Pyrus calleryana Decne. is widely used as a pear rootstocks in Asia. Glutathione (GSH) can induce the phytochelatin synthase gene's (PcPCS1) transcription in this plant when exposed to cadmium. This phenomenon indicated that GSH plays a vital role in protecting P. calleryana from cadmium stress. Here, we have isolated and characterized a gene encoding.-glutamylcysteine synthetase (Pc gamma ECS), the key enzyme of GSH biosynthesis, from the leaves of P. calleryana, with the aim of expanding our knowledge of the role of GSH at the molecular level. P. calleryana plants treated with cadmium, salt, PEG6000, or mannitol responded by increasing transcription of the Pc gamma ECS gene. The response was specific for cadmium, which causes a toxicity that is thought to be mitigated through phtochelatins, and other treatments that cause damage that can be relieved by the synthesis of GSH. Feeding experiments suggested that cysteine contributed to activating the transcription of Pc gamma ECS and GSH synthesis. However, the gene's expression was inhibited in the presence of GSH. Recombinant Escherichia coli carrying Pc gamma ECS had higher GSH synthesis levels and grew better than the control cells under cadmium, salt, or osmotic stresses. These results suggest that Pc gamma ECS may participate in responses against multiple environmental stimuli in P. calleryana.
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