Factors affecting transient expression of vector constructs in wheat protoplasts

Direct uptake of reporter gene constructs with the bacterial beta-glucuronidase (GUS) gene fused to various promoters was achieved to embryogenic cell suspension culture-derived protoplasts of GK Ságvári winter wheat (Triticum aestivum L.) with polyethylene glycol (PEG) treatment. Based on GUS specific activity values, it was found that Mg2+ with PEG at 20% final concentration can significantly increase the transient expression in wheat protoplasts in comparison to the Ca(2+)-containing medium. The optimum incubation time in transformation mixture was 5-10 min at 25 degrees C. Transient GUS expression as detected by spectrofluorimetry was positively correlated with the time elapsed after DNA uptake (with maximum activity at 48 h), and the incubation time in GUS reaction mixture. It was also found that the protoplast culture medium plays an important role in the efficiency, and the treated wheat protoplasts cultured in KM medium showed a higher GUS activity than those kept in GM medium. Among the five plasmid constructs 6-16-fold higher promoter activity has been achieved with pKM794 driven by CaMV 35S promoter plus two enhancer elements than with the other constructs tested.