Flower color modification in Torenia fournieri by genetic engineering of betacyanin pigments

Abstract

Background Betalains are reddish and yellow pigments that accumulate in a few plant species of the order Caryophyllales. These pigments have antioxidant and medicinal properties and can be used as functional foods. They also enhance resistance to stress or disease in crops. Several plant species belonging to other orders have been genetically engineered to express betalain pigments. Betalains can also be used for flower color modification in ornamental plants, as they confer vivid colors, like red and yellow. To date, betalain engineering to modify the color of Torenia fournieri—or wishbone flower—a popular ornamental plant, has not been attempted. Results We report the production of purple-reddish-flowered torenia plants from the purple torenia cultivar “Crown Violet.” Three betalain-biosynthetic genes encoding CYP76AD1, dihydroxyphenylalanine (DOPA) 4,5-dioxygenase (DOD), and cyclo-DOPA 5-O-glucosyltransferase (5GT) were constitutively ectopically expressed under the cauliflower mosaic virus (CaMV) 35S promoter, and their expression was confirmed by quantitative real-time PCR (qRT-PCR) analysis. The color traits, measured by spectrophotometric colorimeter and spectral absorbance of fresh petal extracts, revealed a successful flower color modification from purple to reddish. Red pigmentation was also observed in whole plants. LC-DAD-MS and HPLC analyses confirmed that the additional accumulated pigments were betacyanins—mainly betanin (betanidin 5-O-glucoside) and, to a lesser extent, isobetanin (isobetanidin 5-O-glucoside). The five endogenous anthocyanins in torenia flower petals were also detected. Conclusions This study demonstrates the possibility of foreign betacyanin accumulation in addition to native pigments in torenia, a popular garden bedding plant. To our knowledge, this is the first report presenting engineered expression of betalain pigments in the family Linderniaceae. Genetic engineering of betalains would be valuable in increasing the flower color variation in future breeding programs for torenia.