Molecular cloning and characterization of a gamma-glutamylcysteine synthetase gene from Chorispora bungeana

Chorispora bungeana Fisch. and C.A. Mey (C. bungeana) is a rare alpine subnival plant species that is highly tolerant of freezing temperatures. Glutathione (GSH) is a major player in various metabolic processes involved in plant growth and development and stress responses. A recent study has found that the inhibition of GSH synthesis decreases the chilling tolerance of C. bungeana callus (J. Wu et al.: Cryobiology 57:9-17, 2008). We have isolated and characterized a full-length cDNA encoding gamma-glutamylcysteine synthetase (Cb gamma ECS), the key enzyme of GSH synthesis, from the leaves of C. bungeana, with the aim of furthering our understanding of the role of GSH at the molecular level. Cb gamma ECS was found to encode a 524-amino acid protein with moderate to high nucleotide sequence similar to previously reported plant gamma-ECS genes. Cb gamma ECS transcripts were detected in the calluses, roots and leaves of C. bungeana, but there was no tissue-specific expression. The transcripts of Cb gamma ECS accumulated both rapidly and at high levels when C. bungeana was treated with chilling (4 degrees C), freezing (-4 degrees C), several other environmental stresses (such as heat, salinity, osmotic and heavy metals), abscisic acid and hydrogen peroxide. These results suggest that Cb gamma ECS may participate in the cellular responses against multiple environmental stimuli in C. bungeana.