Characterisation of a cDNA encoding gamma-glutamylcysteine synthetase in Medicago truncatula

A gamma-ECS cDNA from Medicago truncatula was isolated using an Arabidopsis thaliana cDNA as probe. The analysis of the amino acid sequence deduced from this cDNA revealed 80% identity with the gamma-ECS from A. thaliana and Brassica juncea and suggested a plastidial localisation for the enzyme. Gamma-ECS activity and high level of GSH were detected in the gamma-ECS-deficient E. coli strain expressing a fusion protein containing the M. truncatula gamma-ECS protein. Southern blot analysis suggests that gamma-ECS is encoded by a small multigenic family in M. truncatula and shows that homologous genes are present in two other leguminous plants, Medicago sativa and Pisum sativum. Gamma-ECS gene expression was analysed by Northern blot in seedlings, plantlets and mature plants.