Optimal expression of GUS gene from methyl jasmonate-inducible promoter in high density culture of transformed tobacco cell line BY-2

The optimal expression of the β-glucuronidase (GUS) gene was studied in a tobacco cell line, BY-2, that was transformed with the GUS gene under the control of the cathepsin D inhibitor (CDI) promoter. In batch culture, the optimal induction time was in the late growth phase, and the optimal concentration of methyl jasmonate (MJ) was 0.7 mM. In fed-batch culture, the GUS specific activity when MJ was added several times was about 1.7-fold that when MJ was added only once. However, a significant decrease in the growth rate was observed after MJ addition. During the fed-batch culture, no medium components were depleted, and the presence of inhibitory metabolite(s) was observed. To remove inhibitory metabolite(s) from the medium, filtration culture was carried out, which gave a cell growth rate faster than that of the fed-batch culture. The final cell concentration and total GUS activity reached 480 g-fresh weight/l and 5.2 μkat/l, which were 1.3-fold and 1.5- fold the amounts obtained in fed-batch culture. The GUS specific activity using the CDI promoter was about 17-fold that obtained in a rbcS-promoter system studied previously. Efficient foreign gene production from transformed BY-2 cells was thus performed on a fermentor scale.