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A Medicago truncatula homoglutathione synthetase is derived from glutathione synthetase by gene duplication

Frendo, P., Jimenez, M.J.H., Mathieu, C., Duret, L., Gallesi, D., Van de Sype, G., Herouart, D., Puppo, A.
Plant physiology 2001 v.126 no.4 pp. 1706-1715
glutathione, leucine, complementary DNA, molecular weight, proline, alanine, phylogeny, amino acid sequences, gene expression, genes, nucleotide sequences, genetic complementation, glutathione synthase, glycine (amino acid), Medicago truncatula
Glutathione (GSH) and homo-GSH (hGSH) are the major low-molecular weight thiols synthesized in Medicago truncatula. Two M. truncatula cDNAs (gshs1 and gshs2) corresponding to a putative GSH synthetase (GSHS) and a putative hGSH synthetase (hGSHS) were characterized. Heterologous expression of gshs1 and gshs2 cDNAs in an Escherichia coli strain deficient in GSHS activity showed that GSHS1 and GSHS2 are a GSHS and an hGSHS, respectively. Leucine-534 and proline-535 present in hGSHS were substituted by alanines that are conserved in plant GSHS. These substitutions resulted in a strongly stimulated GSH accumulation in the transformed E. coli strain showing that these residues play a crucial role in the differential recognition of beta-alanine and glycine by hGSHS. Phylogenetic analysis of GSHS2 and GSHS1 with other eukaryotic GSHS sequences indicated that gshs2 and gshs1 are the result of a gene duplication that occurred after the divergence between Fabales, Solanales, and Brassicales. Analysis of the structure of gshs1 and gshs2 genes shows they are both present in a cluster and in the same orientation in the M. truncatula genome, suggesting that the duplication of gshs1 and gshs2 occurred via a tandem duplication.