Glutathione S-Transferase (GST) Identified from Giant Kelp Macrocystis pyrifera Increases the Copper Tolerance of Synechococcus elongatus PCC 7942

The glutathione S-transferases gene family plays an important regulatory role in growth and development, and responses to environmental change. In this study, six complete GST genes ( MpGST 1 , MpGST 2, MpGST 3, MpGST 4, MpGST 5, and MpGST 6) were cloned from the gametophytes of brown alga Macrocystis pyrifera . Subsequent bioinformatics analysis showed that these six genes encoded proteins with 202, 216, 288, 201, 205, and 201 aa, respectively. Moreover, MpGST3 differs from the other GST genes. Phylogenetic analysis suggested that MpGST3 belongs to the Ure2p type GST. Domain analysis suggested that the other GSTs from M. pyrifera belong to the soluble GST family and form an independent branch with the GSTs found in the other macroalgae, suggesting that a new GST type was formed during macroalgal evolution. GST genes were upregulated in M. pyrifera when 2.5 mg L −1 Cu ions were added to the medium. Six GST genes were integrated into the genome of Synechococcus elongatus PCC 7942, and their functions were verified by measuring light absorbance, photosynthetic pigment content, and photosynthetic parameters of the transformed strains under 0.3 mg L −1 Cu ion stress. The results showed much higher levels of various parameters in the transformed strains than in the wild strain. The transformed strains (with the MpGST genes) showed significantly enhanced resistance to Cu ion stress, while the wild strain almost died. The results of this study lay a theoretical foundation for further research on the Cu ion stress resistance function of GSTs in M. pyrifera .