Modification of Limonoid Metabolism in Suspension Cell Culture of Citrus

Abstract

For the metabolic engineering of bio-functional substances in Citrus, metabolic changes of limonoids were investigated in embryogenic cell cultures of Citrus and Fortunella. When embryogenic cells of Citrus and Fortunella were cultured for four weeks in the liquid subculture medium containing nomilin, most species converted nomilin to obacunone and limonin. In addition, calamin group limonoids were produced in Fortunella and Calamondin cells. Deacetylnomilin was produced from nomilin in the cells of C. ichangensis and its related species. Exogenously added limonin into medium was not metabolized. The embryoid formation in C.aurantium did not affect the limonoid metabolism. All cells cultured without the presence of nomilin or limonin did not generate any limonoids. Furthermore, transgenic C. sinensis cell harboring a chimeric limonoid UDP-glucosyltransferase (limonoid GTase) gene was generated. The conversion of limonin into limonin 17-β-D-glucopyranoside (LG) demonstrated an efficient assay system for the transgene.