Cadmium and Arsenic responses in the ectomycorrhizal fungus Laccaria bicolor: glutathione metabolism and its role in metal(loid) homeostasis
Ectomycorrhizal fungi play an important role in protecting their host plant from metal(loid) stresses by synthesizing various thiol rich compounds like metallothioneins and glutathione. We investigated the effect of cadmium (Cd) and arsenic (As) stress with a specific interest on glutathione (GSH) in the ectomycorrhizal fungus Laccaria bicolor. The total GSH levels inside the cell were significantly increased with increase in external metal(loid) stress. An analysis of the transcript levels of genes responsible for GSH synthesis, γ‐glutamylcysteinesynthetase (Lbγ‐GCS) and glutathione synthetase (LbGS), using qPCR revealed that expression of both genes increased as a function of external metal(loid) concentration. The enzyme activity of both Lbγ‐GCS and LbGS were increased with increase in external Cd and As concentration. Further, the functional role of Lbγ‐GCS and LbGS genes in response to Cd and As stress was studied using their respective yeast mutant strains gsh1Δ and gsh2Δ. The mutant strains successfully expressed the two genes resulting in wild‐type phenotype restoration of Cd and As tolerance. From these results, it was concluded that GSH act as a core component in the mycorrhizal defense system under Cd and As stress for metal(loid) homeostasis and detoxification.
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