Effect of Overexpression of Secretory MT3 in Transgenic Plants on Enrichment of Cadmium in Plants
Metallothionein(MT),especially MT3,is the main protein involved in the detoxification of heavy metals within the human body.Previous studies have demonstrated that the alpha factor signal peptide(MF-α)from Saccharomyces cerevisiae mediates the secretion of recombinant protein EGFP outside plants.However,there is currently no available research on whether overexpression secretory MT3 in genetically modified plants affects their ability to accumulate cadmium(Cd),a heavy metal.In this study,we synthesized the fusion gene MF-α-EGFP-MT3 using artificial methods,which combines the signal peptide MF-α with enhanced green fluorescent protein(EGFP)and MT3.Subsequently,we constructed a plant expression vector pK-35S-MF-α-EGFP-MT3 carrying this fusion gene and transformed it into wild-type(WT)tobacco and Geranium plants to obtain transgenic plants.Using electrochemical methods,we detected the transcription level of MT3 in genetically modified plants and measured the level of EGFP-MT3 protein in the root exudates.After treating genetically modified plants with a Cd solution,we analyzed measured Cd content in roots,stems,and leaves through phenotype observation and electrochemical methods.Results showed that both genetically modified tobacco and Geranium transcribed the MT3 gene.Further-more,approximately 0.45～0.68 mg·g(based on fresh mass)of EGFP-MT3 protein was secreted by the root system.The transgenic tobacco plants treated with a 100 μmol·L-1 Cd exhibited a reduced damage phenotype and significantly higher chlorophyll content compared to the WT,indicating that the secretion of EGFP-MT3 can mitigate the toxic effects of cadmium.Genetically modified tobacco plants had approximately 40％higher accumu-lation of Cd in their roots,stems,and leaves compared to the WT.Transgenic Geranium plants were exposed to a 50 μmol·L-1 Cd.The results revealed a 30％increase in Cd accumulation in the roots and a four-fold higher accumulation in the stems of transgenic plants compared to those of WT.These findings provide evidence that the overexpression of EGFP-MT3 enhances the capacity of transgenic tobacco and Geranium plants to accumulate Cd,potentially due to an increased adsorption capacity resulting from the secretion of EGFP-MT3 on root surfaces and its accumulation within plant tissues.
transgenic plantsbeer yeast-α signal peptidemetallothionein secretionfusion geneCd enrichment
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