form the polyploid, 2n = 40 genome of Glycine, nor with an ancient gene duplication shared with other Glycininae. Rather, it is consistent with autopolyploidy or with a simple gene duplication. Teramnus ncpGS was the closest relative of the two Glycine paralogues, supporting a sister-group relationship between these two genera. In contrast, ncpGS results suggested that Sinodolichos, a genus that has been suggested as a possible congener of Glycine, is more closely related to Pseuemi...