Electroporation-mediated transient gene expression in intact cells of sweetpotato

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Transient expression of the β-glucuronidase (GUS) gene has been studied in leaf-derived embryogenic callus of sweetpotato Ipomoea batatas L. (Lam.) by electroporation. The influence of several factors including electric field strength, buffer composition, time course of transient GUS gene expression, DNA concentration, enzyme, and polyethylene glycol (PEG) treatment was examined on GUS gene expression (number of blue spots). Maximum GUS gene expression (an average of 90 blue spots/fifty mg fresh weight callus tissue) was observed after 48 h when callus pieces were preincubated with electroporation (EPR) buffer for 1 h, followed by electroporation with a single electric pulse of 500 V/cm discharged from a 960-μF capacitor in the presence of 20 μg DNA/ml and 8.3 μl NaCl (3 M). Changing the electroporation buffer conductivity (by varying the buffer composition with low-high salt concentrations), had only slight effect on the number of blue spots. Similarly, the time course study of GUS gene expression revealed that GUS activity could be detected 12 h after electroporation with a maximum activity after 72 h (112 blue spots). Increasing the amount of DNA from 5 to 50 μg/ml in the EPR buffer had a slight effect on the expression frequency (from 20-110 blue spots, and 112 blue spots with 20 μg/ml). The number of blue spots was increased by enzymatic wounding of callus pieces for 10 min and by addition of 200 μl PEG 4000 (15%) before electroporation. These results suggest that intact cell electroporation can be used for producing transgenic sweetpotato tissue.

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