Production of recombinant miraculin protein in carrot callus via Agrobacterium-mediated transformation

Abstract

Miraculin is a taste-modifying protein that interacts with human sweet-taste receptors and transforms a sour taste into sweet taste. Miraculin is extracted from the miracle fruit (Synsepalum dulcificum). Since mass production of miraculin is difficult because of regional and seasonal limitations, several attempts have been made to express miraculin in various cell systems. In this study, a binary vector containing the miraculin gene under the control of the SWPA2 promotor was introduced into carrot (Daucus carota) callus via Agrobacterium-mediated transformation to synthesize miraculin in carrot cell cultures. After 4 weeks of co-cultivation with Agrobacterium tumefaciens, 20 tentative transgenic callus (TC) lines were obtained on kanamycin selection medium. PCR analysis confirmed that 18 of these 20 lines (TC1-TC18) carried the miraculin gene, and 4 TC lines with high cell growth and gene expression (determined by RT-qPCR) were selected for further analysis. Protein analysis of these four TC lines by SDS-PAGE and Western blot showed that the miraculin protein was stably produced in TC lines. The cell growth showed no correlation with gene expression levels. The DNA content and G1 phase ratio were negatively correlated, whereas the S and G2/M phase ratios were positively correlated with gene expression. The ratio of cell cycle was determined by counting the number of cells in each step through flow cytometric analysis. These results indicate that gene expression was higher in TC lines with active cell division. Overall, our results demonstrate the feasibility of mass production of recombinant miraculin protein in transgenic cell culture systems.