Generation of pink flower varieties from blue Torenia hybrida by redirecting the flavonoid biosynthetic pathway from delphinidin to pelargonidin

Transgenic torenia plants with various pink petal tones were obtained from blue or violet cultivars by combining downregulation of endogenous flavonoid 3′-hydroxylase (F3′H) and flavonoid 3′, 5′-hydroxylase (F3′5′H) genes with expression of a heterologous gene. Knockdown of the F3′H and F3′5′H genes in a blue torenia cultivar resulted in pale pink lines by decreasing the cyanidin and delphinidin levels and increasing the pelargonidin-based anthocyanin levels. Additional expression of rose dihydroflavonol 4-reductase (DFR) gene elevated the level of pelargonidin and yielded darker pink petals. Expression of pelargonidin DFR gene instead of the rose DFR gene increased the level of pelargonidin and darkened the petal color. Introducing the two genetic constructs containing a DFR gene into a violet torenia cultivar, which had more anthocyanins and a darker color than the blue one, further increased the level of pelargonidin and pink color intensity. These results reveal that selection of a suitable gene source and host greatly affects the phenotypes of the resultant transgenic plants.